Research ArticleGrouting Reinforcement of Large Building Foundation over OldGob Areas A Case Study in Huaibei Mining Area China

Wenyan Guo12 Shiqi Liu 13 Bingnan Hu2 Yanchun Xu1 and Yaqi Luo1

1School of Resources and Safety Engineering China University of Mining and Technology Beijing 100083 China2National Key Lab of Coal Resources High Efficient Mining and Clean Utilization China Coal Research Institute Beijing 100013China3Hebei State Key Laboratory of Mine Disaster Prevention North China Institute of Science and Technology Beijing 101601 China

Correspondence should be addressed to Shiqi Liu liushiqi0217qqcom

Received 16 June 2018 Revised 12 September 2018 Accepted 18 October 2018 Published 3 December 2018

Academic Editor Robert Cerny

Copyright copy 2018Wenyan Guo 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

ere are more than 14000 square kilometers of mining subsidence areas in China most of which have been reclaimed for theconstruction of new buildings In the past few special measures were required for the foundations of small buildings above old gobareas But a plan was created to construct a large office building 100m in length 90m in width and 100m in height above old gobareas in the Huaibei subsidence area However the results of exploration borehole data and borehole TV observation indicateda broken bedrock stratum and developmental fractures above the old gob areas and thus the space stabilities of the buildingfoundation were poor erefore grouting reinforcement measure was adopted for the old gob and foundation areas And thegrouting effect was examined using borehole TV observation and the water injection test where the detection results of boreholes TVobservation showed that the filling ratio of the stratum fracture was over 85 and the stability of the foundation was obviouslyenhanced In addition wemonitored the settlement of the foundation continuously for 930 dayse results show that themaximumcumulative subsidence was 153mm and the maximum slope was 005mmm which verifies that grouting reinforcement is feasiblein terms of the safety of large buildings constructed over old gob areas using bedrock stratum grouting in theHuaibei subsidence area

1 Introduction

Owing to the large-scale and high-intensity mining of coalresources over the past several decades a large number ofmining subsidence areas have been created According toincomplete statistics there are more than 14000 km2 ofmining subsidence areas in China accounting for 15permil ofthe total national land area With diminishing coal resourcesand an acceleration of the nationrsquos economic trans-formation land resources have become increasingly scarcein mining areas so it is vital to reuse land in subsidence areas[1 2] Some examples of such use include land reclamationand ecological reconstruction in the Nanpiao mining areaand a pond aquaculture in the Yongcheng mining areaHowever most of these land areas have been reused for theconstruction of new buildings Damage to buildings con-structed above old gob areas has also occurred because thedeformation and instability of the rock layers above the gobs

caused the new building to settle partially crack tilt andcollapse [3] e higher the building height is the easier it isto be destroyed [4] Bruhm [5] Healy and Head [6] Yanget al [7] Teng et al [8] and Guo and Wang [9] hadresearched the stability of old gobs and building foundationand proposed the deformation and failure laws Somestudies have found that the instability and residual de-formation of the old gob areas are the main factors con-tributing to this damage

Many studies have shown that there are three distinctzones (caved fracture and continuous deformation zones)from the coal seam to the ground created by the movementof the overlying strata in longwall mining (Figure 1)Turchaninoy and Iofis [10] and Palchik [11] have put for-ward the ideas that the caved zone is highly fragmentedrocks from the overlying rock layers fall to the coal floorand break into various irregular shapes and some unfilledcavities exist next to the coal wall and mining roadway

HindawiAdvances in Civil EngineeringVolume 2018 Article ID 8738752 11 pageshttpsdoiorg10115520188738752

Above the caved zone is the fracture zone and Karmis et al[12] and Whittaker and Reddish [13] have concluded thatthe separation of the rock layers is severe the vertical andhorizontal fractures are developed and the rock layers arebroken into blocks in the lower and middle parts of thefracture zone but in the upper part the rock layers arerelatively complete and horizontal fractures are mainlyfound along the interface of the rock layer Jung et al [14]and Gueguen et al [15] have found that the surface developscontinuous settlement and residual deformation aftermining has been stopped for five to seven years and thatresidual rock cavities bed separation and fractures are stillpresent even after a long period of slow compaction Tengand Zhang [16] have hypothesized that when these cavitiesbed separation and fractures in the caved and fracture zonesare influenced by the additional stress caused by a buildingthis stress accelerates the compression and movement of theunstable bedrock thereby creating an uneven settlementtilting or even a collapse of the new building foundation

Huaibei Mining Co operates a large-scale coal pro-duction area and it has created a wide spread of subsidenceareas Huaibei Mining Co intended to build an officebuilding over old gob areas at the Xiangchen Mine In thepast most of the new buildings over old gob areas weresmall low-rise buildings with small foundation acreage andbuilding loads so special reinforcement measures forfoundation and old gob areas were not required Howeverthe planned office building by Huaibei Mining Co wasunique because it was a large high-rise building edesigned size of the office building was 100m times 90m times

