Mechanical Parameters and Bearing Capacity of … that the allowable bearing pressure and the...

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094

© Research India Publications. http://www.ripublication.com

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Mechanical Parameters and Bearing Capacity of Soils Predicted from

Geophysical Data of Shear Wave Velocity

Qassun S. Mohammed Shafiqu a, Erol Güler b and Ayşe Edinçliler c

aAssistant Professor, Dr., Civil Engineering Department, Al-Nahrain University, College of Engineering, Baghdad, Iraq. Professor, Dr, Civil Engineering Department, Bogazici University, College of Engineering, Istanbul, Turkey.

Professor, Dr, Earthquake Engineering Department, Bogazici University, College of Engineering, Istanbul, Turkey.

aORCID: 0000-0002-0389-6872

Abstract

The analysis of foundation vibrations and earthquake problems

in geotechnical engineering demands characterization of

dynamic soil properties by geophysical techniques. Also the

dynamic structural analysis of the superstructures needs

knowledge of the dynamic response of the soil-structure,

which, in turn depends on dynamics properties of soil. The

estimation of seismic velocities, modulus of elasticity and

structural properties of soils is not enough in the design of

engineering projects. Therefore, an ultimate bearing capacity

has been predicted using the seismic shear wave velocity. It is

indicated that the allowable bearing pressure and the coefficient

of subgrade reaction together with many other elasticity

parameters may be obtained rapidly and reliably once the

seismic wave velocities are determined in situ by convenient

geophysical survey. In this study, S-wave and P-wave

velocities data were obtained from seismic borehole survey in

the foundation layers of Iraq. Use was made of the existing

mathematical relations between various parameters and seismic

wave velocities for the study of foundation layers in the study

areas. Based on the results, the elastic constants, allowable

bearing capacity, and other parameters were determined and

evaluated. It was indicated that for cohesive and cohesionless

soils, up to a shear wave velocity of 300 m/s and 400 m/s

respectively, the shear wave velocity may predicts the bearing

capacity relatively well.

Keywords: Bearing capacity, soil parameters, shear wave

velocity, seismic technique, shear modulus.

INTRODUCTION

A footing is the supporting base of a building which forms the

interface across which the loads are transmitted to the

sublayers. If the structural loads are transmitted to the near-

surface soil, then it is referred to as shallow foundation.

Earthquakes may cause a reduction in bearing capacity and

increase in settlement and tilt of shallow foundations due to

seismic loading. The foundation must be safe both for the static

as well for the dynamic loads imposed by the earthquakes. Soil-

foundation-structure system should work together in a coherent

manner. In particular, if the site is exposed to high seismic

loadings it is highly desirable that the soil-foundation part of

the system should play an appropriate role in delivering the

required overall performance.

In the design of shallow foundation one of the main factors

related to soil is bearing capacity and the other is settlement or

in other words the subgrade reaction. The seismic S-wave

velocity is an effective parameter for estimating the bearing

capacity of soils [1]. Elastic parameters such as Young’s

modulus, Bulk modulus, shear modulus, Poisson’s ratio,

Oedometric modulus and others are related to shear wave

velocity leading to the determination of allowable bearing

capacity for shallow foundations [2].

For the calculation of allowable bearing capacity, the

geophysical methods, utilising seismic wave velocity

measuring techniques with absolutely no disturbance of natural

site conditions, may yield relatively more realistic results than

those of the geotechnical methods, which are based primarily

on bore hole data and laboratory testing of so-called

undisturbed soil samples [3].

Many researchers have extensively studied to obtain a relation

between the various parameters of soil mechanics and the

seismic wave velocities. Hardin and Black [4], and Hardin and

Drnevich [5] established indispensable relations between the

shear wave velocity, void ratio, and shear rigidity of soils based

on extensive experimental data. Also, Ohkuba and Terasaki [6]

supplied different expressions relating the seismic wave

velocities to density, permeability, water content, unconfined

compressive strength and modulus of elasticity. Also the use of

geophysical methods in foundation engineering has been

extensively investigated [7, 8, 9, 10, 11 and 12].

Keçeli [10 and 13] indicated that the determination of the

allowable bearing capacity could be obtained by means of the

seismic technique. Tezcan et al. [2]; Kaptan et al. [14] has

defined an allowable bearing capacity and a settlement as

depending on the layer thickness. But, it is well known that the

soil bearing capacity, settlement and modulus of elasticity

cannot be dependent on the layer thickness. Nevertheless, they

obtained also an allowable bearing capacity by changing the

notation of the relations in the article of Keçeli [13].

GEOLOGY AND SEISMISITY OF THE STUDY AREA

Iraq lies at the north east comer of the Arabian Peninsula. It is

a land of contrasting geography with an arid desert in the west

and the rugged mountains of the Taurus and Zagros in the north

east, separated by the central fertile depression of

Mesopotamia: long known as the cradle of civilization. This

mailto:[email protected]



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morphology facilitated early human migration and dispersion

of knowledge between the East and West. Sumerian cities as

old as 6000 years are a witness not only to a thriving early

civilisation but also to the early industrial use of raw-materials.

With respect to geological terms Iraq lies at the transition

between the Arabian Shelf in the west and the intensely

deformed Taurus and Zagros Suture Zones in the north and

north east. The evolution of the Arabian Shelf has been effected

by the mobility of the Precambrian basement and by tectonism

along the Neo-Tethyan margin. The tectonic framework of Iraq

has been affected by intracratonictranspressional and

transextensional movements controlled by the interactions of

stress along the plate margin with the Precambrian basement

fabric and structural grain.

After 1900, earthquakes in Iraq were better known in amounts

ranging from (M=2.7 to 7.2) within the geographical

boundaries of Iraq's earthquake map, with the majority of

shocks deep in the Earth's crust. The earthquakes in Iraq have

a general and distinct increase from the west to the east and

from the south to the north. The eastern side of the study area

is a relatively wide zone of compressional deformation along

the Zagros – Taurus active mountain belt, which is entrapped

between two plates, the Arabian in the southwest and the

Iranian plate in the northeast [15], although the territory of Iraq

not directly located on a dense cluster of recent earthquake

epicenters; But geodynamic formations for high seismic risks

show medium. This will be coupled with the increasing

vulnerability of the major highly populated cities. Over the past

two decades, the state of seismological research, seismic

monitoring and earthquake risk education has seen better times

[16].

Tectonically the study area is in a relatively active seismic zone

at the northeastern boundaries of the Arabian Plate. The

corresponding Zagros - Tauros Belts manifest the subduction

of the Arabian plate into the Iranian and Anatolian Plates .The

seismic history reveals annual seismic activity of various

strength. The north and northeastern zones shows the largest

seismic activity with strong diminution in the south and

southwestern parts of the country.

The geodynamic configurations of Iraq show a medium to high

seismic risk, although the territory of Iraq not directly located

on a dense cluster of recent earthquake epicenters. This will be

coupled with the increasing vulnerability of the major highly

populated cities. The state of seismological research, seismic

monitoring, and seismic hazard awareness have seen better

times during the last two decades.

