Research ArticleInfluential Factors of the Static Shear Properties of Coral Mud inthe South China Sea

Yang Shen 12 Xiaoxi Rui 12 Long Yang 12 Shaoyu Li 12 and Xue Shen 12

1Key Laboratory of Geomechanics and Embankment Engineering of Ministry of Education Hohai UniversityNanjing 210024 China2Jiangsu Research Center for Geotechnical Engineering Technology Hohai University Nanjing 210024 China

Correspondence should be addressed to Xiaoxi Rui 18251877144163com

Received 10 May 2020 Revised 2 August 2020 Accepted 11 August 2020 Published 24 August 2020

Academic Editor Castorina S Vieira

Copyright copy 2020 Yang Shen et al is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Coral mud a kind of special material used for constructing islets in reclamation projects is widely spread in the South China SeaCombined with microstructure research a series of triaxial tests were performed in this paper to study the static shear strengthcharacteristics and potential factors that can influence theme effective stress path was similar to the total stress path because ofthe unique microstructure resulting in a high strength and a high dissipation rate of the pore pressure in the coral mude initialvoid ratio and the initial confining pressure affected the strength and deformation characteristics of the coral mud When the soilcame to failure the pore pressure coefficient Af varied linearly with the initial void ratio e critical friction angle was greatlyinfluenced by the confining pressure and its magnitude first developed to a peak value and then decreased as the void ratioincreased is change showed that there was a linear relationship between the initial elastic modulus E0i and lgp0 as well asbetween the secant modulus E50 and p0 e estimation ability of Cam-Clay was verified in this researche value of parameter λwas determined incrementally by a larger initial void ratio while the value of parameterM decreased smoothly first and then roseslightly the selection of parameter κwas approximately 00035e results supported that the Cam-Clay model is able to simulatethe stress-strain relationship of coral mud and a referenced estimation can be reliably and efficiently obtained for the reclamationprojects of constructing islets

1 Introduction

e South China Sea covers a vast area and enjoys a superiorgeographical location and strategic position [1] In recentyears China has accelerated the development and utilizationof coral reefs in the South China Sea During the fillingprocess calcareous soil with large particles is first depositedat the bottom under gravity while small particles referred toas coral mud are suspended in the water to form silty sandafter drifting [2] According to the national panel surveycoral mud is one of the most important submarine sedi-ments in the eastern part of the South China Sea accountingfor 612 of the total sediments [3] In addition because ofthe intermittent construction of the filling operation thecoral soil layer presents a discontinuous distribution in thefoundation As a weak interlayer whose settlement and

bearing capacity will inevitably affect the whole foundationit is necessary to conduct in-depth and systematic researchon the shear characteristics of coral mud to provide scientificand reasonable design parameters for the engineeringconstruction of coral reefs

e mineral composition of coral mud is similar to thatof calcareous sand with up to 96 calcium carbonate Alarge number of research studies have been devoted to in-vestigating the factors influencing the shear properties ofcalcareous sand including the confining pressure densityparticle breakage [4] and shear rate [5] Studies have foundthat the shear characteristics of calcareous sand are greatlydependent on the confining pressure [6] If the confiningpressure increases then the strain under peak stress in-creases [7] and the initial response under a low confiningpressure is rigid with an obvious yield point and strain

HindawiAdvances in Civil EngineeringVolume 2020 Article ID 8856987 17 pageshttpsdoiorg10115520208856987

hardening stage [8] e impact of dilatancy on shearstrength is far greater than that caused by particle breakage[9 10]

According to particle size classification coral mud is siltyor silty clay Geotechnical tests have shown that the watercontent is an important factor influencing the shear prop-erties of clay and silt Zhang et al [11 12] proposed theinfluence of the water content on red clay specifically withan increase in the water content the peak cohesion andresidual cohesion decrease and the strain changes fromsoftening to hardening Xu et al [13 14] found that the porepressure and cohesion increase when Shanghai soft soil isdamaged Feng et al conducted a series of tests on silty clayand found that the failure shear strain value of silty soildecreases with increasing water content [15] and strainsoftening shows a weakening trend [16] Wang et al [17]found that the relationship between the cohesion and watercontent of calcareous silt can be represented by anM-shapedcurve e water contents corresponding to the two peaks ofthe M-type curve increase with increasing dry density

At present research on coral mud is scarce and hasmostly been focused on the permeability sedimentary as-pects Shen et al [18] considered the initial concentration tohave a significant impact on the isovelocity deposition timeof the coral mud Wang [2] found that the coefficient ofpermeability of coral mud decreases with increasing densitywhen the initial moisture content remains the same andreaches a maximum at saturation Based on the existingresearch of calcareous sand and silty clay the effects of theconfining pressure and water content on coral mud werestudied Considering that in the saturated triaxial test thewater content can be controlled by the initial void ratio [19]and the initial void ratio is a parameter of the Cam-Claymodel in this paper the initial confining pressure and theinitial void ratio were taken as variables Taizhou soil wasused as the control group e applicability of the Cam-Claymodel was discussed by comparing the simulation resultswith the experimental results

2 Materials and Methods

Based on laboratory experiments the static shear charac-teristics of coral mud samples were measured and comparedwith those of Taizhou soil in Zhejiang Province e testingresults are presented and discussed with respect to thefollowing (1) stress-strain relationship (2) pore pressuredevelopment (3) stress path (4) friction angle (eg mo-bilized friction angle critical state friction angle and peakstate friction angle) (5) modulus (eg initial elastic modulusand secant modulus) and (6) estimation ability of the Cam-Clay model

21 Physical Characteristics of Materials e coral mud fortesting was obtained from the seabed of a reef in the SouthChina Sea Coral mud is a loose unconsolidated powderydeposit light yellow to white in colour To highlight theunique physical andmechanical characteristics of coral mudTaizhou soil with similar liquid limits plastic limits and

particle gradations was selected for comparison in consol-idated undrained triaxial tests e images of coral mud andTaizhou soil are provided in Figure 1

An X-ray diffractometer was used to analyse the mineralcomposition and tabulate the results in Table 1 Figure 2presents the distributions of each soil particle sizeAccording to the standard [20] coral mud is silty clay with auniformity coefficient of Cu 375 and coefficient of cur-vature Cc 04 it is classified as poorly graded soil Table 2provides the basic characteristics

22 Microstructure of the Materials e microstructures ofcoral mud and Taizhou soil were magnified by 50 k withscanning electron microscopy (SEM) As shown inFigure 3(a) the granule morphology consisted of mainlystrips and needles with a small amount of irregular particlesand obvious pore development Figure 3(b) shows that mostparticles of Taizhou soil were clustered together in the formof aggregates where small particles were attached on thesurface of the large particles mainly in face-to-face contact

Forty representative particles were randomly selected toobtain the shape parameter circular degree R and ring di-ameter ratio T [21ndash23] R measures the edges and cornersWhen R 1 the particle is round T represents the ratio ofthe longest axis to the shortest axis of the particle e largerthe value is the closer the particle is to the dendritic shape[24] As shown in Figure 4 R(coral mud) is mainly distributedbetween 058 and 074 while T is between 312 and 487consistent with the statistical average values of R and T(0687 and 4178) Compared with the mean values of R(0915) and T (1512) in Taizhou soil the particle mor-phology of coral mud is extremely irregular due to its specialsedimentary environment and chemical composition

23 Testing Program In this study we first used X-raydiffraction and SEM to understand the chemical composi-tion and microscopic fabric of the testing materials Afterthat the effects of the initial confining pressure and initialvoid ratio on the shear properties were investigated by CUshear tests

e apparatus used in the triaxial tests was an LSY30-1stress-strain controlled triaxial instrument e sampleswere evenly mixed and stored in a humidor for 24 h beforebeing divided into five layers with the same mass and heightAfter 24 h of vacuum saturation the samples were loadedinto a pressure chamber and then the reverse pressuresaturation method was adopted until ΔuΔσ3gt098 especimen has a diameter of 391mm a height of 80mm andan axial shear rate of 004mmmin e testing program isprovided in Table 3

3 Results and Discussion

31 Stress-Strain Relationship

311 Effects of the Initial Confining Pressure e initial voidratio was 083 and CU shear tests were performed on thecoral mud and Taizhou soil under four confining pressures

2 Advances in Civil Engineering

of 100 kPa 200 kPa 300 kPa and 400 kPa (backpressure50 kPa) e stress-strain behaviours are given in Figure 5e strengths of the two soil samples both significantlyincrease with increasing confining pressure especially thestrength of the coral mud of adjacent confining pressurewhich increases by nearly 500 kPae strength of coral mudwas much higher than that of Taizhou soil under the same

confining pressure For a quantitative comparison we cal-culated the c and φ of the two soil samples and calculated themean values (Table 4) e mean internal friction angle ofTaizhou soil is 15deg in line with the values of engineeringexperience which is generally 15deg to 25deg but far smaller thanthose of coral mudis result could be attributed to the slip-like structure and unique physicochemical properties of

Perc

enta

ge fi

ner

Coral mudTaizhou soil

100 10 1 011000Particle size (μm)

0

20

40

60

80

100

Figure 2 Particle size distribution

Table 2 Basic characteristics of coral mud and Taizhou soil

Type Specific gravity Gs Liquid limit wL Plastic limit wp Plastic index Ip

Coral mud 277 338 23 108Taizhou soil 271 334 224 110

(a) (b)

Figure 1 Images of (a) coral mud and (b) Taizhou soil

Table 1 Mineral composition of coral mud and Taizhou soil

TypeMineral composition Chemical component

Percentage mass of various minerals (Wt ) Percentage of mass of each element (Wt )

Coral mud Biogenic calcium carbonate (Mg129Ca871) CO3 Ca Mg O C606 394 387 1 483 121

Taizhou soil SiO2 (Mg003Ca097) CO3 Ca Si O C927 73 29 433 529 09

Advances in Civil Engineering 3

coral mud making the bite force generated by interparticleembedding large and strong

In addition the stress-strain growth trends of the two arealso significantly different e stress of coral mud increasesrapidly at the initial stage of shear when ε is 1 the stressreaches approximately 23 of the shear strength and theelastic modulus in the early stage is positively correlated withthe confining pressure In contrast only when the confiningpressure is 100 kPa does the Taizhou soil curve show aplatform e stress under other confining pressures sta-bilizes or even slightly decreases at approximately 50 kPabefore ε 2 and increases sharply between 2 and 3After ε 3 the stress shows an increase with a steady ratewhose amplitude accounts for 14 to 12 of the total stress

From a microperspective this increase could be a resultof various particle contact responses Previous studies[25 26] have shown that the contact between particles in-cludes frictional contact and cemented contact e contactof Taizhou soil is cemented contact and its stress-strainbehaviour can be divided into the following three stages (1)the OA stage where the stress increases linearly (2) the ABstage where cement begins to break or extrude in which thestress develops smoothly or even declines at this stage and(3) the BC stage where particles come into direct contacte stress increases rapidly at this stage and its growth rate

is greater than that at the OA stage Due to the lack ofcementing materials coral mud skips the OA and AB stagesIts irregular particles come into direct contact from thebeginning and the stress levels off after a rapid increase

312 Effects of the Initial Void Ratio Figure 6 shows thestress-strain relationship with different initial void ratios ofcoral mud and Taizhou soil For Taizhou soil the stress-strain behaviours of different e0 values are roughly the sameas the deviatoric stress rising by a small margin with adecrease in e0 In addition the strain when the stress surgesdeclines with decreasing e0 which means that the cement ismore likely to be extruded and the particles are more likelyto come into direct contact with each other under high drydensity conditions In contrast the coral mud is moresignificantly affected manifested as the diverse variationtrend as well as the D-value which can reach 500 kPa Whene0 089 the stress-strain plot is obviously different in that itis an enhanced curve whose peak stress is higher thane0 083 under different confining pressures From theperspective of elastoplasticity when the pressure increasesthe coral mud with a large porosity transits from the elasticstage to the ideal plastic stage where part of the structure isbroken Its particles are more prone to particle dislocation

(a) (b)

Figure 3 SEM image of the testing materials (a) coral mud and (b) Taizhou soil

0 20 40 60 8004

06

08

10

R

Coral mudTaizhou soil

(a)

Coral mudTaizhou soil

0 20 40 60 800

1

2

3

4

5

T

(b)

Figure 4 Shape parameters of the testing materials (a) circular degree and (b) ring diameter ratio

4 Advances in Civil Engineering

and rearrangement which fills the pores and brings about agrowth in the shear strength when e0 089 [27] Taizhou soilhas no such feature owing to its shape and cementingsubstance which do not facilitate maloperation and oc-clusion friction compared with needle-like particles [28]

32 Pore Pressure Development

321 Effects of the Initial Confining Pressure In this part wecontrolled e0 069 to study the development law of the porepressure under different confining pressures As shown in

Table 3 Program of CU shear tests

Number p0 (kPa) ρd (gcm3) e0 w0 ()

CMA01 100 147 089 32CMA02 200 147 089 32CMA03 300 147 089 32CMA04 400 147 089 32CMA05 600 147 089 32CMB01 100 151 083 30CMB02 200 151 083 30CMB03 300 151 083 30CMB04 400 151 083 30CMC01 100 156 078 28CMC02 200 156 078 28CMC03 300 156 078 28CMC04 400 156 078 28CMD01 100 164 069 25CMD02 200 164 069 25CMD03 300 164 069 25CMD04 400 164 069 25TZA01 100 147 089 32TZA02 200 147 089 32TZA03 300 147 089 32TZA04 400 147 089 32TZB01 100 151 083 30TZB02 200 151 083 30TZB03 300 151 083 30TZB04 400 151 083 30TZC01 100 164 069 25TZC02 200 164 069 25TZC03 300 164 069 25TZC04 400 164 069 25p0 means initial confining pressure ρd means dry density e0 means initial void ratio and w0 means initial moisture content