100m and the acreage of the foundation would span threeold gob areas erefore the foundation might easily createan uneven settlement and deformation Moreover the gobsbelow the ground were buried shallowly from 90 to 115mand the load given by the office building was large and thusthe influence of additional stress due to the buildingtransferred into the caved and fracture zones causing anadverse impact on the building foundation According to thepreliminary analysis there was a high risk to construct theoffice building directly above the old gob areas In this casethe grouting reinforcement measure was put forward toreinforce the building foundation

Currently some scholars have suggested several evalu-ation methods for the stability of building foundations overold gob areas such as numerical and similarity simulations[17 18] and nonlinear evaluations [19 20] However many

of these evaluation methods are based on statistical studiesempirical analyses or simulation studies Related fieldstudies have been insufficient in evaluation In this paperbased on borehole exploration borehole TV imaging testgeophysical prospecting and field monitoring the stabilitiesof the old gob areas and the building foundation and theeffect of grouting reinforcement were studied and analyzedis paper strengthens the theoretical study on the stabilityof old gob areas and building foundations and accumulatesthe field experience of grouting reinforcement of old gobareas so it provides a reference for the construction ofsimilar buildings in mining subsidence areas

2 Exploration of the Gobs and StabilityEvaluation of the Foundation

21 Study Area Description e large high-rise officebuilding (100m times 90m times 100m) was built over the old gobs atthe Xiangchen Mine and the range of the construction sitewas delimited to about 400m times 380m ere are seven oldgobs (marked as 571 through 577 gobs) under the con-struction site buried at a depth of 90 to 115m Only No 5 coalseam had been mined using strike longwall blast mining ata mining height of 25m and themining had been stopped formore than 30 years e relative positions of the officebuilding construction site and old gobs are shown in Figure 2e average thickness of the bedrock above the No 5 coalseam is 30m and the lithology is mainly mudstone and thicksandstone e Quaternary strata which are mainly sand andclay layers are above the bedrock with an average thickness of70me types of underground water from ground to the No5 coal seam are quaternary sand layer pore water weatheredzone fissure water and sandstone fissure water e quater-nary sand layer aquifer could not generate a hydraulic con-nection with the other aquifers below owing to the presence ofa clay layer with good water tightness Weathered zone fissurewater and sandstone fissure water are the main water sourcesof the No 5 coal seam the water inflow of the sandstonefissure aquifer based on a pumping test was 00035 Lsmiddotm to00304 Lsmiddotm and thus water was not abundant

22 Borehole Exploration Seven exploration boreholes(marked as K1 through K7) were constructed and the po-sitions are shown in Figure 2 K1 K2 K3 and K6 boreholeswere located at the center of the gobs K4 and K5 boreholeswere located at the edge of the gobs and K7 borehole waslocated above the roadway In the process of drilling bore-holes K1 K2 K3 and K6 boreholes incurred wind inhalationin the caved zone deducing that the rock mass was frag-mented and accumulated in the center of the gobs K4 K5and K7 boreholes incurred drill felling deducing that therewere unfilled cavities near the coal pillars ormining roadwayse office building foundation would make uneven de-formation easily when it spanned old gobs and coal pillars

221 Stratigraphic Characteristics of Borehole CoreAccording to the data on the exploration boreholes theQuaternary strata were exposed from 660 to 739m with

III

II

I

Vertical fractures

Bed separation

Rock blocksCavities

Figure 1 Zones of overlying strata movement by longwall miningI caved zone II fracture zone III continuous deformation zone

2 Advances in Civil Engineering

an average thickness of 70m e burial depth of thebedrock was from 70 to 110m and the lithology from thebedrock surface to the roof of the No 5 coal seam wasweathered mudstone siltstone sandstone mudstonemagmatic rock and mudstone e bedrock was dividedinto three sections

e upper section was between 70 and 85m in depthHere the rock mass was more complete fractures were lessdeveloped and the lithology was mainly weathered mud-stone and siltstone But the coring rate was low so completecores could not be obtained except from the K4 boreholeAccording to the core samples taken from the K4 borehole atdepths of between 793 and 883m (Figure 3) the mudstone(circled in red) was much broken

e middle section was located at a depth of 85 to 97mHere fractures and caves were more developed the rock masswas incomplete and broken and the lithology was mainlysandstone and magmatic rocks but the coring rate was lowAccording to the core samples from the K4 borehole ata depth of 883 to 937m (Figure 4) the sandstone broke intoblocks

e bottom section was between 97 and 110m in depthHere the rockmass was fragmented a variety of rockmasseshad accumulated the lithology was mixed more cavitieswere present and drill felling or wind inhalation occurrede bottom section was unable to obtain a relatively com-plete rock core and thus it was deduced that it was a cavedzone or uncompact roadway

According to rock mechanics test results of the rocksamples (Table 1 where Rc is the uniaxial compressivestrength and Rt is the uniaxial tensile strength) thecompressive strength of the mudstone and sandstone wasless than 20MPa indicating that the compressive capacityof the bedrock was weak Moreover the mudstone wassoftened and muddied quickly when touched by water

us the bedrock would incur large deformations andsedimentation when under a high load given by thebuilding