THEORY

The response of soils to dynamic loading is controlled mostly

by the mechanical properties of the soil. Many types of

geotechnical engineering problems are associated with

dynamic loading, such as: machine vibrations, seismic loading,

liquefaction and cyclic transient loading, etc. The dynamic soil

parameters related with dynamic loading are shear wave

velocity (Vs), damping ratio (D), shear modulus (G), and

Poisson’s ratio (ν), which are also used in many non-dynamic

type problems. The problem of predicting the bearing capacity

of soils from wave propagation properties is that the soil

undergoes only very low strain during the wave propogation.

However when soils are subjected to earthquake loads or static

loads upto failure, they undergo large strains.

The P and S-wave velocities are usually denoted by Vp and Vs respectively. Once the seismic wave velocities are measured,

shear modulus (G), Bulk modulus (K), Young’s modulus or

modulus of elasticity (E), Poisson’s ratio (ν), Oedometric

modulus (Ec) and other elastic parameters may be obtained

from the Equations (1) to (8) below. These expressions make

the determination of the allowable bearing capacity possible.

1) Shear modulus (G) relates with shear wave velocity as

expressed in Equation (1):

G = ρ Vs2 (1)

Where ρ is the mass density equal to ρ = γ/g , γ is the unit weight

of the soil and gis the acceleration due to gravity which isgiven

as 9.8g m.s2.

The unit mass density relates with P-wave velocity Vpas shown

in Equation (2)

γ = γ0+ 0.002 Vp (2)

Tezcan et al., [2] defines γo as the reference unit weight value

in kN/m3.γo= 16 for loose, sandy and clayey soil. According to

[17], some elastic parameters were defined in Equations (3) to

(9):

2) Young’s modulus/modulus of elasticity (Ed)

E = ρ Vp2 (3)

3) Oedometric modulus (Ec) given by Equation (4)

Ec = E (1-v)/(1+v)(1-2v) (4)

4) Bulk modulus (K) is expressed in Equation (5) as

K =2(1+v)G / 3(1-2v) (5)

5) Poisson’s ratio (ν) is given as in Equation (6) as

ν=(α -2) / 2(α-1) (6)

where α= Ec / G= (Vp / Vs)2 (7)

6) Subgrade Coefficient ks, ultimate bearing capacity qult and

allowable bearing capacity qall are given by Equations (8) to

(10) according to [18] and [19] as,

ks = 4 γ Vs = 40 qult (8)

7) Ultimate Bearing Capacity (qult)

qult=ks/40= 4 γ Vs/40=0.1 γ Vs (9)

for shallow foundation [18]

8) Allowable Bearing Capacity (qall)

qall=qult / n =0.1 γVs / n (10)

Where n is the factor of safety (n = 4.0 for soils)



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Low compressibility and compliance and high bearing capacity

are required in construction or foundation sites which can be

determined from the reciprocal values of bulk modulus (K) and

Young’s modulus (E) respectively. Shear modulus and shear

wave velocity of the soil layer is reduced with increasing shear

strain [20].

MATERIALS AND METHODS OF DATA ANALYSIS

Resources of Geophysical and Geotechnical Data

For many projects in Iraq the engineering parameters of the

different strata from many geophysical and geotechnical

investigation reports are collected [21], and a data base is

prepared for static, shear and compression wave velocities

parameters of different soils for most zones in Iraq. The

available geotechnical and geophysical reports were collected

from different forty nine projects like gas power station, cement

plant, multi-story buildings, thermal Power plant, water

sewerage system, oil refinery and other projects from different

locations of Iraq and the data has been grouped into nine

regions, based on the governorates, namely (North, Eastern

North, Western North, Middle, East, West, Western South,

Eastern South and South) as shown in Table (1) and Figures

(1 and 2), where the zones borders are according to the

governorate boundaries. These parameters are evaluated from

field and laboratory tests results of the available geotechnical

and geophysical investigation reports collected from different

resource such National Center of Construction Laboratories

and Research (NCCLR), engineering consulting bureaus of

Baghdad and Al-Nahrain universities together with some

private companies and laboratories such as Andrea Engineering

Test labs, AL-Ahmed Engineering Test lab and others.

When the seismic wave velocities, Vs and Vp, are obtained,

several parameters of elasticity, like shear modulus G,

oedometric modulus of elasticity Ec , modulus of elasticity E

(Young’s modulus), bulk modulus K, and Poisson’s ratio ν may

be obtained from the Equations (1) to (7). Also the subgrade

modulus ks, ultimate and allowable bearing capacities are

onbtained depending on the Equations (8), (9) and (10)

respectively and as will be presented in Table (2).

Figure 1. Map study of seismic zones in Iraq [21 Figure 2. Map study of projects locations in Iraq [21]



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Table 1: Iraq seismic zones and sites symbols according to [21]

NO. Zone Governorate Site

symbol

Map

symbol

NO. Zone Governorate Site

symbol

Map

symbol

1

North

Dohuk N1 1 26 Middle Babylon M10 26

2 Dohuk N2 2 27 East

Diyala E1 27

3 Irbil N3 3 28 Diyala E2 28

4 Irbil N4 4 29 West Anbar W2 30

5

Eastern

North

Sulaymaniyah EN1 5 30

Western

south

Karbala WS1 31

6 Sulaymaniyah EN2 6 31 Karbala WS2 32

7 Kirkuk EN3 7 32 Karbala WS3 33

8 Kirkuk EN4 8 33 Karbala WS4 34

9 Kirkuk EN5 9 34 Najaf WS5 35

10 Kirkuk EN6 10 35 Najaf WS6 36

11 Kirkuk EN7 11 36

Eastern

South

Missan ES1 37

12

Western

North

Mosul WN1 12 37 Missan ES2 38

13 Mosul WN2 13 38 Missan ES3 39

14 Mosul WN3 14 39 Missan ES4 40

15 Salah Al-den WN4 15 40

South

Al Dewaniya S1 41

16 Salah Al-den WN5 16 41 Al Dewaniya S2 42

17 Baghdad M1 17 42 Al Nasiriya S3 43

18

Middle

Baghdad M2 18 43 Al Nasiriya S4 44

19 Baghdad M3 19 44 Al Nasiriya S5 45

20 Baghdad M4 20 45 Al Basrah S6 46





25 Babylon M9 25

Investigated Soil Parameters

The data for soil parameters investigated were taken from

geotechnical and geophysical investigation reports for most

Iraqi soil. Soil parameters such as; γwet ,γdry, c and ϕ which are

given in the geotechnical reports had evaluated by the field or

laboratory tests, also the depth of the water table and

description of the soil types according to borehole logs were

presented in these reports. While the seismic wave velocities

Vs, Vp values are listed in the geophysical reports that been

evaluated from the cross hole and down hole tests. The

geotechnical bore hole should be the same for the geophysical

bore hole or might be different bore hole but they should be

near to each other or collected either from the same borehole or

two adjacent ones which have the same soil layers profile.