100kPa200kPa

300kPa400kPa

0

300

600

900

1200

1500

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(a)

O

AB C

0

100

200

300

400

500

(σ1ndash

σ 3)

kPa

100kPa200kPa

300kPa400kPa

ε ()4 62 8 10 12 14 160

(b)

Figure 5 Stress-strain behaviour under four confining pressures (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 5

Figure 7 coral mud has a better permeability with a higherdissipation rate of the pore pressure Figure 8 presents thepore pressure at the shear stage For Taizhou soil the poresare similar to those of common clay that gradually develop toa peak after ε 2when the cement material is extruded andthe particles are in direct contact During the whole processthe pressures are above zero and are positively correlatedwith the confining pressure and the difference value under

adjacent confining pressure is up to 80 kPa In contrast thepore pressure of the coral mud first rises to a positive peak ina small range and then decreases to a stable negative valuee reason for the difference may be the mineral compo-sition Calcium carbonate is the main substance that makesup the coral mud whose coefficient of permeability is higherthan that of common clay erefore the pore pressure ofcoral mud is hard to accumulate

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

200

400

600

800

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(a)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(b)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

(c)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

600

1200

1800

2400

(σ1ndash

σ 3)

kPa

(d)

Figure 6 Stress-strain behaviour at different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Table 4 Coulomb-molar parameters of coral mud and Taizhou soil

Type c1 (kPa) c2 (kPa) c3 (kPa) c4 (kPa) c5 (kPa) c6 (kPa) c (kPa) φ1 φ2 φ3 φ4 φ5 φ6 φCoral mud 12265 12391 6885 16834 294 159 8138 23deg 21deg 33deg 18deg 37deg 46deg 279degTaizhou soil 6762 4616 5479 201 363 1503 5365 11deg 17deg 15deg 22deg 16deg 9deg 150deg

6 Advances in Civil Engineering

322 Effects of the Initial Void Ratio e pore pressureswith different e0 values are shown in Figure 9 e peak porepressure of both samples increases with increasing e0 butcoral mud has a larger difference value with respect to thepore pressure as e0 changes

e pore pressure coefficient of sample failure isexpressed as Af to represent the final failure state e re-lationships between Af and e0 are shown in Figure 10 It isclear that Af and e0 are linearly correlated but the effect of e0varies under different p0 values When p0 100 kPa e0 hasthe greatest effect and Af tends to be stable with increasingp0 demonstrating that the two factors are not independentof each other in terms of their effects on Af

33 Effective Stress Path In conventional triaxial tests theeffective stress path is usually expressed in the prsquo-q planewhere prsquo ismean effective stress and q is deviatoric stresses

pprime σ1 + 2σ3

3minus u

q

3+ σ1 minus u

q 12

radic

σ1prime minus σ2prime( 11138572

+ σ2prime minus σ3prime( 11138572

+ σ3prime minus σ1prime( 11138572

1113969 (1)

As shown in Figure 11 because of the unique porepressure developments during undrained shearing the ef-fective stress path of coral mud is unlike the normallyconsolidated clay curve which develops to the left [28] or the

01 1 10 100 10000

150

300

450

600

lgt (min)

u (k

Pa)

σ3 = 400kPaσ3 = 400kPaσ3 = 200kPaσ3 = 200kPa

Taizhou soilCoral mudTaizhou soilCoral mud

Figure 7 Pore pressure dissipation curve at the consolidation stage

u (k

Pa)

0

100

200

300

100kPa (Taizhou soil) 100kPa (coral mud)200kPa (Taizhou soil) 200kPa (coral mud)300kPa (Taizhou soil) 300kPa (coral mud)400kPa (Taizhou soil) 400kPa (coral mud)

0 2 4 6 8 10 12 14 16ndash2ε ()

Figure 8 Pore pressures under different confining pressures

Advances in Civil Engineering 7

general silt with an ldquoSrdquo curve [29] Additionally effectivestress path is also not the same as the curve of over-consolidated clay which obviously develops from right toleft [30]is path is similar to the total stress path curve anddevelops in a straight line Although the stress path curvesunder different confining pressures are always similar asconfining pressure does not change the critical state of thesoil mass compared with Taizhou soil the stress path ofcoral mud is less affected e surge of pore pressure onlyexists at e0 089 and p0 400 kPa in the early shear phasewhich causes a significant inflection point and the

inclination of other stress path curves of coral mud is almostequal

Drawing the critical state line (CSL) according to thestress path as shown in Figure 12 there is a good linearrelationship between qcs and pcsacute and it passes through theorigin which is consistent with the studies of other scholarsFigure 12 also shows the effective stress ratio Mcs at thecritical state It can be concluded that the Mcs value ofTaizhou soil declines with increasing e0 while that of coralmud first decreases and then slightly increases with in-creasing e0 corresponding to the testing results that when

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120u

(kPa

)

(a)

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120

160

200

u (k

Pa)

(b)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(c)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

300

350

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(d)

Figure 9 Pore pressures with different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

8 Advances in Civil Engineering

e0 089 the deviatoric stress of coral mud continues toincrease and finally is higher than the samples of e0 083

34 Friction Angle e mobilized friction angle φm underthe triaxial compression condition is defined as [31]

sinφm 3η

6 + η (2)

where η is defined as the ratio of the deviatoric stress q to theeffective mean stress prsquo

065 070 075 080 085 090

ndash008

ndash004

000

004

Af = 0268e0 ndash 0264 (simulation)Af = 0162e0 ndash 0153 (simulation)Af = 0162e0 ndash 0143 (simulation)Af = 0117e0 ndash 0097 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

(a)

Af = 1128e0 ndash 0692 (simulation)Af = 0977e0 ndash 0390 (simulation)Af = 0812e0 ndash 0258 (simulation)Af = 0883e0 ndash 0244 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

065 070 075 080 085 09000

01

02

03

04

05

06

07

08

(b)

Figure 10 Relationship between af and e0 (a) coral mud and (b) Taizhou soil

0 300 600 900pprime(kPa)

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

0

500

1000

1500

2000

2500

q (k

Pa)

(a)

pprime(kPa)

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

0 200 400 6000

300

600

900

q (k

Pa)

(b)

Figure 11 Effective stress paths with different initial void ratios (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 9

η q

pprime (3)

e critical state friction angle φcs under the triaxialcompression condition can be defined as

sinφcs 3ηcs

6 + ηcs (4)

where ηcs is critical state stress ratioe test data show that ηonly changes slightly when the strain is 15 According tothe critical state theory [32] the stress state under this straincould be considered a critical state

e peak state friction angle φps is defined as

sinφps 3ηps

6 + ηps (5)

where ηps is the peak state stress ratioFigure 13 presents the mobilized friction angle of coral

mud and Taizhou soil at different initial void ratios andpressures e values of φcs and φps are shown in Table 5Similar to the stress-strain relationship the mobilizedfriction angle-strain relationship of coral mud presents aplatform shape and when e0 089 the curve has theproperty of overpenetration while the other curves decreasewith an increase in the initial void ratio Most φps valuesoverlap with φcs and the remainder gradually approach thecritical state φcs of coral mud is much greater than that ofTaizhou soil and with increasing confining pressure φcs ofcoral mud tends to disperse while the Taizhou soil tends tobe dense indicating that the initial void ratio has a minoreffect on φcs of coral mud when the confining pressure is low

As shown in Figure 14 φcs of Taizhou soil decreases firstand then tends to be stable with an increase in the confiningpressure which indicates that an increase in the confining

pressure gradually has less influence on the critical frictionangle of Taizhou soil Figure 15(b) also proves this con-clusion as the 300 kPa and 400 kPa curves almost coincideIn contrast the confining pressure is an important pa-rameter on φcs of coral mud With an increase in theconfining pressure φcs first decreases and then increaseswhen e0 078 and e0 083 first increases then decreasesand then increases when e0 069 and first decreases thenincreases and then decreases when e0 089 Figure 15(a)illustrates that at 100 kPa the effect of the initial void ratio isminor as the curve approximates a straight line which isconsistent with the phenomenon of the high coincidence ofφcs in Figure 13(a) Under the other confining pressures φcsof coral mud first decreases and then increases with theincrease in e0p0 is the initial confining pressure e0 is theinitial void ratio φcs-c is the critical state friction angle ofcoral mud φps-c is the peak state friction angle of coral mudφcs-T is the critical state friction angle of Taizhou soil andφps-T is the peak state friction angle of Taizhou soil

35Modulus e initial elastic modulus E0i is an importantparameter indicating the deformation behaviour of coralmud It can be expressed as [33]

E0i qα

εα (6)

where εa means the axial strain constrained within 01 forthe initial slope of the stress-strain curve where the de-formation is supposed to be elastic

E50 is the ratio of the stress of half of the peak stress of soilto the corresponding strain [34] which is defined as

E50 05qps

εaps (7)

0 400 800 1200

e0 = 069e0 = 078e0 = 083e0 = 089

M = 1722M = 1675M = 1539M = 1655

pprime(kPa)

0

400

800

1200

1600

q (k

Pa)

(a)

e0 = 069e0 = 083e0 = 089

M = 1481M = 1426M = 1373

0 200 400pprime(kPa)

0

200

400

600

800

q (k

Pa)

(b)

Figure 12 Mcs with different initial void ratios (a) coral mud and (b) Taizhou soil

10 Advances in Civil Engineering

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

of 100 kPa 200 kPa 300 kPa and 400 kPa (backpressure50 kPa) e stress-strain behaviours are given in Figure 5e strengths of the two soil samples both significantlyincrease with increasing confining pressure especially thestrength of the coral mud of adjacent confining pressurewhich increases by nearly 500 kPae strength of coral mudwas much higher than that of Taizhou soil under the same

confining pressure For a quantitative comparison we cal-culated the c and φ of the two soil samples and calculated themean values (Table 4) e mean internal friction angle ofTaizhou soil is 15deg in line with the values of engineeringexperience which is generally 15deg to 25deg but far smaller thanthose of coral mudis result could be attributed to the slip-like structure and unique physicochemical properties of

Perc

enta

ge fi

ner

Coral mudTaizhou soil

100 10 1 011000Particle size (μm)

0

20

40

60

80

100

Figure 2 Particle size distribution

Table 2 Basic characteristics of coral mud and Taizhou soil

Type Specific gravity Gs Liquid limit wL Plastic limit wp Plastic index Ip

Coral mud 277 338 23 108Taizhou soil 271 334 224 110

(a) (b)

Figure 1 Images of (a) coral mud and (b) Taizhou soil

Table 1 Mineral composition of coral mud and Taizhou soil

TypeMineral composition Chemical component

Percentage mass of various minerals (Wt ) Percentage of mass of each element (Wt )

Coral mud Biogenic calcium carbonate (Mg129Ca871) CO3 Ca Mg O C606 394 387 1 483 121

Taizhou soil SiO2 (Mg003Ca097) CO3 Ca Si O C927 73 29 433 529 09

Advances in Civil Engineering 3

coral mud making the bite force generated by interparticleembedding large and strong

In addition the stress-strain growth trends of the two arealso significantly different e stress of coral mud increasesrapidly at the initial stage of shear when ε is 1 the stressreaches approximately 23 of the shear strength and theelastic modulus in the early stage is positively correlated withthe confining pressure In contrast only when the confiningpressure is 100 kPa does the Taizhou soil curve show aplatform e stress under other confining pressures sta-bilizes or even slightly decreases at approximately 50 kPabefore ε 2 and increases sharply between 2 and 3After ε 3 the stress shows an increase with a steady ratewhose amplitude accounts for 14 to 12 of the total stress

From a microperspective this increase could be a resultof various particle contact responses Previous studies[25 26] have shown that the contact between particles in-cludes frictional contact and cemented contact e contactof Taizhou soil is cemented contact and its stress-strainbehaviour can be divided into the following three stages (1)the OA stage where the stress increases linearly (2) the ABstage where cement begins to break or extrude in which thestress develops smoothly or even declines at this stage and(3) the BC stage where particles come into direct contacte stress increases rapidly at this stage and its growth rate

is greater than that at the OA stage Due to the lack ofcementing materials coral mud skips the OA and AB stagesIts irregular particles come into direct contact from thebeginning and the stress levels off after a rapid increase

312 Effects of the Initial Void Ratio Figure 6 shows thestress-strain relationship with different initial void ratios ofcoral mud and Taizhou soil For Taizhou soil the stress-strain behaviours of different e0 values are roughly the sameas the deviatoric stress rising by a small margin with adecrease in e0 In addition the strain when the stress surgesdeclines with decreasing e0 which means that the cement ismore likely to be extruded and the particles are more likelyto come into direct contact with each other under high drydensity conditions In contrast the coral mud is moresignificantly affected manifested as the diverse variationtrend as well as the D-value which can reach 500 kPa Whene0 089 the stress-strain plot is obviously different in that itis an enhanced curve whose peak stress is higher thane0 083 under different confining pressures From theperspective of elastoplasticity when the pressure increasesthe coral mud with a large porosity transits from the elasticstage to the ideal plastic stage where part of the structure isbroken Its particles are more prone to particle dislocation

(a) (b)

Figure 3 SEM image of the testing materials (a) coral mud and (b) Taizhou soil

0 20 40 60 8004

06

08

10

R

Coral mudTaizhou soil

(a)

Coral mudTaizhou soil

0 20 40 60 800

1

2

3

4

5

T

(b)

Figure 4 Shape parameters of the testing materials (a) circular degree and (b) ring diameter ratio

4 Advances in Civil Engineering

and rearrangement which fills the pores and brings about agrowth in the shear strength when e0 089 [27] Taizhou soilhas no such feature owing to its shape and cementingsubstance which do not facilitate maloperation and oc-clusion friction compared with needle-like particles [28]

32 Pore Pressure Development

321 Effects of the Initial Confining Pressure In this part wecontrolled e0 069 to study the development law of the porepressure under different confining pressures As shown in