222 Borehole TV Imaging Test A borehole TV imaging testwas used to image the entire hole wall by observing theexploration boreholes and some of the observed results arerecorded in Table 2 It can be seen that the fractures haddeveloped rock was broken from 83 to 94m in depth androck had collapsed from 94 to 102m Parts of images of theK6 borehole are shown in Figure 5 and it can be seen thatvertical fractures developed from 891 to 911m and rockcollapsed from 986m when close to the gob erefore the

From 793m to 883m

Figure 3 Characteristics of the borehole core in the upper section

From 883m to 937m

Figure 4 Characteristics of the borehole core in themiddle section

Table 1 Test results of the mechanical properties of the rocksamples

Rock samples Rc (MPa) Rt (MPa)K4 mudstone 1 249 mdashK4 sandstone 1 1913 mdash

K6 mudstone

1 065 (drying) mdash2 110 (drying) mdash3 049 (drying) mdash

Average value 075 mdashK7 mudstone 1 1926 048

K7 igneous

1 4693 mdash2 5418 mdash3 3309 mdash

Average value 4443 mdash

574 gob

572 gob

576 gob 577 gob

575 gob

573 gob571 gob

K1

K3 K6

K7K2

K5

K4

1080

1160

1240

1320

Exploratory boreholeGobs boundary

Transient electromagnetic line

Construction site boundaryOffice building boundary

Figure 2 Location of office building construction site and oldgobs

Advances in Civil Engineering 3

residual rock cavities and fractures were still present in theold gob areas and there was a high possibility for the brokenbedrock to lose their stability when under the large loadgiven by the office building

223 Height Observation of Caved and Fracture Zonese caved and fracture zones were unstable areas above theold gob areas and the range of these areas can be calculatedby observing the leakage of flushing fluid through drillingFlushing fluid was continuously poured into the borehole asthe amount of leakage increased in the cavities and fracturesthe location where the leakage increased significantly wasmarked as the top of the fracture zone and the locationwhere the flushing fluid leaked overall or drill felling fre-quently occurred was marked as the top of the caved zoneAccording to the observations of the exploration boreholesand data (Table 3) taking the maximum value the heights ofthe caved zone (Hk for short) and fracture zone (Hli forshort) were 214 and 64m respectively

23 Transient Electromagnetic Geophysical Exploration

231 Exploration Arrangement Transient ElectromagneticGeophysical Exploration (GDP-32II) was used to detect thestratigraphic conditions below the construction site Foursurvey lines were projected along the north-south directionand the 1080 1160 1240 and 1320 numbered lines were inturn projected from west to east with an adjacent spacing of80m and an adjacent measuring point spacing of 15m elocations of the survey lines are shown in Figure 2

232 Exploration Results A profile map of the apparentresistivity contours of the survey lines is shown in Figure 6

Table 2 Observation results of exploration borehole based on the TV imaging test

Borehole no Observation results using the borehole TV imaging testK1 Fractures developed at 780m depth rock collapsed from 923 to 973mK2 Fractures developed from 88 to 97m rock collapsed from 97 to 99mK3 Fractures developed rock broke from 902 to 982m and collapsed from 982 to 1022mK5 Fractures developed rock broke from 838 to 936m and collapsed from 936 to 96mK6 Fractures developed rock broke from 891 to 986m and collapsed from 986 to 1045mK7 Rock seriously broke the hole wall collapsed at 102m depth

Depth(m) N

891

896

901 911 991

906 986

901 981

E S W N N E S W N N E S W N

Figure 5 Parts of observed images of the K6 borehole

Table 3 Observation results of the Hk and Hli of the boreholes

Borehole no K1 K2 K3 K4 K5 K6 K7Hk (m) 50 30 40 64 34 36 44Hli (m) 210 135 160 214 122 116 138

4 Advances in Civil Engineering

According to the analysis in areas where the vertical depth isless than 80m the apparent resistivity value was between100 and 450Ωmiddotm and the areas were considered to bea relatively high resistance zone and speculated to be madeup of a quaternary loose layer However these areaswere transverse in scale from 100 to 260m (in Figures 6(a)and 6(b)) or 100 to 390m (in Figures 6(c) and 6(d)) and ata vertical depth of 80 to 110m the apparent resistivity valuewas between 20 and 80Ωmiddotm and the area was thereforeconsidered a relatively low resistance zone Given that therewere more residual cavities and fractures in the caved orfracture zone the sandstone water may be connected andhydrops may have formed in the gob thus causing lowresistance erefore the relatively low resistance zone wasspeculated to be a caved or fracture zone Based on theexploration results the scope of the caved and fracturezones was large and the apparent resistivity was low whichindicates that the bedrock was broken and that fractureshad developed above the old gobs hindering the stability ofthe gobs