The soil strength parameters (c or ϕ ) were evaluated by the

correlations from N value (SPT) according to the type of soil

when their values are not mentioned or evaluated in some of

the soil investigation reports.

Soil Parameters Evaluation

As mentioned earlier the soil parameters γwet ,γdry , c, ϕ

determined from field and laboratory tests results are presented

in the geotechnical investigation reports, and the dynamic

parameters Vs and Vp are prepared from geophysical

investigations reports. Once seismic wave velocities, Vp and Vs

, together with the density are measured, many parameters of

elasticity, such as shear modulus G, oedometric modulus of



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elasticity Ec , modulus of elasticity E (Young’s modulus), bulk

modulus K, and Poisson’s ratio ν may be obtained from the

Equations (1) to (7). Also the subgrade modulus ks, ultimate

and allowable bearing capacities are obtained depending on the

Equations (8), (9) and (10) respectively.

able (2) presents the geotechnical and geophysical parameters

collected and evaluated together with the values of ks, qult and

qall estimated.

Table 2: Soil properties and bearing capacity in different locations and zones of Iraq.

No. Site

Depth Soil Type WT γwet γdry c ϕ Vp Vs E×103 G×103 ν K×106 Ks×108 qult

1×102 qall

1×102 qult

2×102 qall

2×102 qall

2×102

m m kN/m3 kN/m3 kN/m2 (o) m/s m/s kN/m2 kN/m2 kN/m2 N/m2.s kN/m2 kN/m2 kN/m2 n=4 n=3

1 N1 0-3 Brown silty clay

with little fragment

NO

W.T

18.4 15.3 32 17 992 302 501.95 171.55 0.463 6.62 0.2223 5.56 1.39 4.87 1.22 1.62

3-10 Dense grey gravel with sand to gravel

with silt and sand

(GP,GP-GM)

19 14.9 0 42 1445 468 1233.6 422.46 0.46 5.14 0.3557 8.89 2.22 16.34 4.08 5.45

2 N2 0-7.5 Reddish brown rock

fragment of

limestone with silty

sand

>25 19.6 16.8 0 39 1623 832 3642.64 1354.1 0.345 39.17 0.6523 16.31 4.08 9.31 2.33 3.1

3 N3 4-10 Brown silt/clay with few sand & trace of

gravel,(CL-ML)

No W.T

21.3 18.1 49 28 807 354 706.4 248.56 0.421 1.5 0.3016 7.54 1.89 16.95 4.24 5.65

4. N4 0-6 Brown silt/clay with

few sand,(CL)

21.4 18.1 43 21 988 296 517.13 178.32 0.45 1.72 0.2534 6.33 1.58 8.6 2.15 2.87

6-10 Brown silt/clay with little sand& few

gravel,(CL-ML)

21.2 17.8 35 34 1460 462 1204.83 413.75 0.456 4.56 0.3918 9.79 2.45 22.45 5.61 7.48

5. EN1 0-4 Unknown 19.9 16.6 94 0 1745 262 419.05 144 0.486 5.13 0.2086 5.21 1.30 5.36 1.34 1.79

4-15 Unknown 20.9 18.4 0 44 2606 576 1963.11 670.6 0.463 8.84 0.4815 12.04 3.01 27.33 6.83 9.11

6 EN2 0-5 Unknown 19.4 17.6 81 3 1485 233 336.53 113.62 0.481 2.95 0.1808 4.52 1.13 4.62 1.16 1.54

5-10 Unknown 21.6 18.1 4 42 2313 384 932.18 283.48 0.467 4.2 0.3318 8.29 2.07 18.57 4.64 6.19

7 EN3 0-4 Stiff brown lean to

fat clay (CL, CH)

3.9 19.7 16.8 55 0 535 219 253.86 90.6 0.401 0.43 0.1726 4.31 1.08 3.14 0.79 1.05

4-6 Medium brown silty

Sand (SM)

19.6 17.2 21 33 679 301 477.75 172.47 0.385 0.69 0.2359 5.9 1.48 3.13 0.78 1.04

6-12 Dense grey gravel with sand to gravel

with silt and

sand(GP, ,GP-GM)

19.5 16.8 0 42 1384 733 2760.89 991.7 0.392 4.26 0.5717 14.29 3.57 16.77 4.19 5.59

8

EN4

0-2 Brown silt with

(ML)

2.9 19.4 17.7 5 37 360 145 124.2 44.25 0.403 0.21 0.1125 2.81 0.7 6.33 1.58 2.11

2-6 Stiff brown lean clay

(CL)

17.3 15.8 80 0 514 212 284.06 98.44 0.392 0.42 0.1467 3.67 0.92 4.56 1.14 1.52

6-15 Stiff brown to grey lean clay (CL)

19.4 17.5 21 39 1065 323 663.2 229.3 0.424 1.43 0.2506 6.27 1.57 9.22 2.3 3.07

9

EN5 0-2.5 Stiff brown sandy silt (ML)

>25 19 16.8 0 32 1125 225 290.15 98.09 0.479 2.3 0.1710 4.28 1.07 2.55 0.63 0.85

2.5-15 Very stiff to hard

brown lean to fat

CLAY (CL,CH)

20.6 18.2 227 0 1250 321 634.86 216.38 0.467 3.21 0.2645 6.61 1.65 12.94 3.24 4.31

15-20 Very dense silty

gravel with sand (GM)

20.6 18.2 0 42 2500 476 1409.8 475.9 0.481 12.37 0.3922 9.81 2.45 17.71 4.43 5.9

1seismic method [17]

2conventional method [18]



1080

Table (2): Continue

No. Site

Depth Soil Type WT γwet γdry c ϕ Vp Vs E×103 G×103 ν K×106 Ks×108 qult1×102

qall1×102

qult2×102

qall2×102

qall2×102

m m kN/m3 kN/m3 kN/m2 (o) m/s m/s kN/m2 kN/m2 kN/m2 N/m2.s kN/m2 kN/m2 kN/m2 n=4 n=3

10 EN6 0-10 Stiff to very stiff

brown lean or fat clay (CL,CH)

2.6 21.0 18.1 120 0 1541 304 585.82 197.91 0.48 4.88 0.2554 6.39 1.6 6.84 1.71 2.28

11 EN7 0-10 Very stiff to hard brown lean clay

(CL)

3.8 20.1 17 130 0 1250 312 585.43 199.53 0.467 2.96 0.2508 6.27 1.57 7.41 1.85 2.47

12 WN1 0-15 Very Stiff to hard

moderately

gypseous, brown lean to fat clay

(CL,CH)

2.8 19 17.3 65 0 1330 459 1069.8 378.56 0.413 2.05 0.3488 8.72 2.18 3.71 0.93 1.24

13 WN2 0-7.5 Dark brown sand silt

with rock fragments

>25 18.3 16 0 37 773 319 542.6 189.3 0.432 1.33 0.2335 5.84 1.46 5.97 1.49 1.99

7.5-20 Brown sand gravel 17.8 15.3 0 42 1113 348 600.3 202.5 0.416 1.14 0.2478 6.2 1.55 15.3 3.83 5.1