Table 3 Program of CU shear tests

Number p0 (kPa) ρd (gcm3) e0 w0 ()

CMA01 100 147 089 32CMA02 200 147 089 32CMA03 300 147 089 32CMA04 400 147 089 32CMA05 600 147 089 32CMB01 100 151 083 30CMB02 200 151 083 30CMB03 300 151 083 30CMB04 400 151 083 30CMC01 100 156 078 28CMC02 200 156 078 28CMC03 300 156 078 28CMC04 400 156 078 28CMD01 100 164 069 25CMD02 200 164 069 25CMD03 300 164 069 25CMD04 400 164 069 25TZA01 100 147 089 32TZA02 200 147 089 32TZA03 300 147 089 32TZA04 400 147 089 32TZB01 100 151 083 30TZB02 200 151 083 30TZB03 300 151 083 30TZB04 400 151 083 30TZC01 100 164 069 25TZC02 200 164 069 25TZC03 300 164 069 25TZC04 400 164 069 25p0 means initial confining pressure ρd means dry density e0 means initial void ratio and w0 means initial moisture content

100kPa200kPa

300kPa400kPa

0

300

600

900

1200

1500

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(a)

O

AB C

0

100

200

300

400

500

(σ1ndash

σ 3)

kPa

100kPa200kPa

300kPa400kPa

ε ()4 62 8 10 12 14 160

(b)

Figure 5 Stress-strain behaviour under four confining pressures (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 5

Figure 7 coral mud has a better permeability with a higherdissipation rate of the pore pressure Figure 8 presents thepore pressure at the shear stage For Taizhou soil the poresare similar to those of common clay that gradually develop toa peak after ε 2when the cement material is extruded andthe particles are in direct contact During the whole processthe pressures are above zero and are positively correlatedwith the confining pressure and the difference value under

adjacent confining pressure is up to 80 kPa In contrast thepore pressure of the coral mud first rises to a positive peak ina small range and then decreases to a stable negative valuee reason for the difference may be the mineral compo-sition Calcium carbonate is the main substance that makesup the coral mud whose coefficient of permeability is higherthan that of common clay erefore the pore pressure ofcoral mud is hard to accumulate

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

200

400

600

800

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(a)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(b)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

(c)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

600

1200

1800

2400

(σ1ndash

σ 3)

kPa

(d)

Figure 6 Stress-strain behaviour at different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Table 4 Coulomb-molar parameters of coral mud and Taizhou soil

Type c1 (kPa) c2 (kPa) c3 (kPa) c4 (kPa) c5 (kPa) c6 (kPa) c (kPa) φ1 φ2 φ3 φ4 φ5 φ6 φCoral mud 12265 12391 6885 16834 294 159 8138 23deg 21deg 33deg 18deg 37deg 46deg 279degTaizhou soil 6762 4616 5479 201 363 1503 5365 11deg 17deg 15deg 22deg 16deg 9deg 150deg

6 Advances in Civil Engineering

322 Effects of the Initial Void Ratio e pore pressureswith different e0 values are shown in Figure 9 e peak porepressure of both samples increases with increasing e0 butcoral mud has a larger difference value with respect to thepore pressure as e0 changes

e pore pressure coefficient of sample failure isexpressed as Af to represent the final failure state e re-lationships between Af and e0 are shown in Figure 10 It isclear that Af and e0 are linearly correlated but the effect of e0varies under different p0 values When p0 100 kPa e0 hasthe greatest effect and Af tends to be stable with increasingp0 demonstrating that the two factors are not independentof each other in terms of their effects on Af

33 Effective Stress Path In conventional triaxial tests theeffective stress path is usually expressed in the prsquo-q planewhere prsquo ismean effective stress and q is deviatoric stresses

pprime σ1 + 2σ3

3minus u

q

3+ σ1 minus u

q 12

radic

σ1prime minus σ2prime( 11138572

+ σ2prime minus σ3prime( 11138572

+ σ3prime minus σ1prime( 11138572

1113969 (1)

As shown in Figure 11 because of the unique porepressure developments during undrained shearing the ef-fective stress path of coral mud is unlike the normallyconsolidated clay curve which develops to the left [28] or the

01 1 10 100 10000

150

300

450

600

lgt (min)

u (k

Pa)

σ3 = 400kPaσ3 = 400kPaσ3 = 200kPaσ3 = 200kPa

Taizhou soilCoral mudTaizhou soilCoral mud

Figure 7 Pore pressure dissipation curve at the consolidation stage

u (k

Pa)

0

100

200

300

100kPa (Taizhou soil) 100kPa (coral mud)200kPa (Taizhou soil) 200kPa (coral mud)300kPa (Taizhou soil) 300kPa (coral mud)400kPa (Taizhou soil) 400kPa (coral mud)

0 2 4 6 8 10 12 14 16ndash2ε ()

Figure 8 Pore pressures under different confining pressures

Advances in Civil Engineering 7

general silt with an ldquoSrdquo curve [29] Additionally effectivestress path is also not the same as the curve of over-consolidated clay which obviously develops from right toleft [30]is path is similar to the total stress path curve anddevelops in a straight line Although the stress path curvesunder different confining pressures are always similar asconfining pressure does not change the critical state of thesoil mass compared with Taizhou soil the stress path ofcoral mud is less affected e surge of pore pressure onlyexists at e0 089 and p0 400 kPa in the early shear phasewhich causes a significant inflection point and the

inclination of other stress path curves of coral mud is almostequal

Drawing the critical state line (CSL) according to thestress path as shown in Figure 12 there is a good linearrelationship between qcs and pcsacute and it passes through theorigin which is consistent with the studies of other scholarsFigure 12 also shows the effective stress ratio Mcs at thecritical state It can be concluded that the Mcs value ofTaizhou soil declines with increasing e0 while that of coralmud first decreases and then slightly increases with in-creasing e0 corresponding to the testing results that when

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120u

(kPa

)

(a)

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120

160

200

u (k

Pa)

(b)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(c)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

300

350

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(d)

Figure 9 Pore pressures with different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

8 Advances in Civil Engineering

e0 089 the deviatoric stress of coral mud continues toincrease and finally is higher than the samples of e0 083

34 Friction Angle e mobilized friction angle φm underthe triaxial compression condition is defined as [31]

sinφm 3η

6 + η (2)

where η is defined as the ratio of the deviatoric stress q to theeffective mean stress prsquo

065 070 075 080 085 090

ndash008

ndash004

000

004

Af = 0268e0 ndash 0264 (simulation)Af = 0162e0 ndash 0153 (simulation)Af = 0162e0 ndash 0143 (simulation)Af = 0117e0 ndash 0097 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

(a)

Af = 1128e0 ndash 0692 (simulation)Af = 0977e0 ndash 0390 (simulation)Af = 0812e0 ndash 0258 (simulation)Af = 0883e0 ndash 0244 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

065 070 075 080 085 09000

01

02

03

04

05

06

07

08

(b)

Figure 10 Relationship between af and e0 (a) coral mud and (b) Taizhou soil

0 300 600 900pprime(kPa)

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

0

500

1000

1500

2000

2500

q (k

Pa)

(a)

pprime(kPa)

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

0 200 400 6000

300

600

900

q (k

Pa)

(b)

Figure 11 Effective stress paths with different initial void ratios (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 9

η q

pprime (3)

e critical state friction angle φcs under the triaxialcompression condition can be defined as

sinφcs 3ηcs

6 + ηcs (4)

where ηcs is critical state stress ratioe test data show that ηonly changes slightly when the strain is 15 According tothe critical state theory [32] the stress state under this straincould be considered a critical state

e peak state friction angle φps is defined as

sinφps 3ηps

6 + ηps (5)

where ηps is the peak state stress ratioFigure 13 presents the mobilized friction angle of coral

mud and Taizhou soil at different initial void ratios andpressures e values of φcs and φps are shown in Table 5Similar to the stress-strain relationship the mobilizedfriction angle-strain relationship of coral mud presents aplatform shape and when e0 089 the curve has theproperty of overpenetration while the other curves decreasewith an increase in the initial void ratio Most φps valuesoverlap with φcs and the remainder gradually approach thecritical state φcs of coral mud is much greater than that ofTaizhou soil and with increasing confining pressure φcs ofcoral mud tends to disperse while the Taizhou soil tends tobe dense indicating that the initial void ratio has a minoreffect on φcs of coral mud when the confining pressure is low

As shown in Figure 14 φcs of Taizhou soil decreases firstand then tends to be stable with an increase in the confiningpressure which indicates that an increase in the confining

pressure gradually has less influence on the critical frictionangle of Taizhou soil Figure 15(b) also proves this con-clusion as the 300 kPa and 400 kPa curves almost coincideIn contrast the confining pressure is an important pa-rameter on φcs of coral mud With an increase in theconfining pressure φcs first decreases and then increaseswhen e0 078 and e0 083 first increases then decreasesand then increases when e0 069 and first decreases thenincreases and then decreases when e0 089 Figure 15(a)illustrates that at 100 kPa the effect of the initial void ratio isminor as the curve approximates a straight line which isconsistent with the phenomenon of the high coincidence ofφcs in Figure 13(a) Under the other confining pressures φcsof coral mud first decreases and then increases with theincrease in e0p0 is the initial confining pressure e0 is theinitial void ratio φcs-c is the critical state friction angle ofcoral mud φps-c is the peak state friction angle of coral mudφcs-T is the critical state friction angle of Taizhou soil andφps-T is the peak state friction angle of Taizhou soil

35Modulus e initial elastic modulus E0i is an importantparameter indicating the deformation behaviour of coralmud It can be expressed as [33]

E0i qα

εα (6)

where εa means the axial strain constrained within 01 forthe initial slope of the stress-strain curve where the de-formation is supposed to be elastic

E50 is the ratio of the stress of half of the peak stress of soilto the corresponding strain [34] which is defined as

E50 05qps

εaps (7)

0 400 800 1200

e0 = 069e0 = 078e0 = 083e0 = 089

M = 1722M = 1675M = 1539M = 1655

pprime(kPa)

0

400

800

1200

1600

q (k

Pa)

(a)

e0 = 069e0 = 083e0 = 089

M = 1481M = 1426M = 1373

0 200 400pprime(kPa)

0

200

400

600

800

q (k

Pa)

(b)

Figure 12 Mcs with different initial void ratios (a) coral mud and (b) Taizhou soil

10 Advances in Civil Engineering

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

coral mud making the bite force generated by interparticleembedding large and strong

In addition the stress-strain growth trends of the two arealso significantly different e stress of coral mud increasesrapidly at the initial stage of shear when ε is 1 the stressreaches approximately 23 of the shear strength and theelastic modulus in the early stage is positively correlated withthe confining pressure In contrast only when the confiningpressure is 100 kPa does the Taizhou soil curve show aplatform e stress under other confining pressures sta-bilizes or even slightly decreases at approximately 50 kPabefore ε 2 and increases sharply between 2 and 3After ε 3 the stress shows an increase with a steady ratewhose amplitude accounts for 14 to 12 of the total stress

From a microperspective this increase could be a resultof various particle contact responses Previous studies[25 26] have shown that the contact between particles in-cludes frictional contact and cemented contact e contactof Taizhou soil is cemented contact and its stress-strainbehaviour can be divided into the following three stages (1)the OA stage where the stress increases linearly (2) the ABstage where cement begins to break or extrude in which thestress develops smoothly or even declines at this stage and(3) the BC stage where particles come into direct contacte stress increases rapidly at this stage and its growth rate

is greater than that at the OA stage Due to the lack ofcementing materials coral mud skips the OA and AB stagesIts irregular particles come into direct contact from thebeginning and the stress levels off after a rapid increase

312 Effects of the Initial Void Ratio Figure 6 shows thestress-strain relationship with different initial void ratios ofcoral mud and Taizhou soil For Taizhou soil the stress-strain behaviours of different e0 values are roughly the sameas the deviatoric stress rising by a small margin with adecrease in e0 In addition the strain when the stress surgesdeclines with decreasing e0 which means that the cement ismore likely to be extruded and the particles are more likelyto come into direct contact with each other under high drydensity conditions In contrast the coral mud is moresignificantly affected manifested as the diverse variationtrend as well as the D-value which can reach 500 kPa Whene0 089 the stress-strain plot is obviously different in that itis an enhanced curve whose peak stress is higher thane0 083 under different confining pressures From theperspective of elastoplasticity when the pressure increasesthe coral mud with a large porosity transits from the elasticstage to the ideal plastic stage where part of the structure isbroken Its particles are more prone to particle dislocation

(a) (b)

Figure 3 SEM image of the testing materials (a) coral mud and (b) Taizhou soil

0 20 40 60 8004

06

08

10

R

Coral mudTaizhou soil

(a)

Coral mudTaizhou soil

0 20 40 60 800

1

2

3

4

5

T

(b)

Figure 4 Shape parameters of the testing materials (a) circular degree and (b) ring diameter ratio

4 Advances in Civil Engineering

and rearrangement which fills the pores and brings about agrowth in the shear strength when e0 089 [27] Taizhou soilhas no such feature owing to its shape and cementingsubstance which do not facilitate maloperation and oc-clusion friction compared with needle-like particles [28]

32 Pore Pressure Development

321 Effects of the Initial Confining Pressure In this part wecontrolled e0 069 to study the development law of the porepressure under different confining pressures As shown in

Table 3 Program of CU shear tests

Number p0 (kPa) ρd (gcm3) e0 w0 ()