24 Stability Evaluation of the Building FoundationDisturbance caused by the additional stress (caused bya building) on the unstable bedrock in old gob areas is one ofthe important reasons for damage to a foundation Assumethat the surface of the building foundation is a regularrectangle and the origin of the coordinate system is themidpoint of the top surface of the foundation According tothe superposition principle and integral method the addi-tional stresses (σaz for short) of the midpoint at differentdepths (z) under a uniform load are calculated using thefollowing equation [21]

⎧⎨

⎩σaz 4p

2π1113890arctg

m

n1 + n2 + m2

radic +mn

1 + n2 + m2

radic

middot1

n2 + m2 +1

1 + n21113874 11138751113891 4Ksp m l

b n

z

b

⎫⎬

⎭

(1)

where l is one-half of the long side of the rectangle b is one-half of the short side p is the vertical load and Ks is theadditional stress coefficient taken from the appendix k of thecode

Also the regarded depth is where the additional stress is10 of the gravity stress (σz for short) of the soil or rockunder the foundation as the depth affected by the load givenby the building (hz for short which the top is the ground)e office building has a twin tower structure where eachsingle building is 854m long (so l equals 427m) and 386mwide (so b equals 193m) In addition the building is 10min depth (below the ground) erefore the depth of thefoundation surface is 10m (thus hz equals z plus 10) etotal load of all 19 floors is 675 kPa the Quaternary strata are70m thick with the average bulk density of 20 kNm3 andthe average bulk density of the bedrock is 25 kNm3 So thevalue of σz can be calculated using Formula (2) and thecalculated results of σaz σz and hz are shown in Table 4

σz

20 kNm3( 1113857 times z when zle 60m

20 kNm3( 1113857 times 60

+25 kNm3( 1113857 times(zminus 60) when zgt 60m

⎧⎪⎪⎪⎨

⎪⎪⎪⎩

(2)

According to the observed and calculated results inTables 3 and 4 the height of the fracture zone (Hli) was214m and the depth affected by the load (hz) was 82meshallowest depth of the No 5 coal seam (Hs for short) was96m which was less than the sum of 214m and 82m Asshown in Figure 7 the areas affected by the load overlappedwith the fracture zone us the additional stress caused bythe office building would influence the stability of thefracture zone and might cause a large uneven settlement anddeformation of the foundation

3 Grouting Reinforcement

Owing to the instability of the building foundation therewas an extremely high risk to construct the office buildingdirectly above the old gob areas and thus the groutingreinforcement measures were needed e grouting re-inforcement of the old gob areas can effectively fill thecavities and fractures in the caved and fracture zones withthe grouting slurry by cementing the cavities or fractureswith the surrounding rock into a whole thereby improvingthe carrying capacity and stability of the coal and rock andreducing the deformation of the gob areas and the buildingfoundation In this way the safety and stability of thebuildings above the old gob areas was ensured

e scope of the grouting area delimited by the ver-tical section method [22] was larger than the building(Figure 8(a)) e movement angle of the Quaternary strata(φ) and the strike movement angle of the bedrock (δ) wereselected according to the previous statistics data and thegrouting scope along the strike was shown in the I-I strikeprofile (Figure 8(b)) e same method was adoptedalong the dip which was not shown here Eighteen groutingboreholes (borehole Z1 through Z18) were designed(Figure 8(a)) and three grouting boreholes (borehole Z3Z6 and Z7) made use of the previous exploration boreholes(boreholes K3 K6 and K7)

e cavities fractures and separation of the bedrock inthe caved and fracture zones were the main grouting areasaccording to the observed results of the exploration bore-holes and the minimum burial depth of the top of thefracture zone was 76mMoreover the floor failure caused bymining was considered and thus the range of the groutingsegment was designed to be from the 75m under the groundsurface to 3m below the floor of the No 5 coal seam emaximum grouting pressure was set to 15MPa and theinterval of the two adjacent grouting boreholes was between30 and 50m Slag cement and fly ash were used as the mainsolid grouting materials the mass ratio of cement to fly ashwas designed to be between 1 4 and 1 9 and the water-solidratio of the grouting slurry was 08 1 or 06 1 Groutingbegan on January 14 2011 and ended on March 27 2011including drilling of the 18 grouting boreholes About

Advances in Civil Engineering 5

48624 tons of cement and 266027 tons of fly ash wereconsumed Detailed information regarding the groutingtime grouting amount and reason for stopping the groutingof 11 boreholes are provided in Table 5 It can be seen that allthe grouting amounts of boreholes Z3 Z4 Z7 Z14 and Z17were more than 2000 tons and the grouting time was longerthan two weeks Moreover the location of those boreholes

was close to the coal pillars or roadways indicating that thescope of the uncompacted areas and the slurry-filling areasbelow were great Emission of slurry on the ground occurredat seven boreholes and the field inspection indicated that theuncompacted areas in the old gob areas had been filled withthe slurry effectively