14 WN3 4-15 Medium dense to

very dense grey silty

gravel with sand (GM,GP)

2.3 19.4 16.3 0 38 1057 362 584.6 217.2 0.424 1.36 0.2809 7.02 1.76 7.63 1.91 2.54

15 WN4 0-2 Grey gravel with silt sometimes with

sand(GM)

No W.t

18.3 16.8 0 36 714 292 445.39 160.21 0.39 0.67 0.2137 5.34 1.34 4.57 1.14 1.52

2-5 Medium stiff to hard

brown lean clay

sometimes with sand and gravel to

silt(CL,ML)

20.1 15.3 46 34 1055 346 676.62 238.08 0.421 1.43

0.2782

6.96

1.74

28.03 7.0 9.34

5-10 Dense to very dense

grey gravel with silt and sand to gravel

17.8 16.1 0 43 1335 606 2009.1 714.45 0.406 3.56 0.4315 10.79 2.7 18.83 4.71 6.28

16 WN5 0-4 Highly gypseoussilty sand to sandy silt

with little gravel

16 18.4 15.9 0 37 942 451 1030.4 374.97 0.374 1.36 0.3319 8.3 2.07 6 1.5 2

4-20 Silty sand with

gravel to sand with

gravel

19 14.8 0 41 1373 701 2559.4 916.7 0.396 4.1 0.5328 13.32 3.33 13.35 3.34 4.45

17 M1 0-10 Stiff to very stiff brown to green

slightly

gypseousmarly lean to fat clay and silt

clay (CL,CH,CL-

ML)

2.1 18.7 14.8 76 12 544 186 187.1 64.84 0.446 0.578 0.1391 3.48 0.87 4.33 1.08 1.44

10-16 Loose to medium

grey to green silty sand (SM)

20 16.3 0 36 736 258 381.9 140.42 0.433 1.0 0.2064 5.16 1.29 5.44 1.36 1.81

18

M2 0-8 Medium to stiff to very stiff brown lean

clay (CL)

2.65 20.1 17 125 0 820 265 414.42 144.1 0.438 1.11 0.2131 5.33 1.33 6.42 1.61 2.14

8-15 Loose to dense grey

silty sand to clayey

silty sand

19.1 15.5 0 36 1150 395 815.79 283.26 0.44 2.27 0.3018 7.55 1.89 5.19 1.3 1.73

19 M3 0-10 Soft to stiff brown

lean or fat clay or silt sometimes lean clay

with sand to sandy

silt (CL,CH,ML)

0.8 18.7 14.9 52 12 443 153 146.53 45.52 0.43 0.31

0.1144 2.86 0.72 2.67 0.67 0.89

10-18 Medium to very dense grey silt sand

or clayey sand

(SM,SC)

19 14 0 39 769 215 263.34 91.12 0.445 0.8 0.1634 4.1 1.02 9.03 2.26 3

20

M4

0-10 Stiff to very stiff

brown lean clay

1.55 19.78 17.43 180 0 761 298 538.8 191.5 0.408 0.98 0.2358 5.9 1.47 9.25 2.31 3.08



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10-15 Stiff to very stiff grey to brown to

black lean clay

sometimes with sand (CL)

1.55 20.2 17.1 68 16 1113 428 995.34 373.2 0.415 2.1 0.3458 8.65 2.16 9.48 2.37 3.16

15-20 Medium grey silty

sand (SM)

20.89 17.02 0 34 1351 507 1388.6 511.6 0.417 2.9 0.4236 10.59 2.65 3.97 0.99 1.32

21 M5 10-15 Loose to medium

grey silty sand (SM)

3.1 18.4 15.6 0 38 1191 430 977.68 336.2 0.454 3.5 0.3165 7.91 1.98 7.23 1.81 2.41

22 M6 0-1 Brown clayey silt to

sandy silt with filling materials, organic to

salts (ML)

1.3 19.00 15.8 28.7 0 322 140 251.99 91.1 0.383 0.36 0.1064 2.66 0.67 1.48

0.37 0.49

1-15 Brown to grey silty

clay to clayey silt (ML,CL,CH)

18.88 14.7 31.5 0 776 219 403.34 138.51 0.456 1.53 0.1654 4.14 1.03 1.62 0.41 0.54

15-20 Grey sand to silty or

clayey sand to

gravilly sand

(SM,GP)

22.31 17.04 0 38 1504 408 941.3 321.92 0.462 4.13 0.3641 9.10 2.28 8.77 2.19 2.92

23 M7 0-6 Medium stiff to stiff brown fat clay (CH)

0.6 19.8 15.8 50 0 641 189 209.16 72.13 0.45 0.7 0.1497 3.74 0.94 2.57 0.64 0.86

6-12 Very stiff brown lean clay (CL)

19.0 14.5 100 0 675 248 338.44 119.17 0.42 0.71 0.1885 4.71 1.18 5.14 1.29 1.71

12-15 Medium dense to

dense silty sand to

silty sand with gravel

19.0 15.0 0 37 750 225 284.46 98.09 0.45 0.95 0.1710 4.28 1.07 6.2 1.55 2.07

24 M8 Stiff to very stiff brown lean to fat

CLAY(CH)

19.8 17.1 65 10 841 165 162.7 54.97 0.48 1.36 0.1307 3.27 0.82 6.3 2.1

0-7.5 1.58

7.5-12 Medium to very

dense grey silty sand

(SM)

2.2 19.0 16.5 0 38 1025 279 440.3 150.8 0.46 1.83 0.2120 5.3 1.33 7.47 1.87 2.49

25 M9 0-5 Very soft to stiff brown lean to fat

clay sometimes with sand (CL,CH)

1.41 21.26 17.85 90 0 735 260 406.11 145.35 0.397 0.66 0.2211 5.53 1.38 4.63 1.16 1.54

5-15 Losse to dense grey

silty SAND(SM)

18.6 15.4 0 38 1503 369 682.46 242.5 0.403 1.17 0.2745 6.86 1.72 7.31 1.83 2.44

26 M10 0-2.4 Grayish sandy silty

clay soil, medium

consistency

1.5 16.18 14.5 144 0 306 111 57.9 20.33 0.424 0.13 0.0718 1.8 0.45 7.4 1.85 2.47

2.4-15 Grayish silty sand

soil, medium dense

18.44 16.5 0 38 450 183 176.33 62.98 0.4 0.29 0.1350 3.38 0.84 7.25 1.81 2.42

27 E1 0-10 Very stiff to hard

brown to grisg

brown marl lean clay (CL)

1.72 21.1 18.3 83 0 976 372 835.49 298.82 0.398 1.37 0.3140 7.85 1.96 4.27 1.07 1.42

28 E2 0-15 Stiff brown clay (CL)

1.46 20.3 17.1 76 0 1076 398 945.39 331.95 0.424 2.07 0.3232 8.08 2.02 3.9 0.98 1.3