CMA01 100 147 089 32CMA02 200 147 089 32CMA03 300 147 089 32CMA04 400 147 089 32CMA05 600 147 089 32CMB01 100 151 083 30CMB02 200 151 083 30CMB03 300 151 083 30CMB04 400 151 083 30CMC01 100 156 078 28CMC02 200 156 078 28CMC03 300 156 078 28CMC04 400 156 078 28CMD01 100 164 069 25CMD02 200 164 069 25CMD03 300 164 069 25CMD04 400 164 069 25TZA01 100 147 089 32TZA02 200 147 089 32TZA03 300 147 089 32TZA04 400 147 089 32TZB01 100 151 083 30TZB02 200 151 083 30TZB03 300 151 083 30TZB04 400 151 083 30TZC01 100 164 069 25TZC02 200 164 069 25TZC03 300 164 069 25TZC04 400 164 069 25p0 means initial confining pressure ρd means dry density e0 means initial void ratio and w0 means initial moisture content

100kPa200kPa

300kPa400kPa

0

300

600

900

1200

1500

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(a)

O

AB C

0

100

200

300

400

500

(σ1ndash

σ 3)

kPa

100kPa200kPa

300kPa400kPa

ε ()4 62 8 10 12 14 160

(b)

Figure 5 Stress-strain behaviour under four confining pressures (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 5

Figure 7 coral mud has a better permeability with a higherdissipation rate of the pore pressure Figure 8 presents thepore pressure at the shear stage For Taizhou soil the poresare similar to those of common clay that gradually develop toa peak after ε 2when the cement material is extruded andthe particles are in direct contact During the whole processthe pressures are above zero and are positively correlatedwith the confining pressure and the difference value under

adjacent confining pressure is up to 80 kPa In contrast thepore pressure of the coral mud first rises to a positive peak ina small range and then decreases to a stable negative valuee reason for the difference may be the mineral compo-sition Calcium carbonate is the main substance that makesup the coral mud whose coefficient of permeability is higherthan that of common clay erefore the pore pressure ofcoral mud is hard to accumulate

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

200

400

600

800

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(a)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(b)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

(c)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

600

1200

1800

2400

(σ1ndash

σ 3)

kPa

(d)

Figure 6 Stress-strain behaviour at different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Table 4 Coulomb-molar parameters of coral mud and Taizhou soil

Type c1 (kPa) c2 (kPa) c3 (kPa) c4 (kPa) c5 (kPa) c6 (kPa) c (kPa) φ1 φ2 φ3 φ4 φ5 φ6 φCoral mud 12265 12391 6885 16834 294 159 8138 23deg 21deg 33deg 18deg 37deg 46deg 279degTaizhou soil 6762 4616 5479 201 363 1503 5365 11deg 17deg 15deg 22deg 16deg 9deg 150deg

6 Advances in Civil Engineering

322 Effects of the Initial Void Ratio e pore pressureswith different e0 values are shown in Figure 9 e peak porepressure of both samples increases with increasing e0 butcoral mud has a larger difference value with respect to thepore pressure as e0 changes

e pore pressure coefficient of sample failure isexpressed as Af to represent the final failure state e re-lationships between Af and e0 are shown in Figure 10 It isclear that Af and e0 are linearly correlated but the effect of e0varies under different p0 values When p0 100 kPa e0 hasthe greatest effect and Af tends to be stable with increasingp0 demonstrating that the two factors are not independentof each other in terms of their effects on Af

33 Effective Stress Path In conventional triaxial tests theeffective stress path is usually expressed in the prsquo-q planewhere prsquo ismean effective stress and q is deviatoric stresses

pprime σ1 + 2σ3

3minus u

q

3+ σ1 minus u

q 12

radic

σ1prime minus σ2prime( 11138572

+ σ2prime minus σ3prime( 11138572

+ σ3prime minus σ1prime( 11138572

1113969 (1)

As shown in Figure 11 because of the unique porepressure developments during undrained shearing the ef-fective stress path of coral mud is unlike the normallyconsolidated clay curve which develops to the left [28] or the

01 1 10 100 10000

150

300

450

600

lgt (min)

u (k

Pa)

σ3 = 400kPaσ3 = 400kPaσ3 = 200kPaσ3 = 200kPa

Taizhou soilCoral mudTaizhou soilCoral mud

Figure 7 Pore pressure dissipation curve at the consolidation stage

u (k

Pa)

0

100

200

300

100kPa (Taizhou soil) 100kPa (coral mud)200kPa (Taizhou soil) 200kPa (coral mud)300kPa (Taizhou soil) 300kPa (coral mud)400kPa (Taizhou soil) 400kPa (coral mud)

0 2 4 6 8 10 12 14 16ndash2ε ()

Figure 8 Pore pressures under different confining pressures

Advances in Civil Engineering 7

general silt with an ldquoSrdquo curve [29] Additionally effectivestress path is also not the same as the curve of over-consolidated clay which obviously develops from right toleft [30]is path is similar to the total stress path curve anddevelops in a straight line Although the stress path curvesunder different confining pressures are always similar asconfining pressure does not change the critical state of thesoil mass compared with Taizhou soil the stress path ofcoral mud is less affected e surge of pore pressure onlyexists at e0 089 and p0 400 kPa in the early shear phasewhich causes a significant inflection point and the

inclination of other stress path curves of coral mud is almostequal

Drawing the critical state line (CSL) according to thestress path as shown in Figure 12 there is a good linearrelationship between qcs and pcsacute and it passes through theorigin which is consistent with the studies of other scholarsFigure 12 also shows the effective stress ratio Mcs at thecritical state It can be concluded that the Mcs value ofTaizhou soil declines with increasing e0 while that of coralmud first decreases and then slightly increases with in-creasing e0 corresponding to the testing results that when

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120u

(kPa

)

(a)

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120

160

200

u (k

Pa)

(b)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(c)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

300

350

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(d)

Figure 9 Pore pressures with different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

8 Advances in Civil Engineering

e0 089 the deviatoric stress of coral mud continues toincrease and finally is higher than the samples of e0 083

34 Friction Angle e mobilized friction angle φm underthe triaxial compression condition is defined as [31]

sinφm 3η

6 + η (2)

where η is defined as the ratio of the deviatoric stress q to theeffective mean stress prsquo

065 070 075 080 085 090

ndash008

ndash004

000

004

Af = 0268e0 ndash 0264 (simulation)Af = 0162e0 ndash 0153 (simulation)Af = 0162e0 ndash 0143 (simulation)Af = 0117e0 ndash 0097 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

(a)

Af = 1128e0 ndash 0692 (simulation)Af = 0977e0 ndash 0390 (simulation)Af = 0812e0 ndash 0258 (simulation)Af = 0883e0 ndash 0244 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

065 070 075 080 085 09000

01

02

03

04

05

06

07

08

(b)

Figure 10 Relationship between af and e0 (a) coral mud and (b) Taizhou soil

0 300 600 900pprime(kPa)

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

0

500

1000

1500

2000

2500

q (k

Pa)

(a)

pprime(kPa)

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

0 200 400 6000

300

600

900

q (k

Pa)

(b)

Figure 11 Effective stress paths with different initial void ratios (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 9

η q

pprime (3)

e critical state friction angle φcs under the triaxialcompression condition can be defined as

sinφcs 3ηcs

6 + ηcs (4)

where ηcs is critical state stress ratioe test data show that ηonly changes slightly when the strain is 15 According tothe critical state theory [32] the stress state under this straincould be considered a critical state

e peak state friction angle φps is defined as

sinφps 3ηps

6 + ηps (5)

where ηps is the peak state stress ratioFigure 13 presents the mobilized friction angle of coral

mud and Taizhou soil at different initial void ratios andpressures e values of φcs and φps are shown in Table 5Similar to the stress-strain relationship the mobilizedfriction angle-strain relationship of coral mud presents aplatform shape and when e0 089 the curve has theproperty of overpenetration while the other curves decreasewith an increase in the initial void ratio Most φps valuesoverlap with φcs and the remainder gradually approach thecritical state φcs of coral mud is much greater than that ofTaizhou soil and with increasing confining pressure φcs ofcoral mud tends to disperse while the Taizhou soil tends tobe dense indicating that the initial void ratio has a minoreffect on φcs of coral mud when the confining pressure is low

As shown in Figure 14 φcs of Taizhou soil decreases firstand then tends to be stable with an increase in the confiningpressure which indicates that an increase in the confining

pressure gradually has less influence on the critical frictionangle of Taizhou soil Figure 15(b) also proves this con-clusion as the 300 kPa and 400 kPa curves almost coincideIn contrast the confining pressure is an important pa-rameter on φcs of coral mud With an increase in theconfining pressure φcs first decreases and then increaseswhen e0 078 and e0 083 first increases then decreasesand then increases when e0 069 and first decreases thenincreases and then decreases when e0 089 Figure 15(a)illustrates that at 100 kPa the effect of the initial void ratio isminor as the curve approximates a straight line which isconsistent with the phenomenon of the high coincidence ofφcs in Figure 13(a) Under the other confining pressures φcsof coral mud first decreases and then increases with theincrease in e0p0 is the initial confining pressure e0 is theinitial void ratio φcs-c is the critical state friction angle ofcoral mud φps-c is the peak state friction angle of coral mudφcs-T is the critical state friction angle of Taizhou soil andφps-T is the peak state friction angle of Taizhou soil

35Modulus e initial elastic modulus E0i is an importantparameter indicating the deformation behaviour of coralmud It can be expressed as [33]

E0i qα

εα (6)

where εa means the axial strain constrained within 01 forthe initial slope of the stress-strain curve where the de-formation is supposed to be elastic

E50 is the ratio of the stress of half of the peak stress of soilto the corresponding strain [34] which is defined as

E50 05qps

εaps (7)

0 400 800 1200

e0 = 069e0 = 078e0 = 083e0 = 089

M = 1722M = 1675M = 1539M = 1655

pprime(kPa)

0

400

800

1200

1600

q (k

Pa)

(a)

e0 = 069e0 = 083e0 = 089

M = 1481M = 1426M = 1373

0 200 400pprime(kPa)

0

200

400

600

800

q (k

Pa)

(b)

Figure 12 Mcs with different initial void ratios (a) coral mud and (b) Taizhou soil

10 Advances in Civil Engineering

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

and rearrangement which fills the pores and brings about agrowth in the shear strength when e0 089 [27] Taizhou soilhas no such feature owing to its shape and cementingsubstance which do not facilitate maloperation and oc-clusion friction compared with needle-like particles [28]

32 Pore Pressure Development

321 Effects of the Initial Confining Pressure In this part wecontrolled e0 069 to study the development law of the porepressure under different confining pressures As shown in

Table 3 Program of CU shear tests

Number p0 (kPa) ρd (gcm3) e0 w0 ()

CMA01 100 147 089 32CMA02 200 147 089 32CMA03 300 147 089 32CMA04 400 147 089 32CMA05 600 147 089 32CMB01 100 151 083 30CMB02 200 151 083 30CMB03 300 151 083 30CMB04 400 151 083 30CMC01 100 156 078 28CMC02 200 156 078 28CMC03 300 156 078 28CMC04 400 156 078 28CMD01 100 164 069 25CMD02 200 164 069 25CMD03 300 164 069 25CMD04 400 164 069 25TZA01 100 147 089 32TZA02 200 147 089 32TZA03 300 147 089 32TZA04 400 147 089 32TZB01 100 151 083 30TZB02 200 151 083 30TZB03 300 151 083 30TZB04 400 151 083 30TZC01 100 164 069 25TZC02 200 164 069 25TZC03 300 164 069 25TZC04 400 164 069 25p0 means initial confining pressure ρd means dry density e0 means initial void ratio and w0 means initial moisture content

100kPa200kPa

300kPa400kPa

0

300

600

900

1200

1500

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(a)

O

AB C

0

100

200

300

400

500

(σ1ndash

σ 3)

kPa

100kPa200kPa

300kPa400kPa

ε ()4 62 8 10 12 14 160

(b)

Figure 5 Stress-strain behaviour under four confining pressures (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 5

Figure 7 coral mud has a better permeability with a higherdissipation rate of the pore pressure Figure 8 presents thepore pressure at the shear stage For Taizhou soil the poresare similar to those of common clay that gradually develop toa peak after ε 2when the cement material is extruded andthe particles are in direct contact During the whole processthe pressures are above zero and are positively correlatedwith the confining pressure and the difference value under

adjacent confining pressure is up to 80 kPa In contrast thepore pressure of the coral mud first rises to a positive peak ina small range and then decreases to a stable negative valuee reason for the difference may be the mineral compo-sition Calcium carbonate is the main substance that makesup the coral mud whose coefficient of permeability is higherthan that of common clay erefore the pore pressure ofcoral mud is hard to accumulate

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

200

400

600

800

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(a)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(b)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

(c)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

600

1200

1800

2400

(σ1ndash

σ 3)

kPa

(d)

Figure 6 Stress-strain behaviour at different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Table 4 Coulomb-molar parameters of coral mud and Taizhou soil

Type c1 (kPa) c2 (kPa) c3 (kPa) c4 (kPa) c5 (kPa) c6 (kPa) c (kPa) φ1 φ2 φ3 φ4 φ5 φ6 φCoral mud 12265 12391 6885 16834 294 159 8138 23deg 21deg 33deg 18deg 37deg 46deg 279degTaizhou soil 6762 4616 5479 201 363 1503 5365 11deg 17deg 15deg 22deg 16deg 9deg 150deg

6 Advances in Civil Engineering

322 Effects of the Initial Void Ratio e pore pressureswith different e0 values are shown in Figure 9 e peak porepressure of both samples increases with increasing e0 butcoral mud has a larger difference value with respect to thepore pressure as e0 changes

e pore pressure coefficient of sample failure isexpressed as Af to represent the final failure state e re-lationships between Af and e0 are shown in Figure 10 It isclear that Af and e0 are linearly correlated but the effect of e0varies under different p0 values When p0 100 kPa e0 hasthe greatest effect and Af tends to be stable with increasingp0 demonstrating that the two factors are not independentof each other in terms of their effects on Af

33 Effective Stress Path In conventional triaxial tests theeffective stress path is usually expressed in the prsquo-q planewhere prsquo ismean effective stress and q is deviatoric stresses

pprime σ1 + 2σ3

3minus u

q

3+ σ1 minus u

q 12

radic

σ1prime minus σ2prime( 11138572

+ σ2prime minus σ3prime( 11138572

+ σ3prime minus σ1prime( 11138572

1113969 (1)