4 Results and Discussion

41 Detection and Analysis of the Grouting Effect

411 Drilling of Detection Boreholes Four detection bore-holes (marked J1 through J4 shown in Figure 8(a)) wereconstructed after grouting Compared with the surroundingexploration boreholes (K3 K6 and K7 boreholes) during theprocess of drilling no drill felling or wind inhalation oc-curred and the J1 and J4 boreholes no longer incurreda water leakage (Table 6) It can be concluded that thegrouting had a favorable effect on the fracture filling

412 Borehole TV Imaging Test A borehole TV imaging testwas used to image the full borehole wall to observe thefractures in the bedrock of four detection boreholes Becausethe rock had joints and fractures the surface filled withslurry was smoother than the surface of the rock In additionthe color of the slurry was grayish white and the rock waslight grayish black but the colors of the unfilled fracturesand cavities were black According to the identification andprocessing of the images the results of filling rates of de-tection boreholes were greater than 85 And TV images ofthe J1 borehole are shown in Figure 9 the areas filled in withslurry were circled with the green lines and the unfilled areas

100 120 140 160 180 200 220 240 260 280 300 320

100 120 140 160 180 200 220 240 260 280 300 320

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash2020

015

010

0

30100

100

250

60405080150 350200

400450

40

200250

250

200

150

100

506080

300

8030 40 6050

20

(a)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

150 200

250

300

450250200

300350

400

40 80 6050

100 150

40

10080

60

5040

(b)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

5040

3025

020

0

30405060

1001508060 50

250200 400350

300 250

20015010080605040

40

(c)

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

10

60 2030 40 4040

200

350300250200150100806050

50

400 450

203040

40

350300

250200150100806050

250

5080(d)

Figure 6 Profile map of apparent resistivity contours of Transient Electromagnetic Geophysical Exploration (a) 1080 survey line (b) 1160survey line (c) 1240 survey line (d) 1320 survey line

Table 4 Depth affected by the load

z(m) n

p

(kPa) Ksσaz

(kPa)σz

(kPa)10 σz(kPa)

hz(m)

0 0 675 025 675 0 0 1025 130 675 0176 4509 500 50 3550 259 675 0092 2484 1000 100 6070 363 675 0058 1566 1425 1425 8072 373 675 0054 1458 1500 150 82

No 5 coal seam

Ground

Building

Areas affectedby the load(σaz gt 01σz)

Foundation surface

Additional stress(σaz = 01σz)

Hli = 214m

h z=

82m

Old gob areas

Hs=

96m

Figure 7 Relationship between the areas affected by the load andthe fractured zone

6 Advances in Civil Engineering

were circled with the red lines It can be seen that most of thecavities and fractures were filled with slurry and the closer tothe gobs the better of the grouting effect Comparing theafter grouting images results with the before grouting imagesresults (Table 2 and Figure 5) it was believed that themechanical properties of rock mass were strengthened andthe grouting project was successful

413 Water Injection Test Water injection tests were alsoconducted on a water column in the detection boreholesand the permeable rates of boreholes J1 J2 and J4 were0072 0992 and 0378 Lu respectively e permeable rateswere less than 1 Lu so the type was micropermeable andthus the cavities and rock fractures were filled in with the

slurry effectively after groutinge flushing fluid showed noor slow loss during drilling and thus the hydraulic link ofthe surrounding bedrock was poor In addition the bedrockwas able to maintain a certain water level when the waterlevel around it changed thereby avoiding the influence ofwater on the mudstone layer

42 Analysis of Other Factors to the Stability of the Foundation

421 Quaternary Sand Aquifer Observation from the ex-ploration boreholes in the old gob areas indicated that thecurrent groundwater level in the construction site was below100m No hydraulic connection existed between the Qua-ternary aquifer and the gobs and the change of the water

Table 5 Parameters of grouting boreholes

Drillingno

Grouting time Groutingamount Reason for

stopping groutingStarting Ending Cement

(t)Fly

ash (t)

Z3 Jan 14 Jan 29 6074 26352 Emitting of slurryat ground

Z6 Jan 14 Jan 15 340 1757 Emitting of slurryat ground

Z7 Jan 15 Feb 20 10685 42163 Emitting of slurryat ground

Z5 Jan 18 Jan 26 3854 18739 Emitting of slurryat ground

Z14 Feb 6 Feb 21 4998 25181 Reachinggrouting pressure

Z12 Feb 18 Feb 19 192 878 Emitting of slurryat ground

Z17 Feb 21 Mar27 8296 38544 Emitting of slurry

at ground

Z13 Feb 27 Mar 8 1390 7788 Reachinggrouting pressure

Z16 Mar 8 Mar27 1906 11110 mdash

Z4 Mar 10 Mar27 3963 25824 Emitting of slurry

at ground

Z8 Mar 22 Mar27 1055 9792 mdash

Table 6 Characteristics of the boreholes before and after grouting

Time Borehole Leakage observation Drillfelling

Windinhalation

Beforegrouting

K3995m to end all lostleakage more than

15m3hNo Yes

K61015m to end all lostleakage more than

15m3hNo Yes

K7899m to end all lostleakage more than

15m3hYes Yes

Aftergrouting

J1 No leaking No No

J2 899m to end a little lostleakage only 054m3h No No

J4 No leaking No No

A BMI N I

574 gob

572 gob

576 gob

Z15

Z16

Z17

Z1Z2

Z3(K3)