29 W2 0-5 Stiff to very stiff brown lean clay(CL)

1.75 20.4 17.07 120 0 730 257 386.09 135.85 0.421 0.81 0.2097 5.24 1.31 6.17 1.54 2.06

5-10 Loose to dense grey to dark grey silty

sand and clayey silty

sand sometimes with gravel (SM,SC-SM)

18.2 15.2 0 33 1513 379 809.19 282.34 0.433 2.01 0.2759 6.9 1.72 2.91 0.73 0.97

30 WS1 0-5 Stiff brown to green 1.2 19.5 15.6 77 0 688 198 223.14 72.87 0.458 0.84 0.1544 3.86 0.97 3.96 0.99 1.32



1082

lean clay

5-9 Loose to medium

brown to grey silty sand (SW-SM)

18.4 14.8 0 33 948 265 401.85 137.62 0.46 1.67 0.1950 4.88 1.22 2.94 0.73 0.98

9-15 Very dense grey silty

sand

19.1 15.3 0 36 1370 497 1329.6 463.92 0.433 2.29 0.3797 9.49 2.37 5.19 1.3 1.73

31 WS2 0-18 Loose to very dense off white yellow,

light brown to grey

sometimes moderately

gypseoussilty sand

or sand with silt or sand (SM,SP-

SM,SP)

NO W.T

19.6 17.93 0 38 986 417 958.17 340.98 0.405 1.68 0.3270 8.18 2.04 7.7

1.93 2.57

32 WS3 0-10.5 Stiff brown silty to

moderately gypseous fat clay (CH)

1.5 18.5 14.7 100 0 1416 312 541.76 183.65 0.475 3.61 0.2309 5.77 1.44 5.14 1.29 1.71

33 WS4 0-4.5 Dense white to yellow slightly to

moderately gypseous

sand with silt to silty sand with gravel

(SP,SM)

0.8 18.8 18 0 37 1433 284 457.0 154.6 0.478 3.46 0.2136 5.34 1.34 6.14 1.53 2.05

4.5-12 Dense to very dense

white to yellow sand with silt (SP,SM)

19.4 18 0 35 1733 550 1727.2 598.46 0.443 5.05 0.4268 10.67 2.67 4.4 1.1 1.47

12-22 Very dense white to

yellow sand with silt

to silty sand (SP,SM)

19.4 18 0 35 1650 563 1801 627.1 0.436 3.71 0.4369 10.92 2.73 4.4 1.1 1.47

34 WS5 0-10 Very loose grading to very dense

slightly to

moderately gypseous sand (sm) or sand

with silt (SP-SM)

2.1 17.5 14.9 0 41 1613 618 1975.9 696.75 0.4185 4.04 0.4326 10.82 2.70 12.29 3.07 4.1

35 WS6 0-1.2 Medium- dense light

brown slightly

gypseoussilty sand (SM)

0.9 19.1 17 0 43 805 268 412.33 143.37 0.438 1.11 0.2048 5.12 1.28 20.15 5.03 6.71

1.2-7 Medium- dense to

very dense light

brown sand (SP)

19.5 18 0 40 1450 557 1743.5 616.95 0.413 3.34 0.4345 10.86 2.72 11.24 2.81 3.75

7-10 Very dense light

brown silty sand (SM)

19.6 18 0 39 1812 659 2472.2 868.03 0.424 5.42 0.5167 12.92 3.23 9.31 2.33 3.1

36 ES1 0-6 Stiff to very stiff brown to green

sandy lean to fat

CLAY (CL,CH)

0.41 19.2 14.8 53 4 451 111 69.32 23.67 0.464 0.32 0.08525 2.13 0.53 3.7 0.93 1.23

6-14 Loose grey silty sand (SM)

20.45 17.8 0 36 605 152 167.53 57.49 0.457 0.65 0.1243 3.11 0.78 5.56 1.39 1.85

14-20 Stiff to very stiff

brown to green fat

clay (CH)

19.9 15.6 63 0 690 211 254.57 89.07 0.429 0.61 0.1680 4.2 1.05 3.24 0.81 1.08

37

ES2 0-5 Medium stiff to stiff

brown lean to fat clay (CL,CH)

0.6 18.0 14.6 65 0 377 131 90.15 31.5 0.431 0.22 0.0943 2.36 0.59 3.34 0.84 1.11

5-8

Stiff brown lean to fat clay (CL,CH)

19.5 15.8 60 0 604 250 347.98 124.28 0.4 0.58 0.1950 4.88 1.22 3.08 0.77 1.03

8-17 Stiff brown lean clay (CL)

20.8 15.9 60 8 1362 420 1082.8 374.17 0.447 3.41 0.3494 8.74 2.18 5.2 1.3 1.73



1083

38 ES3 0-9 Medium stiff to stiff brown lean to fat

clay (CL,CH)

0.6 19.7 15.7 80 0 696 179 188.5 64.37 0.464 0.87 0.1411 3.53 0.88 4.11 1.03 1.37

9-18 Stiff brown lean

CLAY (CL)

20.9 16.1 60 0 1167 380 886.78 307.76 0.44 2.46 0.3177 7.94 1.99 3.08 0.77 1.03

39 ES4 0-7.5 Medium stiff to stiff


0.6 19.5 15.1 80 0 500 176 175.96 61.57 0.429 0.41 0.1373 3.43 0.86 4.11 1.03 1.37

7.5-9 Loose grey silty sand 19.5 15.7 0 29 600 200 228.51 79.51 0.437 0.6 0.1560 3.9 0.98 1.58 0.39 0.53

9-10 Stiff brown lean clay (CL)

19.5 15.7 60 8 600 250 346.6 124.23 0.395 0.55 0.1950 4.88 1.22 5.2 1.3 1.73

40 S1 0-5 Stiff to very stiff brown to green

sandy lean to fat clay

(CL,CH)

0.3 19.6 15 42 8 685 225 281.99 99.02 0.424 0.62 0.1764 4.41 1.10 3.64 0.91 1.21

5-6.5 Loose grey silty sand (SM)

20.7 17.2 0 33 814 243 340.53 117.34 0.451 1.16 0.2012 5.03 1.26 3.31 0.83 1.1

6.5-10 Stiff to very stiff brown to green fat

clay (CH)

19.3 14.9 65 0 1224 333 645.63 220.2 0.466 3.16 0.2571 6.43 1.61 3.34 0.84 1.11

41 S2 0-1.5 Brown lean clay(CL) 0.3 18.5 14.4 94 0 625 188 193.28 66.65 0.450 0.64 0.1391 3.48 0.87 4.83 1.21 1.61

1.5-2 loose grey silty sand

layer (SM)

20.0 15.0 0 30 909 185 213.45 72.21 0.478 1.62 0.1480 3.7 0.93 1.91 0.48 0.64

2-10 Medium stiff to very

stiff brown to green

lean to fat clay (CL,CH)

19.3 14.7 60 5 909 200 232.17 78.73 0.475 1.55 0.1544 3.86 0.97 4.41 1.1 1.47

42 S3 0-8 Medium stiff to hard brown or grey or

dark grey lean to fat

clay sometimes with sand to sandy lean

clay or silt or sandy

silt(CL,CH,ML)