As shown in Figure 11 because of the unique porepressure developments during undrained shearing the ef-fective stress path of coral mud is unlike the normallyconsolidated clay curve which develops to the left [28] or the

01 1 10 100 10000

150

300

450

600

lgt (min)

u (k

Pa)

σ3 = 400kPaσ3 = 400kPaσ3 = 200kPaσ3 = 200kPa

Taizhou soilCoral mudTaizhou soilCoral mud

Figure 7 Pore pressure dissipation curve at the consolidation stage

u (k

Pa)

0

100

200

300

100kPa (Taizhou soil) 100kPa (coral mud)200kPa (Taizhou soil) 200kPa (coral mud)300kPa (Taizhou soil) 300kPa (coral mud)400kPa (Taizhou soil) 400kPa (coral mud)

0 2 4 6 8 10 12 14 16ndash2ε ()

Figure 8 Pore pressures under different confining pressures

Advances in Civil Engineering 7

general silt with an ldquoSrdquo curve [29] Additionally effectivestress path is also not the same as the curve of over-consolidated clay which obviously develops from right toleft [30]is path is similar to the total stress path curve anddevelops in a straight line Although the stress path curvesunder different confining pressures are always similar asconfining pressure does not change the critical state of thesoil mass compared with Taizhou soil the stress path ofcoral mud is less affected e surge of pore pressure onlyexists at e0 089 and p0 400 kPa in the early shear phasewhich causes a significant inflection point and the

inclination of other stress path curves of coral mud is almostequal

Drawing the critical state line (CSL) according to thestress path as shown in Figure 12 there is a good linearrelationship between qcs and pcsacute and it passes through theorigin which is consistent with the studies of other scholarsFigure 12 also shows the effective stress ratio Mcs at thecritical state It can be concluded that the Mcs value ofTaizhou soil declines with increasing e0 while that of coralmud first decreases and then slightly increases with in-creasing e0 corresponding to the testing results that when

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120u

(kPa

)

(a)

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120

160

200

u (k

Pa)

(b)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(c)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

300

350

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(d)

Figure 9 Pore pressures with different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

8 Advances in Civil Engineering

e0 089 the deviatoric stress of coral mud continues toincrease and finally is higher than the samples of e0 083

34 Friction Angle e mobilized friction angle φm underthe triaxial compression condition is defined as [31]

sinφm 3η

6 + η (2)

where η is defined as the ratio of the deviatoric stress q to theeffective mean stress prsquo

065 070 075 080 085 090

ndash008

ndash004

000

004

Af = 0268e0 ndash 0264 (simulation)Af = 0162e0 ndash 0153 (simulation)Af = 0162e0 ndash 0143 (simulation)Af = 0117e0 ndash 0097 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

(a)

Af = 1128e0 ndash 0692 (simulation)Af = 0977e0 ndash 0390 (simulation)Af = 0812e0 ndash 0258 (simulation)Af = 0883e0 ndash 0244 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

065 070 075 080 085 09000

01

02

03

04

05

06

07

08

(b)

Figure 10 Relationship between af and e0 (a) coral mud and (b) Taizhou soil

0 300 600 900pprime(kPa)

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

0

500

1000

1500

2000

2500

q (k

Pa)

(a)

pprime(kPa)

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

0 200 400 6000

300

600

900

q (k

Pa)

(b)

Figure 11 Effective stress paths with different initial void ratios (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 9

η q

pprime (3)

e critical state friction angle φcs under the triaxialcompression condition can be defined as

sinφcs 3ηcs

6 + ηcs (4)

where ηcs is critical state stress ratioe test data show that ηonly changes slightly when the strain is 15 According tothe critical state theory [32] the stress state under this straincould be considered a critical state

e peak state friction angle φps is defined as

sinφps 3ηps

6 + ηps (5)

where ηps is the peak state stress ratioFigure 13 presents the mobilized friction angle of coral

mud and Taizhou soil at different initial void ratios andpressures e values of φcs and φps are shown in Table 5Similar to the stress-strain relationship the mobilizedfriction angle-strain relationship of coral mud presents aplatform shape and when e0 089 the curve has theproperty of overpenetration while the other curves decreasewith an increase in the initial void ratio Most φps valuesoverlap with φcs and the remainder gradually approach thecritical state φcs of coral mud is much greater than that ofTaizhou soil and with increasing confining pressure φcs ofcoral mud tends to disperse while the Taizhou soil tends tobe dense indicating that the initial void ratio has a minoreffect on φcs of coral mud when the confining pressure is low

As shown in Figure 14 φcs of Taizhou soil decreases firstand then tends to be stable with an increase in the confiningpressure which indicates that an increase in the confining

pressure gradually has less influence on the critical frictionangle of Taizhou soil Figure 15(b) also proves this con-clusion as the 300 kPa and 400 kPa curves almost coincideIn contrast the confining pressure is an important pa-rameter on φcs of coral mud With an increase in theconfining pressure φcs first decreases and then increaseswhen e0 078 and e0 083 first increases then decreasesand then increases when e0 069 and first decreases thenincreases and then decreases when e0 089 Figure 15(a)illustrates that at 100 kPa the effect of the initial void ratio isminor as the curve approximates a straight line which isconsistent with the phenomenon of the high coincidence ofφcs in Figure 13(a) Under the other confining pressures φcsof coral mud first decreases and then increases with theincrease in e0p0 is the initial confining pressure e0 is theinitial void ratio φcs-c is the critical state friction angle ofcoral mud φps-c is the peak state friction angle of coral mudφcs-T is the critical state friction angle of Taizhou soil andφps-T is the peak state friction angle of Taizhou soil

35Modulus e initial elastic modulus E0i is an importantparameter indicating the deformation behaviour of coralmud It can be expressed as [33]

E0i qα

εα (6)

where εa means the axial strain constrained within 01 forthe initial slope of the stress-strain curve where the de-formation is supposed to be elastic

E50 is the ratio of the stress of half of the peak stress of soilto the corresponding strain [34] which is defined as

E50 05qps

εaps (7)

0 400 800 1200

e0 = 069e0 = 078e0 = 083e0 = 089

M = 1722M = 1675M = 1539M = 1655

pprime(kPa)

0

400

800

1200

1600

q (k

Pa)

(a)

e0 = 069e0 = 083e0 = 089

M = 1481M = 1426M = 1373

0 200 400pprime(kPa)

0

200

400

600

800

q (k

Pa)

(b)

Figure 12 Mcs with different initial void ratios (a) coral mud and (b) Taizhou soil

10 Advances in Civil Engineering

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

Figure 7 coral mud has a better permeability with a higherdissipation rate of the pore pressure Figure 8 presents thepore pressure at the shear stage For Taizhou soil the poresare similar to those of common clay that gradually develop toa peak after ε 2when the cement material is extruded andthe particles are in direct contact During the whole processthe pressures are above zero and are positively correlatedwith the confining pressure and the difference value under

adjacent confining pressure is up to 80 kPa In contrast thepore pressure of the coral mud first rises to a positive peak ina small range and then decreases to a stable negative valuee reason for the difference may be the mineral compo-sition Calcium carbonate is the main substance that makesup the coral mud whose coefficient of permeability is higherthan that of common clay erefore the pore pressure ofcoral mud is hard to accumulate

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

200

400

600

800

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(a)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

2 4 6 8 10 12 14 160ε ()

(b)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

400

800

1200

1600

(σ1ndash

σ 3)

kPa

(c)

e0 = 089 (Taizhou soil)

e0 = 069 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 089 (coral mud)

e0 = 069 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

2 4 6 8 10 12 14 160ε ()

0

600

1200

1800

2400

(σ1ndash

σ 3)

kPa

(d)

Figure 6 Stress-strain behaviour at different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Table 4 Coulomb-molar parameters of coral mud and Taizhou soil

Type c1 (kPa) c2 (kPa) c3 (kPa) c4 (kPa) c5 (kPa) c6 (kPa) c (kPa) φ1 φ2 φ3 φ4 φ5 φ6 φCoral mud 12265 12391 6885 16834 294 159 8138 23deg 21deg 33deg 18deg 37deg 46deg 279degTaizhou soil 6762 4616 5479 201 363 1503 5365 11deg 17deg 15deg 22deg 16deg 9deg 150deg

6 Advances in Civil Engineering

322 Effects of the Initial Void Ratio e pore pressureswith different e0 values are shown in Figure 9 e peak porepressure of both samples increases with increasing e0 butcoral mud has a larger difference value with respect to thepore pressure as e0 changes

e pore pressure coefficient of sample failure isexpressed as Af to represent the final failure state e re-lationships between Af and e0 are shown in Figure 10 It isclear that Af and e0 are linearly correlated but the effect of e0varies under different p0 values When p0 100 kPa e0 hasthe greatest effect and Af tends to be stable with increasingp0 demonstrating that the two factors are not independentof each other in terms of their effects on Af

33 Effective Stress Path In conventional triaxial tests theeffective stress path is usually expressed in the prsquo-q planewhere prsquo ismean effective stress and q is deviatoric stresses

pprime σ1 + 2σ3

3minus u

q

3+ σ1 minus u

q 12

radic

σ1prime minus σ2prime( 11138572

+ σ2prime minus σ3prime( 11138572

+ σ3prime minus σ1prime( 11138572

1113969 (1)

As shown in Figure 11 because of the unique porepressure developments during undrained shearing the ef-fective stress path of coral mud is unlike the normallyconsolidated clay curve which develops to the left [28] or the

01 1 10 100 10000

150

300

450

600

lgt (min)

u (k

Pa)

σ3 = 400kPaσ3 = 400kPaσ3 = 200kPaσ3 = 200kPa

Taizhou soilCoral mudTaizhou soilCoral mud

Figure 7 Pore pressure dissipation curve at the consolidation stage

u (k

Pa)

0

100

200

300

100kPa (Taizhou soil) 100kPa (coral mud)200kPa (Taizhou soil) 200kPa (coral mud)300kPa (Taizhou soil) 300kPa (coral mud)400kPa (Taizhou soil) 400kPa (coral mud)

0 2 4 6 8 10 12 14 16ndash2ε ()

Figure 8 Pore pressures under different confining pressures

Advances in Civil Engineering 7

general silt with an ldquoSrdquo curve [29] Additionally effectivestress path is also not the same as the curve of over-consolidated clay which obviously develops from right toleft [30]is path is similar to the total stress path curve anddevelops in a straight line Although the stress path curvesunder different confining pressures are always similar asconfining pressure does not change the critical state of thesoil mass compared with Taizhou soil the stress path ofcoral mud is less affected e surge of pore pressure onlyexists at e0 089 and p0 400 kPa in the early shear phasewhich causes a significant inflection point and the

inclination of other stress path curves of coral mud is almostequal

Drawing the critical state line (CSL) according to thestress path as shown in Figure 12 there is a good linearrelationship between qcs and pcsacute and it passes through theorigin which is consistent with the studies of other scholarsFigure 12 also shows the effective stress ratio Mcs at thecritical state It can be concluded that the Mcs value ofTaizhou soil declines with increasing e0 while that of coralmud first decreases and then slightly increases with in-creasing e0 corresponding to the testing results that when

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120u

(kPa

)

(a)

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120

160

200

u (k

Pa)

(b)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(c)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

300

350

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(d)

Figure 9 Pore pressures with different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

8 Advances in Civil Engineering

e0 089 the deviatoric stress of coral mud continues toincrease and finally is higher than the samples of e0 083

34 Friction Angle e mobilized friction angle φm underthe triaxial compression condition is defined as [31]

sinφm 3η

6 + η (2)

where η is defined as the ratio of the deviatoric stress q to theeffective mean stress prsquo

065 070 075 080 085 090

ndash008

ndash004

000

004

Af = 0268e0 ndash 0264 (simulation)Af = 0162e0 ndash 0153 (simulation)Af = 0162e0 ndash 0143 (simulation)Af = 0117e0 ndash 0097 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

(a)

Af = 1128e0 ndash 0692 (simulation)Af = 0977e0 ndash 0390 (simulation)Af = 0812e0 ndash 0258 (simulation)Af = 0883e0 ndash 0244 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

065 070 075 080 085 09000

01

02

03

04

05

06

07

08

(b)

Figure 10 Relationship between af and e0 (a) coral mud and (b) Taizhou soil

0 300 600 900pprime(kPa)

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

0

500

1000

1500

2000

2500

q (k

Pa)

(a)

pprime(kPa)

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

0 200 400 6000

300

600

900

q (k

Pa)

(b)

Figure 11 Effective stress paths with different initial void ratios (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 9

η q

pprime (3)

e critical state friction angle φcs under the triaxialcompression condition can be defined as

sinφcs 3ηcs

6 + ηcs (4)

where ηcs is critical state stress ratioe test data show that ηonly changes slightly when the strain is 15 According tothe critical state theory [32] the stress state under this straincould be considered a critical state

e peak state friction angle φps is defined as

sinφps 3ηps

6 + ηps (5)

where ηps is the peak state stress ratioFigure 13 presents the mobilized friction angle of coral

mud and Taizhou soil at different initial void ratios andpressures e values of φcs and φps are shown in Table 5Similar to the stress-strain relationship the mobilizedfriction angle-strain relationship of coral mud presents aplatform shape and when e0 089 the curve has theproperty of overpenetration while the other curves decreasewith an increase in the initial void ratio Most φps valuesoverlap with φcs and the remainder gradually approach thecritical state φcs of coral mud is much greater than that ofTaizhou soil and with increasing confining pressure φcs ofcoral mud tends to disperse while the Taizhou soil tends tobe dense indicating that the initial void ratio has a minoreffect on φcs of coral mud when the confining pressure is low