Z4Z5

Z6 (K6)

Z7(K7)

Z8

Z9Z10

Z11

Z12

Z13Z14

J4(Z18)

J1J2

J3

Detecting borehole

Office building boundaryGrouting range boundary Strike profile line

Grouting borehole

(a)

Q

φ

δ δ

φ

Building

Old gob areas

A BM N

Scope of the grouting treatment

hh j

I-I profile

(b)

Figure 8 (a) Grouting scope design and grouting boreholes ar-rangement (b) grouting scope of the I-I profile φ movement angleof Quaternary strata δ strike movement angle of bedrock QQuaternary strata h thickness of Quaternary strata hj thickness ofbedrock

Advances in Civil Engineering 7

level in the Quaternary sand aquifer was small ereforethe settlement of the soil layer caused by aquifer consoli-dation was small and the influence of the aquifer on thefoundation settlement was small

422 Pile Foundation Considering the heavy load given bythe building reinforcement measure of constructing pilefoundation was taken in addition to grouting reinforcemente depth of the pile foundation was 50m and the pilefoundation had good stability and large bearing capacitywhich reduced the settlement caused by compression of theQuaternary sand and soil layere strength of the backfilledrock mass and the backfilling material in the gob areasendured the additional load given by the pile foundation sothe stability of the gob areas was achieved

423 Residual Deformation of the Office BuildingFoundation Combined with the grouting effect the geo-logical conditions the building load and past experiencesan integral probability method [22] was used to calculate theresidual deformation and subsidence of the surface aftergrouting and the relevant parameters are shown in Table 7e contour line of the residual surface subsidence and theslope in the area where the office building was located areshown in Figure 10 Results showed that the maximumsurface subsidence value was 58mm and the maximumslope was 042mmm both of which are less than thepermissible subsoil deformation of a high-rise building (thepermissible subsidence was 200mm and the permissible

slope was 2mmm as taken from [21]) us constructionof the office building was made feasible

Owing to the detection and analysis of the groutingeffect the cavities and fractures of the bedrock were betterfilled and the force of the rock was changed from two-dimensional to three-dimensional which enhanced theoverall strength of the rock mass Meanwhile the stability ofthe foundation was effectively enhanced by constructing pilefoundation Since the residual deformation and subsidenceof the office building after grouting met the design re-quirements it became feasible to construct the officebuilding above the old gob areas

43 Monitoring Subsidence of the Office Building To acquirethe deformation of the office building timely during con-struction the subsidence of the building was monitored byan electronic level e actual boundary location of the officebuilding is shown in Figure 11 and twenty-two monitoringpoints were set in the buildingrsquos walls e monitoring pointnumbers are shown in Figure 11

Depth(m) N

947 973 998

1003978952

957 983 1008

E S W N N E S W N N E S W N

Figure 9 Images of the J1 detection borehole

Table 7 Parameters of surface movement after grouting

Calculated parameters Construction siteSubsidence factor 0025Main effecting angle tangent 16Displacement factor 030Mining affects the propagation angle 85Inflection point offset 0

8 Advances in Civil Engineering

e monitoring period of 930 days (from October 262012 to May 13 2015) was divided into four stages duringwhich 18 times of monitoring were conducted In stage 1(from day 0 to day 60) the building was constructed from 7floors to 17 floors so the load given by the office buildingincreased faster in this stage In stage 2 (from day 60 to day360) the building was capped and the walls were completede load increase in this stage was limited and some of themonitoring points were damaged by the construction Instage 3 (from day 360 to day 720) the whole building wascompleted and the indoor and outdoor renovation wascarried out In stage 4 (from day 720 to day 930) the buildingwas ready for use erefore the load in stage 3 and 4 wasalmost unchanged and stable

Because some of the monitoring points were damagedparts of the monitoring data were missing erefore twelvepoints (W1 W4 W6 W8 W9 W11 E1 E4 E6 E8 E9 andE11 points) were selected because their data were morecomplete and their locations were closer to the junction andmiddle of the boundary and the cumulative subsidence datawere recorded (Figure 12)