1.2 19.1 15.8 78 0 646 185 198.82 68.72 0.458 0.79 0.1413 3.53 0.88 4.0 1.0 1.33

8-15 Dense to very dense grey or dark grey or

brown silty sand

otsilty clayey sand or

sand with silt

(SM,SC-SM,SP-SM)

17.7 14.6 0 40 1094 321 562.51 198.94 0.464 2.7 0.2273 5.68 1.42 10.2 2.55 3.4

43 S4 0-12 Soft to medium

black, brown, green light, green lean to

fat clay (CL,CH)

1.7 19.5 15.2 90 3 434 110 70.54 24.06 0.466 0.35 0.0858 2.15 0.54 5.96 1.49 1.99

12-14 Loose grey silty sand

(SM)

20.8 18 0 41 500 145 129.7 44.6 0.454 0.47 0.1206 3.02 0.75 14.61 3.65 4.87

14-15 Very stiff brown,

green lean clay(CL)

20.8 17 191 0 600 166 170.56 58.45 0.459 0.69 0.1381 3.45 0.86 9.82 2.46 3.27

44 S5 0-4 Very stiff brown

lean clay (CL)

4 19.07 15.1 34 0 600 200 223.45 77.75 0.437 1.7 0.1526 3.82 0.95 1.75 0.44 0.58

4-10 Stiff to hard brown

lean to fat clay (CL,CH)

19.93 15 112 0 750 240 337.6 117.1 0.442 0.97 0.1913 4.78 1.2 5.76 1.44 1.92

45 S6 0-3 Medium light brown

gypseous soil

1.6 20.3 16.8 0 35 803 329 780.35 258.63 0.397 1.17 0.2671 6.68 1.67 4.61 1.15 1.54

3-10 Medium to very

dense light brown to

grey slightly to highly gypseoussilty

sand or sand with silt or sand (SM,SP)

18.9 16.01 0 34 1811 627 1797.46 737.98 0.446 6.59 0.4740 11.85 2.96 3.59 0.89 1.19

46 S7 0-3.7 Grey gypseous 1.8 18.18 16.1 5.33 39 566 230 269.05 96.012 0.401 0.45 0.1673 4.18 1.05 8.63 2.16 2.88



1084

sand (SM)

3.7-15 Grey gypseous silty sand (SM)

19.16 15.3 8.4 40 1404 365 750.38 256.45 0.463 3.38 0.2797 6.99 1.75 11.04 2.76 3.68

47 S8 0-6 Very soft to stiff brown lean clay

(CL)

5 21.1 16.4 60 0 434 166 168.06 59.47 0.412 0.32 0.1401 3.50 0.88 3.08 0.77 1.03

6-15 Very loose grey

clayey silty sand

(SC-SM)

19 15.3 0 37 510 194 250.53 88.4 0.417 0.50 0.1474 3.69 0.92 6.2 1.55 2.07

48 S9 0-6 Medium to stiff


1.1 19.7 15.7 80 0 294 117 82.58 29.47 0.401 0.14 0.0922 2.31 0.58 4.11 1.03 1.37

6-12 Stiff brown lean clay

(CL)

20.9 16.1 60 0 381 198 239.08 83.77 0.427 0.55 0.1655 4.14 1.03 3.08 0.77 1.03

49 S10 0-10 Very soft to stiff

brown lean or fat

clay(CL,CH)

1.0 18.37 13.92 40 0 550 138 104.6 35.7 0.466 0.51 0.1014 2.54 0.63 2.06 0.52 0.69

10-13 Grey silty sand (SM) 19.63 15.54 0 37 334 103 61.8 21.23 0.455 0.23 0.0801 2 0.5 6.4 1.6 2.13

13-15 Very soft to stiff lean

clay (CL)

20.02 16.03 48 0 450 102 62.57 21.24 0.473 0.39 0.0817 2.04 0.51 2.47 0.62 0.82

RESULTS AND DISCUSSION

Evaluation of the Allowable Bearing Capacity

In this research, geotechnical parameters, i.e. Young modulus,

bulk modulus, shear modulus, subgrade modulus were obtained

from the result of the secondary wave velocities for each layer

of the areas of study using Equations (1) to (8). These

relationships also led to the determination of the ultimate

bearing capacity and the allowable bearing capacity according

to the Equations (9) and (10) respectively. The results obtained

are presented in Table (2). Also, following the classical

procedure of [18], the ultimate and allowable bearing capacities

were determined, by assuming the factor of safety equal to n=3

and 4 and as given in Table (2) for the purpose of comparison.

The numerical values of the ultimate and allowable bearing

capacities determined in accordance with the conventional

Terzaghi theory and seismic technique (Tezcan et al., 2006) for

cohesive soils are plotted in Figures (3 and 4 respectively). And

the results of ultimate and allowable bearing capacities

estimated from both methods for cohesionless soils are plotted

in Figures (5 and 6 respectively).

Two separate linear regression lines were also shown in the

Figures (3 and 5), for the purpose of indicating the average

values of ultimate bearing pressure determined by ‘seismic’

and ‘conventional’ methods. For cohesive and cohesionless

soils it can be indicated that up to a shear wave velocity of 300

m/s and 400 m/s respectively, the shear wave velocity predicts

the bearing capacity relatively well. Above 300 m/s and 400

m/s the scatter is large and it looks like there are quite many

points that are falling below the bearing capacity estimated by

the shear wave velocity. The linear regression line indicates for

Vs values smaller than 300 m/s and 400 m/s a narrow band,

which should be regarded as quite acceptable. The ‘seismic’

method proposed herein yields allowable bearing cabacities (on

the order of 10 to 20%) greater than those of the ‘conventional’

method for Vs values smaller than 400 m/s. In fact, the

‘conventional’ method fails to produce reliable and consistent

results for relatively strong soils, because it is difficult to

determine the appropriate soil parameters c and ϕ for use in the

‘conventional’ method [22]. Therefore, from the results the use

of ‘seismic’ method can give an order of magnitude for such

strong soils with Vs > 300 m/s for cohesive soils and >400 m/s

for cohesionless soils.

The allowable bearing capacity has been obtained at different

sites in various regions of Iraq as shown in Table (2) and

Figures (4 and 6) for cohesive and cohesionless soils

respectively. Factor of safety used for allowable bearing

capacity estimated from shear wave velocity is 4 (Tezcan,

2006), and allowable bearing capacity is estimated from

Terzaghi equation using factor of safety, n=3 and 4, it can be

indicated that values from shear wave velocity are close to that

from conventional method till Vs=300 m/s for cohesive soils

and 400 m/s for cohesionless soils and above these velocities

the scatter is large. It can be concluded from these graphs that

allowable bearing capacity estimated from shear wave velocity

may be obtained for n less than 4 for soils that have Vs less and

equal than 400 m/s. Table (3) shows the range of values for

seismic wave velocities and allowable bearing capacity for

different types of soil with various description. In order to

demonstrate that the technique used covers all soils types, the

values of seismic velocities and allowable bearing capacity

given in Table (3) are compared with the values for foundation

materials given in building codes with entire seismic velocities

covering all soils and rocks types and with the values calculated

by using seismic velocities of soils and rocks [23] which has

been obtained at thousands of construction sites in various

regions of Turkey since 1990. The comparison shows that the

allowable bearing capacity values obtained from hard through

loose soils were in agreement with the building codes and

Keçeli [23] values. Thus, allowable bearing capacity values

obtained by the technique proposed here are evaluated for

accuracy. Table (3) also demonstrated awide range for soil

types description.