As shown in Figure 14 φcs of Taizhou soil decreases firstand then tends to be stable with an increase in the confiningpressure which indicates that an increase in the confining

pressure gradually has less influence on the critical frictionangle of Taizhou soil Figure 15(b) also proves this con-clusion as the 300 kPa and 400 kPa curves almost coincideIn contrast the confining pressure is an important pa-rameter on φcs of coral mud With an increase in theconfining pressure φcs first decreases and then increaseswhen e0 078 and e0 083 first increases then decreasesand then increases when e0 069 and first decreases thenincreases and then decreases when e0 089 Figure 15(a)illustrates that at 100 kPa the effect of the initial void ratio isminor as the curve approximates a straight line which isconsistent with the phenomenon of the high coincidence ofφcs in Figure 13(a) Under the other confining pressures φcsof coral mud first decreases and then increases with theincrease in e0p0 is the initial confining pressure e0 is theinitial void ratio φcs-c is the critical state friction angle ofcoral mud φps-c is the peak state friction angle of coral mudφcs-T is the critical state friction angle of Taizhou soil andφps-T is the peak state friction angle of Taizhou soil

35Modulus e initial elastic modulus E0i is an importantparameter indicating the deformation behaviour of coralmud It can be expressed as [33]

E0i qα

εα (6)

where εa means the axial strain constrained within 01 forthe initial slope of the stress-strain curve where the de-formation is supposed to be elastic

E50 is the ratio of the stress of half of the peak stress of soilto the corresponding strain [34] which is defined as

E50 05qps

εaps (7)

0 400 800 1200

e0 = 069e0 = 078e0 = 083e0 = 089

M = 1722M = 1675M = 1539M = 1655

pprime(kPa)

0

400

800

1200

1600

q (k

Pa)

(a)

e0 = 069e0 = 083e0 = 089

M = 1481M = 1426M = 1373

0 200 400pprime(kPa)

0

200

400

600

800

q (k

Pa)

(b)

Figure 12 Mcs with different initial void ratios (a) coral mud and (b) Taizhou soil

10 Advances in Civil Engineering

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

322 Effects of the Initial Void Ratio e pore pressureswith different e0 values are shown in Figure 9 e peak porepressure of both samples increases with increasing e0 butcoral mud has a larger difference value with respect to thepore pressure as e0 changes

e pore pressure coefficient of sample failure isexpressed as Af to represent the final failure state e re-lationships between Af and e0 are shown in Figure 10 It isclear that Af and e0 are linearly correlated but the effect of e0varies under different p0 values When p0 100 kPa e0 hasthe greatest effect and Af tends to be stable with increasingp0 demonstrating that the two factors are not independentof each other in terms of their effects on Af

33 Effective Stress Path In conventional triaxial tests theeffective stress path is usually expressed in the prsquo-q planewhere prsquo ismean effective stress and q is deviatoric stresses

pprime σ1 + 2σ3

3minus u

q

3+ σ1 minus u

q 12

radic

σ1prime minus σ2prime( 11138572

+ σ2prime minus σ3prime( 11138572

+ σ3prime minus σ1prime( 11138572

1113969 (1)

As shown in Figure 11 because of the unique porepressure developments during undrained shearing the ef-fective stress path of coral mud is unlike the normallyconsolidated clay curve which develops to the left [28] or the

01 1 10 100 10000

150

300

450

600

lgt (min)

u (k

Pa)

σ3 = 400kPaσ3 = 400kPaσ3 = 200kPaσ3 = 200kPa

Taizhou soilCoral mudTaizhou soilCoral mud

Figure 7 Pore pressure dissipation curve at the consolidation stage

u (k

Pa)

0

100

200

300

100kPa (Taizhou soil) 100kPa (coral mud)200kPa (Taizhou soil) 200kPa (coral mud)300kPa (Taizhou soil) 300kPa (coral mud)400kPa (Taizhou soil) 400kPa (coral mud)

0 2 4 6 8 10 12 14 16ndash2ε ()

Figure 8 Pore pressures under different confining pressures

Advances in Civil Engineering 7

general silt with an ldquoSrdquo curve [29] Additionally effectivestress path is also not the same as the curve of over-consolidated clay which obviously develops from right toleft [30]is path is similar to the total stress path curve anddevelops in a straight line Although the stress path curvesunder different confining pressures are always similar asconfining pressure does not change the critical state of thesoil mass compared with Taizhou soil the stress path ofcoral mud is less affected e surge of pore pressure onlyexists at e0 089 and p0 400 kPa in the early shear phasewhich causes a significant inflection point and the

inclination of other stress path curves of coral mud is almostequal

Drawing the critical state line (CSL) according to thestress path as shown in Figure 12 there is a good linearrelationship between qcs and pcsacute and it passes through theorigin which is consistent with the studies of other scholarsFigure 12 also shows the effective stress ratio Mcs at thecritical state It can be concluded that the Mcs value ofTaizhou soil declines with increasing e0 while that of coralmud first decreases and then slightly increases with in-creasing e0 corresponding to the testing results that when

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120u

(kPa

)

(a)

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120

160

200

u (k

Pa)

(b)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(c)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

300

350

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(d)

Figure 9 Pore pressures with different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

8 Advances in Civil Engineering

e0 089 the deviatoric stress of coral mud continues toincrease and finally is higher than the samples of e0 083

34 Friction Angle e mobilized friction angle φm underthe triaxial compression condition is defined as [31]

sinφm 3η

6 + η (2)

where η is defined as the ratio of the deviatoric stress q to theeffective mean stress prsquo

065 070 075 080 085 090

ndash008

ndash004

000

004

Af = 0268e0 ndash 0264 (simulation)Af = 0162e0 ndash 0153 (simulation)Af = 0162e0 ndash 0143 (simulation)Af = 0117e0 ndash 0097 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

(a)

Af = 1128e0 ndash 0692 (simulation)Af = 0977e0 ndash 0390 (simulation)Af = 0812e0 ndash 0258 (simulation)Af = 0883e0 ndash 0244 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

065 070 075 080 085 09000

01

02

03

04

05

06

07

08

(b)

Figure 10 Relationship between af and e0 (a) coral mud and (b) Taizhou soil

0 300 600 900pprime(kPa)

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

0

500

1000

1500

2000

2500

q (k

Pa)

(a)

pprime(kPa)

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

0 200 400 6000

300

600

900

q (k

Pa)

(b)

Figure 11 Effective stress paths with different initial void ratios (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 9

η q

pprime (3)

e critical state friction angle φcs under the triaxialcompression condition can be defined as

sinφcs 3ηcs

6 + ηcs (4)

where ηcs is critical state stress ratioe test data show that ηonly changes slightly when the strain is 15 According tothe critical state theory [32] the stress state under this straincould be considered a critical state

e peak state friction angle φps is defined as

sinφps 3ηps

6 + ηps (5)

where ηps is the peak state stress ratioFigure 13 presents the mobilized friction angle of coral

mud and Taizhou soil at different initial void ratios andpressures e values of φcs and φps are shown in Table 5Similar to the stress-strain relationship the mobilizedfriction angle-strain relationship of coral mud presents aplatform shape and when e0 089 the curve has theproperty of overpenetration while the other curves decreasewith an increase in the initial void ratio Most φps valuesoverlap with φcs and the remainder gradually approach thecritical state φcs of coral mud is much greater than that ofTaizhou soil and with increasing confining pressure φcs ofcoral mud tends to disperse while the Taizhou soil tends tobe dense indicating that the initial void ratio has a minoreffect on φcs of coral mud when the confining pressure is low

As shown in Figure 14 φcs of Taizhou soil decreases firstand then tends to be stable with an increase in the confiningpressure which indicates that an increase in the confining

pressure gradually has less influence on the critical frictionangle of Taizhou soil Figure 15(b) also proves this con-clusion as the 300 kPa and 400 kPa curves almost coincideIn contrast the confining pressure is an important pa-rameter on φcs of coral mud With an increase in theconfining pressure φcs first decreases and then increaseswhen e0 078 and e0 083 first increases then decreasesand then increases when e0 069 and first decreases thenincreases and then decreases when e0 089 Figure 15(a)illustrates that at 100 kPa the effect of the initial void ratio isminor as the curve approximates a straight line which isconsistent with the phenomenon of the high coincidence ofφcs in Figure 13(a) Under the other confining pressures φcsof coral mud first decreases and then increases with theincrease in e0p0 is the initial confining pressure e0 is theinitial void ratio φcs-c is the critical state friction angle ofcoral mud φps-c is the peak state friction angle of coral mudφcs-T is the critical state friction angle of Taizhou soil andφps-T is the peak state friction angle of Taizhou soil

35Modulus e initial elastic modulus E0i is an importantparameter indicating the deformation behaviour of coralmud It can be expressed as [33]

E0i qα

εα (6)

where εa means the axial strain constrained within 01 forthe initial slope of the stress-strain curve where the de-formation is supposed to be elastic

E50 is the ratio of the stress of half of the peak stress of soilto the corresponding strain [34] which is defined as

E50 05qps

εaps (7)

0 400 800 1200

e0 = 069e0 = 078e0 = 083e0 = 089

M = 1722M = 1675M = 1539M = 1655

pprime(kPa)

0

400

800

1200

1600

q (k

Pa)

(a)

e0 = 069e0 = 083e0 = 089

M = 1481M = 1426M = 1373

0 200 400pprime(kPa)

0

200

400

600

800

q (k

Pa)

(b)

Figure 12 Mcs with different initial void ratios (a) coral mud and (b) Taizhou soil

10 Advances in Civil Engineering

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

general silt with an ldquoSrdquo curve [29] Additionally effectivestress path is also not the same as the curve of over-consolidated clay which obviously develops from right toleft [30]is path is similar to the total stress path curve anddevelops in a straight line Although the stress path curvesunder different confining pressures are always similar asconfining pressure does not change the critical state of thesoil mass compared with Taizhou soil the stress path ofcoral mud is less affected e surge of pore pressure onlyexists at e0 089 and p0 400 kPa in the early shear phasewhich causes a significant inflection point and the

inclination of other stress path curves of coral mud is almostequal

Drawing the critical state line (CSL) according to thestress path as shown in Figure 12 there is a good linearrelationship between qcs and pcsacute and it passes through theorigin which is consistent with the studies of other scholarsFigure 12 also shows the effective stress ratio Mcs at thecritical state It can be concluded that the Mcs value ofTaizhou soil declines with increasing e0 while that of coralmud first decreases and then slightly increases with in-creasing e0 corresponding to the testing results that when

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120u

(kPa

)

(a)

0 2 4 6 8 10 12 14 16ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

ndash40

0

40

80

120

160

200

u (k

Pa)

(b)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(c)

0 2 4 6 8 10 12 14 16ndash50

0

50

100

150

200

250

300

350

ε ()

e0 = 069 (Taizhou soil)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)

e0 = 069 (coral mud)

e0 = 089 (coral mud)e0 = 078 (coral mud)

e0 = 083 (coral mud)

u (k

Pa)

(d)

Figure 9 Pore pressures with different initial void ratios (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

8 Advances in Civil Engineering

e0 089 the deviatoric stress of coral mud continues toincrease and finally is higher than the samples of e0 083

34 Friction Angle e mobilized friction angle φm underthe triaxial compression condition is defined as [31]

sinφm 3η

6 + η (2)

where η is defined as the ratio of the deviatoric stress q to theeffective mean stress prsquo

065 070 075 080 085 090

ndash008

ndash004

000

004

Af = 0268e0 ndash 0264 (simulation)Af = 0162e0 ndash 0153 (simulation)Af = 0162e0 ndash 0143 (simulation)Af = 0117e0 ndash 0097 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

(a)

Af = 1128e0 ndash 0692 (simulation)Af = 0977e0 ndash 0390 (simulation)Af = 0812e0 ndash 0258 (simulation)Af = 0883e0 ndash 0244 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

065 070 075 080 085 09000

01

02

03

04

05

06

07

08

(b)

Figure 10 Relationship between af and e0 (a) coral mud and (b) Taizhou soil

0 300 600 900pprime(kPa)

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

0

500

1000

1500

2000

2500

q (k

Pa)

(a)

pprime(kPa)

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

0 200 400 6000

300

600

900

q (k

Pa)

(b)

Figure 11 Effective stress paths with different initial void ratios (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 9

η q

pprime (3)

e critical state friction angle φcs under the triaxialcompression condition can be defined as

sinφcs 3ηcs

6 + ηcs (4)

where ηcs is critical state stress ratioe test data show that ηonly changes slightly when the strain is 15 According tothe critical state theory [32] the stress state under this straincould be considered a critical state

e peak state friction angle φps is defined as

sinφps 3ηps

6 + ηps (5)

where ηps is the peak state stress ratioFigure 13 presents the mobilized friction angle of coral

mud and Taizhou soil at different initial void ratios andpressures e values of φcs and φps are shown in Table 5Similar to the stress-strain relationship the mobilizedfriction angle-strain relationship of coral mud presents aplatform shape and when e0 089 the curve has theproperty of overpenetration while the other curves decreasewith an increase in the initial void ratio Most φps valuesoverlap with φcs and the remainder gradually approach thecritical state φcs of coral mud is much greater than that ofTaizhou soil and with increasing confining pressure φcs ofcoral mud tends to disperse while the Taizhou soil tends tobe dense indicating that the initial void ratio has a minoreffect on φcs of coral mud when the confining pressure is low