From Figure 12 it was found that all the subsidencevalues of the monitoring points increased rapidly in stage 1which might be caused by the increase of the load and therapid compression settlement of the stratum In this stagethe maximum subsidence value of point W9 was 85mmwith a sinking speed of 0142mmday e maximum slopeof points W1 and W2 was 0492mmm In stage 2 thesubsidence values changed irregularly and the subsidencevalues of some monitoring points were even negative in-dicating that the altitude of these monitoring points wereenhanced As all the monitoring points were set in the wallsthis phenomenon might be resulted from the artificialdisturbance to these monitoring points during the con-struction process of the building walls In stages 3 and 4 thesubsidence values were continuously increased but thespeeds were slowed down obviously indicating the slowcompression settlement of the strata under the stable load Inthese two stages the maximum subsidence and sinkingspeed values from point E6 were about 5mm and0009mmday respectively Comparing stage 1 with stages 3and 4 it can be seen that the subsidence values increased

rapidly with increasing load However with the increase ofthe subsidence accumulation and the slowdown of theapplied load the speed of the foundation subsidencedropped Combining Figure 11 with Figure 12 it can beseen that the subsidence values of those points located closeto the center of the old gob areas (eg points E4 and E6)were more than the points near the pillars (eg points W1and E1) In this way uneven settlement was generated andthe maximum difference of the value from points W1 andW4 was 104mm In the whole subsidence period therewas still residual subsidence because of the unfilled frac-tures in the strata Among the 22 monitoring points themaximum cumulative subsidence value was 153mm frompoint E4 and the maximum slope was 0765mmm frompoints W1 and W2 However compared with the per-missible subsoil subsidence (200mm) and permissiblesubsoil slope (2mmm) the maximum subsidence andslope were far less than the permissible values e officebuilding was built successfully after grouting (a photographof building is shown in Figure 13) cracking or otherdamages during construction did not occur us thestability of the foundation was enhanced greatly by the

4543

4147

4951

5355

57

5553

51

5759

Office building

(a)

05

03

010

3

01

01

Office building

(b)

Figure 10 Map of residual surface subsidence and slope contours in the area where the office building was located (a) map of residualsurface subsidence contours unit as mm (b) map of residual slope contours unit as mmm

W6W7 W8 E8 E7

E6

E5

E4

E1E2E13

E11E10

E9W9

W10

W11

W1W2W3

W4

W5

574 gob

572 gob

576 gob

Monitoring points

Figure 11 Location of the building and the monitoring points

Advances in Civil Engineering 9

grouting reinforcement which proved that the groutingreinforcement of the office building can be adopted forother large buildings constructed over old gob areas

5 Conclusions

According to the observed results from borehole explorationand the TV imaging test all 7 exploration boreholes incurredwind inhalation or drill felling e bedrock chosen for thebuilding construction had been broken and serious frac-tures had developed above the old gob areas us thestability of the gob areas was poor

e depth affected by the load (caused by the officebuilding) was 85m and the largest height of the fracturezone induced by mining was 214m And the shallowestburial depth of the No 5 coal seam was 96m and thereforethe fracture zone overlapped with the areas affected by theload of which the stability would be affected by additionalstress applied Moreover the compressive strength of thebedrock was weak so the bedrock would incur large de-formations and sedimentation when under a high load

erefore the foundation of the office building was deemedto be unstable

e grouting reinforcement measure was implementedto enhance the stability of the building foundation Aftergrouting drill felling or wind inhalation did not occur andfew water leakages were found during the process of drillingthe J1 J2 and J4 boreholes According to observationsthrough the borehole TV imaging test of the J1 J3 and J4boreholes most of the cavities and fractures were filled withslurry the filling rates were greater than 85 and therebythe effect of grouting reinforcement was obvious

According to the monitoring results of the subsidenceof the office building the maximum cumulative subsidencewas 153mm and the maximum slope was 0765mmmwhich are less than the permissible values (200mm and2mmm respectively) So it indicated that the stability ofthe foundation and old gob areas was positive and thegrouting project for the large building foundation achievedsuccess

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 there are no conflicts of interestregarding the publication of this paper

Acknowledgments

anks are due to Huaibei Mining Co for providing the insitu data and project support and Dr Zhang Huaxing for histechnical guidance Support from the National Basic Re-search Program of China (973 Program 2013CB227903) and

00 60 120 180 240 300 360 420 480

Time (days)540 600 660 720 780 840 900 960

4

8

12

Subs

iden

ce (m

m)

16

Stage 1 Stage 2 Stage 3 Stage 4

W1 pointW4 pointW6 point

E1 pointE4 pointE6 point

E8 pointE9 pointE11 point

W8 pointW9 pointW11 point

Figure 12 Subsidence values of the monitoring points

Figure 13 Photograph of the office building

10 Advances in Civil Engineering

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

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an average thickness of 70m e burial depth of thebedrock was from 70 to 110m and the lithology from thebedrock surface to the roof of the No 5 coal seam wasweathered mudstone siltstone sandstone mudstonemagmatic rock and mudstone e bedrock was dividedinto three sections

e upper section was between 70 and 85m in depthHere the rock mass was more complete fractures were lessdeveloped and the lithology was mainly weathered mud-stone and siltstone But the coring rate was low so completecores could not be obtained except from the K4 boreholeAccording to the core samples taken from the K4 borehole atdepths of between 793 and 883m (Figure 3) the mudstone(circled in red) was much broken

e middle section was located at a depth of 85 to 97mHere fractures and caves were more developed the rock masswas incomplete and broken and the lithology was mainlysandstone and magmatic rocks but the coring rate was lowAccording to the core samples from the K4 borehole ata depth of 883 to 937m (Figure 4) the sandstone broke intoblocks

e bottom section was between 97 and 110m in depthHere the rockmass was fragmented a variety of rockmasseshad accumulated the lithology was mixed more cavitieswere present and drill felling or wind inhalation occurrede bottom section was unable to obtain a relatively com-plete rock core and thus it was deduced that it was a cavedzone or uncompact roadway