Allowable bearing capacity for cohesive and cohesionless soils

is plotted in each case against the shear wave velocity for each

of the layers as given in Figures (4 and 6 respectively) which

shows linear empirical relationships between the allowable



1085

bearing capacity and the shear wave velocity. This is

demonstrated in Equations (11 and 12):

For Cohesive Soils qall (kN/m2) =(0.0053Vs - 0.073)×102

(11)

For Cohesionless Soils qall(kN/m2)=(0.0048Vs + 4.0E-6)×102

(12)

The slopes in the equations are dimensionless constant which

gives the coefficient of elastic deformability of shallow

foundation geomaterial caused by the load applied on the

considered shallow foundations. The slopes of qa and Vs plots

reflecting the impulse/driving force producing the

deformability of a layers per cubic meter of the foundation

layers is about 0.5 kNs·m−3. From Equations (11 and 12), layers

near surface are more relatively susceptible to deformation than

sublayers based on the magnitudes of qall and shear modulus

G which is plotted against Vs for cohesive and cohesionless

soils as shown in Figures (7 and 8 respectively). As it increases,

the degree of elastic deformation decreases. Although

consolidation of subsurface increases with depth due to

compaction, other tectonically induced secondary structures

like divide, fault lineament and fold within the sedimentary

facies could cause voids in the subsurface thereby leading to

elastic deformation of subsurface.

The layers also show polynomial relationships between qa and

G as shown in Figures (7 and 8) for cohesive and cohesioless

soils respectively. The unit weight of the soil layer also

determines the shear modulus and S-wave velocity in Equation

(1) constitutes the significant variation noticed in layers in the

relation between allowable bearing capacity qa and shear

modulus G which is given by Equations (13 and 14):

For Cohesive Soils qall (kN/m2) =(-4E-06G2 + 0.0061G + 0.4843)×102

(13)

For Cohesionless Soils qall (kN/m2) = (-1E-06G2 + 0.0043G + 0.6675)×102

(14)

The highest value of qall for sublayers is seen on north zone and

reduces through middle and south of Iraq. This trend shows that

low allowable bearing capacity is associated with zones that are

highly undrained with water while the high bearing capacity is

associated with zones that are unsaturated with water. The

appeared transition in magnitude of allowable bearing capacity

toward high value with depth is due to cementation/compaction

which increases with depth.

The results show that the higher value of allowable bearing

capacity in the study areas is obtained in North of Iraq (i.e., N1)

with a value of about 408 kN/m2 and the lowest is at Middle

and South regions (i.e., M10 and S10 respectively) with avalue

of about 50 kN/m2. According to the depths of investigation and

soil descriptions shown in Table (2), three layers with

approximate depths can be considered for investigation, layer

one extends to about 6m from the ground surface, while layer

two extends for a depth 6m to 10m and third one for depth

between 10m to 15m. qall value has an average value of about

142 kN/m2 for layer one, while the average bearing capacity for

layer two is about 176 kN/m2and about 162 kN/m2 for layer

three. With respect to cohesive and non-cohesive soils, the

results of the minimum, maximum and average values of shear

modulus, G, and allowable bearing capacity, qall appears for the

layers to a depth of about 15m from ground surface in the study

areas are as shown in Table (4).

Table 3: Allowable bearing capacity for different soil descriptions.

Soil type Vp -range (m/s) Vs -range

(m/s)

qall ×102

(kN/ m2)

Rock Fragment of Limestone with Silty Sand to Gravel with

Sand or Gravel with Silt and Sand

Silty Sand (Loose)

Silty Sand (Medium)

Silty Sand (Dense)

Gypseous Sand to Silty Sand

Clay (Very Soft to Soft)

Clay (Medium)

Clay (Stiff)

Clay (Very Stiff to Hard)

714-2500

334-909

450-1191

1025-1733

803-1811

294-550

377-820

381-1076

675-1541

292-733

103-243

183-507

279-659

268-627

102-153

131-265

198-398

248-459

1.34-4.08

0.5-1.26

0.84-2.65

1.33-3.23

1.28-2.96

0.5-0.88

0.59-1.33

0.97-2.02

1.18-2.18



1086

Table 4: Shear modulus and allowable bearing capacity for different depths in cohesive and cohesionless soils.

Soil type

Depth

Approx.

(m)

G×103 –value

(kN/m2)

qall×102-value

(kN/m2)

Min. Avg. Max. Min. Avg. Max.

Cohesive

soil

0-6 21.24 105.5 374.17 0.45 1.06 1.96

6-10 83.77 206 413.75 1.03 1.54 2.45

10-15 21.24 207.6 374.17 0.51 1.47 2.18

Cohesionless soil 0-6 44.25 387.76 1354.1 0.7 1.78 4.08

6-10 57.49 693.8 4142.8 0.78 1.97 3.57

10-15 21.23 464.1 3370 0.5 1.76 3.33

Figure 3: Ultimate bearing capacity against shear wave velocity for cohesive soils.

0

5

10

15

20

25

30

0 50 100 150 200 250 300 350 400 450 500

qult(×

10

2 kP

a)

Vs(m/sec)

conventional method [18]

seismic method [17]



1087

Figure 4: Allowable bearing capacity against shear wave velocity for cohesive soils.

Figure 5: Ultimate bearing capacity against shear wave velocity for cohesionless soils.

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

0 50 100 150 200 250 300 350 400 450 500

qal

l(×

10

2kP

a)

Vs (m/sec)

seismic method-n=4 [17]

conventional method-n=3 [18]


0

10

20

30

40

50

60

70

0 100 200 300 400 500 600 700 800 900

Vs (m/sec)

seismic method [17]

conventional method [18]

qal

l(×

10

2kP

a)



1088

Figure 6: Allowable bearing capacity against shear wave velocity for cohesionless soils.

Figure 7: Allowable bearing capacity against shear modulus for cohesive soils.

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250 300 350 400 450

qal

l(×

10

2kN

/m2)

G(×103 kPa)

0

5

10

15

20

25

30

0 100 200 300 400 500 600 700 800 900

qall

(×10

2kP

a)

Vs (m/sec)

2 .2 2

4 .0 8

5 .4 5

seismic method-n=4 [17]





1089

Figure 8: Allowable bearing capacity against shear modulus for cohesionless soils.