As shown in Figure 14 φcs of Taizhou soil decreases firstand then tends to be stable with an increase in the confiningpressure which indicates that an increase in the confining

pressure gradually has less influence on the critical frictionangle of Taizhou soil Figure 15(b) also proves this con-clusion as the 300 kPa and 400 kPa curves almost coincideIn contrast the confining pressure is an important pa-rameter on φcs of coral mud With an increase in theconfining pressure φcs first decreases and then increaseswhen e0 078 and e0 083 first increases then decreasesand then increases when e0 069 and first decreases thenincreases and then decreases when e0 089 Figure 15(a)illustrates that at 100 kPa the effect of the initial void ratio isminor as the curve approximates a straight line which isconsistent with the phenomenon of the high coincidence ofφcs in Figure 13(a) Under the other confining pressures φcsof coral mud first decreases and then increases with theincrease in e0p0 is the initial confining pressure e0 is theinitial void ratio φcs-c is the critical state friction angle ofcoral mud φps-c is the peak state friction angle of coral mudφcs-T is the critical state friction angle of Taizhou soil andφps-T is the peak state friction angle of Taizhou soil

35Modulus e initial elastic modulus E0i is an importantparameter indicating the deformation behaviour of coralmud It can be expressed as [33]

E0i qα

εα (6)

where εa means the axial strain constrained within 01 forthe initial slope of the stress-strain curve where the de-formation is supposed to be elastic

E50 is the ratio of the stress of half of the peak stress of soilto the corresponding strain [34] which is defined as

E50 05qps

εaps (7)

0 400 800 1200

e0 = 069e0 = 078e0 = 083e0 = 089

M = 1722M = 1675M = 1539M = 1655

pprime(kPa)

0

400

800

1200

1600

q (k

Pa)

(a)

e0 = 069e0 = 083e0 = 089

M = 1481M = 1426M = 1373

0 200 400pprime(kPa)

0

200

400

600

800

q (k

Pa)

(b)

Figure 12 Mcs with different initial void ratios (a) coral mud and (b) Taizhou soil

10 Advances in Civil Engineering

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

e0 089 the deviatoric stress of coral mud continues toincrease and finally is higher than the samples of e0 083

34 Friction Angle e mobilized friction angle φm underthe triaxial compression condition is defined as [31]

sinφm 3η

6 + η (2)

where η is defined as the ratio of the deviatoric stress q to theeffective mean stress prsquo

065 070 075 080 085 090

ndash008

ndash004

000

004

Af = 0268e0 ndash 0264 (simulation)Af = 0162e0 ndash 0153 (simulation)Af = 0162e0 ndash 0143 (simulation)Af = 0117e0 ndash 0097 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

(a)

Af = 1128e0 ndash 0692 (simulation)Af = 0977e0 ndash 0390 (simulation)Af = 0812e0 ndash 0258 (simulation)Af = 0883e0 ndash 0244 (simulation)

100kPa (test data)200kPa (test data)300kPa (test data)400kPa (test data)

A f

e0

065 070 075 080 085 09000

01

02

03

04

05

06

07

08

(b)

Figure 10 Relationship between af and e0 (a) coral mud and (b) Taizhou soil

0 300 600 900pprime(kPa)

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

e0 = 069e0 = 078e0 = 083e0 = 089

0

500

1000

1500

2000

2500

q (k

Pa)

(a)

pprime(kPa)

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

e0 = 069e0 = 083e0 = 089

0 200 400 6000

300

600

900

q (k

Pa)

(b)

Figure 11 Effective stress paths with different initial void ratios (a) coral mud and (b) Taizhou soil

Advances in Civil Engineering 9

η q

pprime (3)

e critical state friction angle φcs under the triaxialcompression condition can be defined as

sinφcs 3ηcs

6 + ηcs (4)

where ηcs is critical state stress ratioe test data show that ηonly changes slightly when the strain is 15 According tothe critical state theory [32] the stress state under this straincould be considered a critical state

e peak state friction angle φps is defined as

sinφps 3ηps

6 + ηps (5)

where ηps is the peak state stress ratioFigure 13 presents the mobilized friction angle of coral

mud and Taizhou soil at different initial void ratios andpressures e values of φcs and φps are shown in Table 5Similar to the stress-strain relationship the mobilizedfriction angle-strain relationship of coral mud presents aplatform shape and when e0 089 the curve has theproperty of overpenetration while the other curves decreasewith an increase in the initial void ratio Most φps valuesoverlap with φcs and the remainder gradually approach thecritical state φcs of coral mud is much greater than that ofTaizhou soil and with increasing confining pressure φcs ofcoral mud tends to disperse while the Taizhou soil tends tobe dense indicating that the initial void ratio has a minoreffect on φcs of coral mud when the confining pressure is low

As shown in Figure 14 φcs of Taizhou soil decreases firstand then tends to be stable with an increase in the confiningpressure which indicates that an increase in the confining

pressure gradually has less influence on the critical frictionangle of Taizhou soil Figure 15(b) also proves this con-clusion as the 300 kPa and 400 kPa curves almost coincideIn contrast the confining pressure is an important pa-rameter on φcs of coral mud With an increase in theconfining pressure φcs first decreases and then increaseswhen e0 078 and e0 083 first increases then decreasesand then increases when e0 069 and first decreases thenincreases and then decreases when e0 089 Figure 15(a)illustrates that at 100 kPa the effect of the initial void ratio isminor as the curve approximates a straight line which isconsistent with the phenomenon of the high coincidence ofφcs in Figure 13(a) Under the other confining pressures φcsof coral mud first decreases and then increases with theincrease in e0p0 is the initial confining pressure e0 is theinitial void ratio φcs-c is the critical state friction angle ofcoral mud φps-c is the peak state friction angle of coral mudφcs-T is the critical state friction angle of Taizhou soil andφps-T is the peak state friction angle of Taizhou soil

35Modulus e initial elastic modulus E0i is an importantparameter indicating the deformation behaviour of coralmud It can be expressed as [33]

E0i qα

εα (6)

where εa means the axial strain constrained within 01 forthe initial slope of the stress-strain curve where the de-formation is supposed to be elastic

E50 is the ratio of the stress of half of the peak stress of soilto the corresponding strain [34] which is defined as

E50 05qps

εaps (7)

0 400 800 1200

e0 = 069e0 = 078e0 = 083e0 = 089

M = 1722M = 1675M = 1539M = 1655

pprime(kPa)

0

400

800

1200

1600

q (k

Pa)

(a)

e0 = 069e0 = 083e0 = 089

M = 1481M = 1426M = 1373

0 200 400pprime(kPa)

0

200

400

600

800

q (k

Pa)

(b)

Figure 12 Mcs with different initial void ratios (a) coral mud and (b) Taizhou soil

10 Advances in Civil Engineering

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

η q

pprime (3)

e critical state friction angle φcs under the triaxialcompression condition can be defined as

sinφcs 3ηcs

6 + ηcs (4)

where ηcs is critical state stress ratioe test data show that ηonly changes slightly when the strain is 15 According tothe critical state theory [32] the stress state under this straincould be considered a critical state

e peak state friction angle φps is defined as

sinφps 3ηps

6 + ηps (5)

where ηps is the peak state stress ratioFigure 13 presents the mobilized friction angle of coral

mud and Taizhou soil at different initial void ratios andpressures e values of φcs and φps are shown in Table 5Similar to the stress-strain relationship the mobilizedfriction angle-strain relationship of coral mud presents aplatform shape and when e0 089 the curve has theproperty of overpenetration while the other curves decreasewith an increase in the initial void ratio Most φps valuesoverlap with φcs and the remainder gradually approach thecritical state φcs of coral mud is much greater than that ofTaizhou soil and with increasing confining pressure φcs ofcoral mud tends to disperse while the Taizhou soil tends tobe dense indicating that the initial void ratio has a minoreffect on φcs of coral mud when the confining pressure is low

As shown in Figure 14 φcs of Taizhou soil decreases firstand then tends to be stable with an increase in the confiningpressure which indicates that an increase in the confining

pressure gradually has less influence on the critical frictionangle of Taizhou soil Figure 15(b) also proves this con-clusion as the 300 kPa and 400 kPa curves almost coincideIn contrast the confining pressure is an important pa-rameter on φcs of coral mud With an increase in theconfining pressure φcs first decreases and then increaseswhen e0 078 and e0 083 first increases then decreasesand then increases when e0 069 and first decreases thenincreases and then decreases when e0 089 Figure 15(a)illustrates that at 100 kPa the effect of the initial void ratio isminor as the curve approximates a straight line which isconsistent with the phenomenon of the high coincidence ofφcs in Figure 13(a) Under the other confining pressures φcsof coral mud first decreases and then increases with theincrease in e0p0 is the initial confining pressure e0 is theinitial void ratio φcs-c is the critical state friction angle ofcoral mud φps-c is the peak state friction angle of coral mudφcs-T is the critical state friction angle of Taizhou soil andφps-T is the peak state friction angle of Taizhou soil

35Modulus e initial elastic modulus E0i is an importantparameter indicating the deformation behaviour of coralmud It can be expressed as [33]

E0i qα

εα (6)

where εa means the axial strain constrained within 01 forthe initial slope of the stress-strain curve where the de-formation is supposed to be elastic

E50 is the ratio of the stress of half of the peak stress of soilto the corresponding strain [34] which is defined as

E50 05qps

εaps (7)

0 400 800 1200

e0 = 069e0 = 078e0 = 083e0 = 089

M = 1722M = 1675M = 1539M = 1655

pprime(kPa)

0

400

800

1200

1600

q (k

Pa)

(a)

e0 = 069e0 = 083e0 = 089

M = 1481M = 1426M = 1373

0 200 400pprime(kPa)

0

200

400

600

800

q (k

Pa)

(b)

Figure 12 Mcs with different initial void ratios (a) coral mud and (b) Taizhou soil

10 Advances in Civil Engineering

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

where qps is peak stress during shearing and εaps is the cor-responding strain Table 6 presents the values of E0i and E50and the relationships between E0i and E50 and p0 and e0 areshown in Figures 16 and 17 respectively

e initial elastic modulus of coral mud is nearly 10times that of Taizhou soil and the influences of p0 and e0 oncoral mud are more obvious and regular E0i of coral mudcan be expressed as a linear function of the logarithm of p0(R2˃098) while the slope of the fitted line equation does notchange with the change in e0 this result means that E0iincreases 13955MPa for every 100 kPa increase in lgp0

independent of e0 With an increase in e0 E0i of coral mudfirst decreases and then increases but the growth range issmall and the whole tends to be stable e relationshipbetween E0i and e0 under different confining pressures issimilar which also proves that the two factors are inde-pendent of each other

Similar to the initial elastic modulus the secant modulusof coral mud is also much higher than that of Taizhou soilE50 increases linearly with increasing lgp0 but the effects ofp0 and e0 on E50 of coral mud are not completely inde-pendent As shown in Figure 18 when e0 089 the slope of

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

(a)φ m

(deg)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(b)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(c)

φ m (deg

)

e0 = 089 (coral mud) e0 = 083 (coral mud) e0 = 083 (coral mud)

e0 = 089 (Taizhou soil)e0 = 083 (Taizhou soil)e0 = 069 (Taizhou soil)

e0 = 078 (coral mud) φpsφcs

ndash2 0 2 4 6 8 10 12 14 160

15

30

45

60

ε ()

(d)

Figure 13 Mobilized friction angle of coral mud and Taizhou soil (a) 100 kPa (b) 200 kPa (c) 300 kPa and (d) 400 kPa

Advances in Civil Engineering 11

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

the equation of the fitting line is much smaller than theothers due to its special hardening law Its stress increasescontinuously with the strain the strain corresponding to 05qps is larger and the secant modulus decreases accordinglyis characteristic is also shown in Figure 19 with the in-crease in e0 under different confining pressures E50 curvetends to be concentrated from parallel

36 Finite Element Simulation of the Stress-StrainRelationship e Cam-Clay model is suitable for predictingthe properties of normally consolidated and weakly over-consolidated clay under critical conditions [35] but whether it issuitable for coral mud remains to be studied e model pa-rameters λ κ and M obtained from one-dimensional

compression tests and CU shear tests under confining pressuresof 100 kPandash400kPa were used to simulate the tests under200kPa 400kPa and 600kPa according to the Cam-Claymodel

361 Calculation of the Cam-Clay Model ParametersFigure 20 shows the one-dimensional compression trialcurve of coral mud e curve is much gentler than thegeneral compression curve and the rebounding curve andunloading curve are close to coinciding indicating thatthe compressibility and resilience of coral mud are verylow

e relationship among λ κ M and e0 was plottedaccording to the compression index (Table 7) As shown in

Table 5 Critical state friction angle and peak state friction angle of coral mud and Taizhou soil

p0 (kPa) e0 φcs-c (deg) φps-c (deg) φcs-T (deg) φps-T (deg)

100

069 4216 4326 4532 4549078 4294 4294 mdash mdash083 4239 4239 4467 4467089 4309 4309 4175 4190

200

069 4341 4387 3860 3860078 4042 4042 mdash mdash083 3696 3847 3494 3494089 4009 4009 3340 3340

300

069 3849 3884 3490 3490078 3708 3708 mdash mdash083 3289 3347 3409 3409089 4095 4095 3310 3310

400

069 4148 4206 3535 3535078 4088 4088 mdash mdash083 3734 3734 3416 3416089 4027 4027 3321 3321

100 200 300 400p0 (kPa)

e0 = 069e0 = 078

e0 = 083e0 = 089

25

30

35

40

45

50

55

φ cs (

deg)

(a)

p0 (kPa)100 200 300 400

25

30

35

40

45

50

55φ c

s (deg)

e0 = 069e0 = 083e0 = 089

(b)

Figure 14 Relationship between φcs and p0 (a) coral mud and (b) Taizhou soil

12 Advances in Civil Engineering

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

Figure 21 λ is determined incrementally by a larger initialvoid ratio and κ fluctuates by approximately 00035 whileMfirst decreases then stabilizes and slightly risesese trendsare different from those of Taizhou soil in which M linearlydecreases with increasing e0

362 Simulation Results Analysis According to the labo-ratory test results the saturated coral mud sample with

e0 089 was subjected to a CU shear test simulation esample parameters were set as follows diameter 391mmheight 80mm confining pressures 200 kPa 400 kPa and600 kPa v 038 λ 0065 κ 0003 M 1655 e0 089and soil permeability coefficient 113times10minus6 cms

Figure 22 presents the relationship between the test resultsand the simulation Particularly the predicted modulus in theearly stage is smaller than the measured value and the model

07 08 0925

30

35

40

45

50

55φ c

s (deg)

e0

100kPa200kPa

300kPa400kPa

(a)

φ cs (

deg)

e0

100kPa200kPa

300kPa400kPa

07 08 0925

30

35

40

45

50

55

(b)

Figure 15 Relationship between φcs and e0 (a) coral mud and (b) Taizhou soil

Table 6 Initial elastic modulus and secant modulus at 50 of thepeak strength of moral mud and Taizhou soil

p0 (kPa) e0E0i-c(MPa)

E50-c(MPa)

E0i-T(MPa)

E50-T(MPa)

100

069 24167 8571 2500 3347078 15833 5674 mdash mdash083 6667 3287 1185 2381089 10371 5225 1667 2083

200

069 35033 13566 3333 983078 27544 9167 mdash mdash083 16667 8602 2667 526089 19445 8333 2778 585

300

069 40038 15802 4167 1032078 33805 12103 mdash mdash083 22512 9690 4167 673089 25013 7489 3788 611

400

069 44167 18561 4167 1221078 36126 14040 mdash mdash083 35571 11303 4445 721089 27517 7549 3788 634

p0 is the initial confining pressure e0 is the initial void ratio E0i-c is the initialelastic modulus of coral mud E50-c is the secant modulus of coral mud E0i-Tis the initial elastic modulus of Taizhou soil and E50-T is the secant modulusof Taizhou soil

100 1000

0

150

300

450

600

E0i = 13955palg(p0pa)ndash39501E0i = 13955palg(p0pa)ndash47031E0i = 13955palg(p0pa)ndash54766E0i = 13955palg(p0pa)ndash57498

e0 = 069e0 = 083e0 = 089e0 = 078

E 0i (

MPa

)

lgp0 (kPa)

Figure 16 Relationship between E0i and p0

Advances in Civil Engineering 13

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

could not well reflect the hardening characteristics in the laterstage e unique microstructure of coral mud may be thereason why simulated results do not match the experimentaldata at low strain range e irregular particles of coral mudcome into direct contact from the beginning and stress in-creases rapidly at the initial stage of shear different fromcommon clay whose stress gradually increases at a slower rateHowever the error between the predicted peak and the

measured value is small indicating that the Cam-Clay modelhas a certain reference for the stress-strain development ofcoral mud

4 ConclusionsIn this paper SEM was implemented to better understandthe microstructure of coral mud in the South China Sea Aseries of triaxial tests were conducted to study the static shearstrength behaviour Cam-Clay was employed to simulate thestress-strain behaviour of the coralmud to verify the estimationability e main conclusions can be summarized as follows

(1) e morphology of coral mud particles was ex-tremely irregular mainly strip and needle shapede strength of coral mud under the same confining

E 0i (

MPa

)

07 08 09

0

150

300

450

600

e0

100 kPa200 kPa300 kPa400 kPa

Figure 17 Relationship between E0i and e0

lgp0 (kPa)100 1000

ndash100

0

100

200

300

E50 = 1613palg(p0pa)ndash1560 (simulation)E50 = 6245palg(p0pa)ndash25501 (simulation)E50 = 6245palg(p0pa)ndash23475 (simulation)E50 = 6245palg(p0pa)ndash19596 (simulation)

e0 = 069e0 = 083

e0 = 089e0 = 078

E 50 (

MPa

)

Figure 18 Relationship between E50 and lgp0

e0

E 50 (

MPa

)

07 08 09ndash100

0

100

200

300

100 kPa (coral mud)200 kPa (coral mud)300 kPa (coral mud)400 kPa (coral mud)

100 kPa (Taizhou soil)200 kPa (Taizhou soil)300 kPa (Taizhou soil)400 kPa (Taizhou soil)

Figure 19 Relationship between E50 and e0

1 10 100 100005

06

07

08

09

e

lgp (kPa)

e0 = 078e0 = 069

e0 = 089e0 = 083

Figure 20 One-dimensional compression trial curve

14 Advances in Civil Engineering

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

pressure was much higher than that of Taizhou soile initial void ratio e0 and the initial confining pressurep0 affected the strength and deformation characteristicsWhen e0 089 the stress-strain plot exhibited an en-hanced curve regardless of the confining pressure

(2) e dissipation rate of the pore pressure in theconsolidation and shear stages of coral mud wasmuch higher than that of Taizhou soil and the di-latancy characteristic was significant When the

Table 7 Compression index of coral mud

Initial void ratio e0 Compression exponent cc Swelling index Cs λ κ069 01082 00086 00470 00037078 01156 00090 00502 00039083 01211 00078 00526 00034089 01505 00077 00654 00033

0045

0050

0055

0060

0065

Equationλ = 0639e0

2 ndash 0923e0 + 0526

Test dataSimulations

λ

070 075 080 085 090065e0

(a)

07 08 090000

0002

0004

0006

0008

κ

e0

(b)

EquationM = 4766e0

2 ndash 8053e0 + 5017

07 08 0910

12

14M

16

18

20

Coral mud (test data)Coral mud (simulations)Taizhou soil (test data)Taizhou soil (simulations)

e0

(c)

Figure 21 Relationship between the Cam-Clay model parameters and e0 (a) Relationship between λ and e0 of coral mud (b) Relationshipbetween κ and e0 of coral mud (c) Relationship between M and e0

0 2 4 6 8 10 12 14 16ε ()

σ3 = 200kPa (test data)σ3 = 400kPa (test data)σ3 = 600kPa (test data)

σ3 = 400kPa (simulation)σ3 = 600kPa (simulation)

σ3 = 200kPa (simulation)

0

500

1000

1500

2000

2500

3000

(σ1 ndash

σ3)

kPa

Figure 22 Relationship between the test results and simulation

Advances in Civil Engineering 15

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

failure occurred the pore pressure coefficient variedlinearly with the initial void ratio

(3) e effective stress path of coral mud was similar tothe total stress path due to the unique pore pressuredevelopment

(4) e peak friction angle of coral mud mostly coin-cided with the critical friction angle e initialconfining pressure had an important influence onthe critical friction angle of coral mud With theexception of 100 kPa the critical friction angle ofcoral mud first declined and then developed with anincrease in the initial void ratio

(5) e initial elastic modulus of coral mud was nearly10 times that of Taizhou soilis result showed thatthere was a linear relationship between the initialelastic modulus E0i and lgp0 as well as between thesecant modulus E50 and p0 e effects of p0 and e0on the E0i of coral mud were independent of eachother

(6) e value of parameter λ was determined incre-mentally by a larger initial void ratio while thevalue of parameterM decreased smoothly first andthen rose slightly the selection of parameter κ wasapproximately 00035 e results suggest that theCam-Clay model has a certain reference forpredicting the stress-strain relationship of coralmud

Notations

Cc Coefficient of curvatureCu Coefficient of uniformityR RoundnessT Aspect ratiop0 Initial confining pressureρd Dry densitye0 Initial void ratioc Coulomb-molar parameterφ Internal friction angleA Pore pressure coefficientprsquo Mean effective stressq Deviatoric stressprsquocs Mean effective stress at the critical stateqcs Deviatoric stress at the critical stateMcs Effective stress ratio at critical stateφcs Critical state peak stateφps Peak state peak stateηps Peak state stress ratioE0i Initial elastic modulusE50 Secant modulus at 50 of the peak strengthCs Swelling indexλ Compression indexκ Recompression index

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to acknowledge the financial supportof the National Natural Science Foundation of China underGrant 51979087

References

[1] H Zhao C Song Y Zhu et al Environmental and ResourceCharacteristics and Development of Nansha Islands Earth-quake Press Beijing China 1993

[2] X Wang ldquoStudy on the permeability characteristics of cal-careous silty intercalation in the foundation of artificial is-landrdquo Rock and Soil Mechanics vol 38 no 11 pp 3127ndash31352017

[3] Q Jin Geology and Oil and Gas Resources in the South ChinaSea Geology Press Beijing China 1989

[4] YWu H Yamamoto J Cui andH Cheng ldquoInfluence of loadmode on particle crushing characteristics of silica sand at highstressesrdquo International Journal of Geomechanics-ASCEvol 20 no 3 Article ID 04019194 2020

[5] J Li ldquoShear resistance of coral debris calcareous sandrdquoGeotechnical basis vol 31 no 2 pp 226ndash230 2017

[6] Z Sun and D Huang ldquoStudy on engineering properties ofcoral sand in Nansha Islandsrdquo Journal of Engineering geologypp 208ndash212 2000

[7] W Qian ldquoTriaxial tests of calcareous sand on Mohr-coulombstrength characteristicsrdquo Geotechnical foundation vol 31no 2 pp 321-322 2017

[8] R WangC Song et al Engineering Geology of Coral Reefs inNansha Islands Science Press Beijing China 1997

[9] J Zhang ldquoExperimental study on calcareous sand particlecrushing under shear actionrdquo Rock and Soil mechanicsvol 29 no 10 pp 2789ndash2793 2008

[10] J Zhang ldquoEffects of particle crushing and dilatation on theshear strength of calcareous sandrdquo Rock and Soil mechanicsvol 30 no 7 pp 2043ndash2048 2009

[11] P Zhang B Luo and P Liu ldquoInfluence of moisture contenton the strength characteristics of red clayrdquo Hydroelectricityvol 45 no 5 pp 45ndash49 2019

[12] T Zhang and D Sun ldquoRelationship between shear strengthandmoisture content of guilin compacted red clayrdquo Journal ofShanghai University (Natural Science Edition) vol 20 no 05pp 586ndash595 2014

[13] J Xu and S Pan ldquoExperimental study on mechanical prop-erties of soft soil changing with water contentrdquo Journal ofHuazhong University of Science and Technology vol 19 no 2pp 10ndash12 2002

[14] J Li ldquoStress-strain characteristics of clay with differentmoisture content under different test conditionsrdquo Journal ofGeotechnical Engineering vol 28 no 3 pp 343ndash347 2006

[15] Y Feng and Y Zhang ldquoExperimental study on stress-water-strain relationship of remolded loess under directional shearstress pathrdquo Journal of Qinghai University vol 36 no 1pp 47ndash53 2018

[16] C Xiao X Li and J Zhang ldquoEffect of compaction degree andwater content on performance of sandy siltrdquo Journal ofShenzhen University Science and Engineering vol 34 no 5pp 501ndash508 2017

16 Advances in Civil Engineering

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17

[17] S Wang X Lei Q Meng J Xu M Wang and W GuoldquoModel tests of single pile vertical cyclic loading in calcareoussandrdquo Marine Georesources amp Geotechnology pp 1ndash12 2020

[18] Y Shen F Zhaoyan H Liu and An Li ldquoExperimental studyon influence of initial concentration on settling velocitycharacteristics of turbidified liquid in coral mud deposition inthe south China seardquo Journal of Geotechnical Engineeringvol 40 no S2 pp 22ndash26 2018

[19] Y Shen Geotechnical Engineering Testing Technology Met-allurgical Industry Press Beijing China 2017

[20] J L Wang V Vivatrat and J R Rusher ldquoGeotechnicalproperties of Alaska oes siltsrdquo in Proceedings of the 14thAnnual Offshore Technology Conference OTC 4412 HoustonTX USA June 1982

[21] S Iravani Geotechnical Characteristics of Penticton SiltUniversity of Alberta Edmonton Canada 1999

[22] T L Brandon A T Rose and J M Duncan ldquoDrained andundrained strength interpretation for low-plasticity siltsrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 132 no 2 pp 250ndash257 2006

[23] Z Zhu and S Liu ldquoTriaxial test of silt and its stable soilrdquo Rockand Soil Mechanics vol 26 no 12 pp 1967ndash1971 2005

[24] X Tu and S Wang ldquoDescription of particle shape parametersin image analysisrdquo Journal of Geotechnical Engineeringvol 26 no 5 pp 659ndash662 2004

[25] C F Mora and A K H Kwan ldquoSphericity shape factor andconvexity measurement of coarse aggregate for concrete usingdigital image processingrdquo Cement and Concrete Researchvol 30 no 3 pp 351ndash358 2000

[26] M L Hentschel and N W Page ldquoSelection of descriptors forparticle shape characterizationrdquo Particle amp Particle SystemsCharacterization vol 20 no 1 pp 25ndash38 2003

[27] l Jiang Study on Mechanical Properties of Calcareous Sand inSouth China Sea Chengdu University of technologyChengdu China 2014

[28] M Jiang ldquoA new perspective of modern soil mechanics re-search -- macro and micro soil mechanicsrdquo Journal of Geo-technical Engineering vol 41 no 2 pp 195ndash254 2019

[29] G Li Higher Soil Mechanics tsinghua university press Bei-jing China 2nd edition 2016

[30] M Braja Das Advanced Soil Mechanics e University ofTexas El Paso TX USA 1983

[31] J Qian and Z Yin Geotechnical Principle and CalculationChina water resources and hydropower press Beijing China2nd edition 2000

[32] K Wang Triaxial Experimental Study on Consolidation andUnloading Strength Characteristics of Silt in HangzhouZhejiang University of Science and Technology ZhejiangChina 2019

[33] H Bingbing Experimental Study on Small Strain ShearModulus and Shear Characteristics of Anisotropic Super-consolidated Wenzhou Soft Clay Harbin Institute of Tech-nology Harbin China 2018

[34] Y Xiao and S M ASCE ldquoStrength and deformation of rockfillmaterial based on large-scale triaxial compression tests Iinfluences of density and pressurerdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 140 no 12 Article ID04014070 2014

[35] K H Roscoe A N Schofield and Aurairajah ldquoYielding ofclays in states wetter than criticalrdquo Geotechnique vol 13no 3 pp 211ndash240 1963

Advances in Civil Engineering 17