Evaluation of the Soil Parameters

This study aimed also at obtaining model equations from the

correlations of the shear wave velocities and the different

geotechnical parameters studied. This was to obtain direct

relationships between the S-wave velocity and the geotechnical

parameters. These equations can be used for a quick evaluation

and inexpensive estimation of the various soil parameters.

The graphs of the parameters were plotted against the shear

wave velocities. Also, the relations and correlations have been

investigated between seismic velocities and geotechnical

parameters using the best fit curve. The relations give obvious

variations in the geotechnical properties affecting the velocities

differently in different parts of the velocity ranges.

The graphs of modulus of elasticity, E, bulk modulus, K, and

subgrade modulus, ks, against the S-wave velocity (Figures 9,

11 and 13 respectively) gave the empirical equations defined in

Equations (15, 16 and 17) for cohesive soils. And the plots of

modulus of elasticity, E, bulk modulus, K, and subgrade

modulus, ks, against the S-wave velocity (Figures 10, 12 and

14 respectively) gave the empirical equations defined in

Equations (18, 19 and 20) for cohesionless soils. The equations

shows polynomial relationships between E with Vs and

exponential relationship between K and Vs and linear

relationship between ks with Vs. The minimum, maximum, and

average values of modulus of elasticity, E, bulk modulus, K,

and subgrade modulus, ks for the cohesive and cohesionless

soils estimated to a depth of about 15m from ground surface in

the study areas are given in Table (4).

This result shows that the lower layers are more compressed

than the first layer. This may be as a result of the geologic

formation of these layers, their level of saturation and the level

of cementation of the geomaterial. It was also indicated that the

Young modulus of the subsurface increased in direct proportion

with the seismic wave velocity and the two parameters

generally increased with depth. This also shows that the second

layer has more strength than the other layers. The results also

shows that the first layer would deform more easily under shear

stress than the lower layers. The bulk modulus results further

confirmed that the second geologic layer to be more competent

than the first layer. The subgrade modulus ranges also reveals

that the second geologic layer is more competent than the first

layer.

For Cohesive Soils

E (kN/m2) = (0.0047Vs2 + 0.5284Vs-47.13) ×103 (15)

K (kN/m2) = (0.1566e0.0074Vs) ×106 (16)

ks (N/m2.s)= (0.0008Vs - 0.0119) ×108 (17)

For Cohesionless Soils

E (kN/m2) = (0.0047 Vs2 – 0.4619Vs

-50.866) ×103 (18)

K (kN/m2) = (0.2789e0.005Vs) ×106 (19)

ks (N/m2.s) = (0.0008Vs - 0.0002) ×108 (20)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 200 400 600 800 1000 1200 1400 1600

qal

l(×

10

2kN

/m2 )

G(×103 kPa)



1090

Table 4: Soil parameters for different depths in cohesive and cohesionless soils in the study areas.

Soil type

Depth

Approx.

(m)

E×103 -value

(kN/m2)

K×106-value

(kN/m2)

ks ×108-value

(N/m2.s)

Min. Avg. Max. Min. Avg. Max. Min. Avg. Max.

Cohesive

soil

0-6 57.9 304.14 835.5 0.13 1.34 6.62 0.072 0.169 0.314

6-10 239.1 592.7 1204.8 0.55 1.88 4.56 0.165 0.247 0.392

10-15 62.57 588 1082.8 1.58 1.58 3.41 0.082 0.236 0.35

Cohesionless

soil

0-6 124.2 1057.6 3642.6 0.21 2.28 5.14 0.113 0.303 0.65

6-10 167.5 1926.5 11343 0.29 3.64 14.43 0.124 0.39 1.191

10-15 61.8 1313 9397 0.23 3.43 14.62 0.08 0.316 0.953

Figure 9: Young’s modulus against shear wave velocity for cohesive soils.

0

200

400

600

800

1000

1200

1400

0 50 100 150 200 250 300 350 400 450 500

E(×

10

3kP

a)

Vs(m/sec)



1091

Figure 10: Young’s modulus against shear wave velocity for cohesionless soils.

Figure 11: Bulk modulus against shear wave velocity for cohesive soils.

0

500

1000

1500

2000

2500

3000

3500

4000

0 100 200 300 400 500 600 700 800 900

E(×

10

3kP

a)

Vs(m/sec)

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300 350 400 450 500

K(×

10

6kP

a)

Vs(m/sec)



1092

Figure 12: Bulk modulus against shear wave velocity for cohesionless soils.

Figure 13: Subgrade modulus against shear wave velocity for cohesive soils.

0

5

10

15

20

25

30

35

40

0 100 200 300 400 500 600 700 800 900

K(×

10

6kP

a)

Vs(m/sec)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 50 100 150 200 250 300 350 400 450 500

k s(×

10

8N

/m2.s

ec)

Vs(m/sec)



1093

Figure 14: Subgrade modulus against shear wave velocity for cohesionless soils.

CONCLUSION

The conclusions that can be drawn from this study can be

summarized as follows:

1. Ranges for values of seismic wave velocities and

allowable bearing capacity for different types of soil

with various description are presented, extending the

knowledge for the limit of theses values. Also the

allowable bearing capacity values obtained from hard

through loose soils were in agreement with the

building codes and references values.

2. Correlations between seismic velocity Vs and

allowable bearing capacity has been obtained. This

relationship show direct proportionalities between Vs

with qall. The results show that the range of bearing

capacity for the study area was between 50 and 408

kN/m2, being highest at north regions and reduces

through middle and south regions of Iraq.

3. The cross and down hole tests results revealed three

geologic layers with the second layer being more

competent. qall value has an average value of about

142 kN/m2 for layer one, while the average bearing

capacity for layer two is about 176 kN/m2and about

162 kN/m2 for layer three.

4. As the bearing capacity is a mechanism where large

shear strains develop and the measured shear wave

velocity is based on very small strains, thus the

bearing capacity estimated from the shear wave

velocity may be used to check the values calculated by

other means.

5. The empirical equations obtained can be used to

evaluate and predict the geotechnical parameters of

the study area studied.

6. Empirical expressions estimated for the allowable

bearing capacity using shear wave velocities

measured at low shear strains, is appropriate to

produce reliable results for a wide range of soil

conditions.

7. Allowable bearing capacity increases with increase in

shear modulus enhanced by high shear wave velocity.

For cohesive and cohesionless soils it was indicated

that up to a shear wave velocity of 300 m/s and 400

m/s respectively, the shear wave velocity may predicts

the bearing capacity relatively well.

8. Using the empirical formulations generated from the

sites data, surface layer has been found to show lower

bearing capacity than layers two and three based on

the coefficients of elastic deformability of shallow

foundation realized from the plots of qall against G.

The layers also show relationships of seconed order

between qa and G.

9. Correlations between seismic velocity Vs and

geotechnical properties have been derived. These

relations show polynomial relationships between E

with Vs and exponential relationship between K and

Vs and linear relationship between ks with Vs.

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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 100 200 300 400 500 600 700 800 900

k s(×

10

8N

/m2.s

ec)

Vs(m/sec)



1094

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http://dx.doi.org/10.2478/s11600-008-0077-z

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