According to rock mechanics test results of the rocksamples (Table 1 where Rc is the uniaxial compressivestrength and Rt is the uniaxial tensile strength) thecompressive strength of the mudstone and sandstone wasless than 20MPa indicating that the compressive capacityof the bedrock was weak Moreover the mudstone wassoftened and muddied quickly when touched by water

us the bedrock would incur large deformations andsedimentation when under a high load given by thebuilding

222 Borehole TV Imaging Test A borehole TV imaging testwas used to image the entire hole wall by observing theexploration boreholes and some of the observed results arerecorded in Table 2 It can be seen that the fractures haddeveloped rock was broken from 83 to 94m in depth androck had collapsed from 94 to 102m Parts of images of theK6 borehole are shown in Figure 5 and it can be seen thatvertical fractures developed from 891 to 911m and rockcollapsed from 986m when close to the gob erefore the

From 793m to 883m

Figure 3 Characteristics of the borehole core in the upper section

From 883m to 937m

Figure 4 Characteristics of the borehole core in themiddle section

Table 1 Test results of the mechanical properties of the rocksamples

Rock samples Rc (MPa) Rt (MPa)K4 mudstone 1 249 mdashK4 sandstone 1 1913 mdash

K6 mudstone

1 065 (drying) mdash2 110 (drying) mdash3 049 (drying) mdash

Average value 075 mdashK7 mudstone 1 1926 048

K7 igneous

1 4693 mdash2 5418 mdash3 3309 mdash

Average value 4443 mdash

574 gob

572 gob

576 gob 577 gob

575 gob

573 gob571 gob

K1

K3 K6

K7K2

K5

K4

1080

1160

1240

1320

Exploratory boreholeGobs boundary

Transient electromagnetic line

Construction site boundaryOffice building boundary

Figure 2 Location of office building construction site and oldgobs

Advances in Civil Engineering 3

residual rock cavities and fractures were still present in theold gob areas and there was a high possibility for the brokenbedrock to lose their stability when under the large loadgiven by the office building

223 Height Observation of Caved and Fracture Zonese caved and fracture zones were unstable areas above theold gob areas and the range of these areas can be calculatedby observing the leakage of flushing fluid through drillingFlushing fluid was continuously poured into the borehole asthe amount of leakage increased in the cavities and fracturesthe location where the leakage increased significantly wasmarked as the top of the fracture zone and the locationwhere the flushing fluid leaked overall or drill felling fre-quently occurred was marked as the top of the caved zoneAccording to the observations of the exploration boreholesand data (Table 3) taking the maximum value the heights ofthe caved zone (Hk for short) and fracture zone (Hli forshort) were 214 and 64m respectively

23 Transient Electromagnetic Geophysical Exploration

231 Exploration Arrangement Transient ElectromagneticGeophysical Exploration (GDP-32II) was used to detect thestratigraphic conditions below the construction site Foursurvey lines were projected along the north-south directionand the 1080 1160 1240 and 1320 numbered lines were inturn projected from west to east with an adjacent spacing of80m and an adjacent measuring point spacing of 15m elocations of the survey lines are shown in Figure 2

232 Exploration Results A profile map of the apparentresistivity contours of the survey lines is shown in Figure 6

Table 2 Observation results of exploration borehole based on the TV imaging test

Borehole no Observation results using the borehole TV imaging testK1 Fractures developed at 780m depth rock collapsed from 923 to 973mK2 Fractures developed from 88 to 97m rock collapsed from 97 to 99mK3 Fractures developed rock broke from 902 to 982m and collapsed from 982 to 1022mK5 Fractures developed rock broke from 838 to 936m and collapsed from 936 to 96mK6 Fractures developed rock broke from 891 to 986m and collapsed from 986 to 1045mK7 Rock seriously broke the hole wall collapsed at 102m depth

Depth(m) N

891

896

901 911 991

906 986

901 981

E S W N N E S W N N E S W N

Figure 5 Parts of observed images of the K6 borehole

Table 3 Observation results of the Hk and Hli of the boreholes

Borehole no K1 K2 K3 K4 K5 K6 K7Hk (m) 50 30 40 64 34 36 44Hli (m) 210 135 160 214 122 116 138

4 Advances in Civil Engineering

According to the analysis in areas where the vertical depth isless than 80m the apparent resistivity value was between100 and 450Ωmiddotm and the areas were considered to bea relatively high resistance zone and speculated to be madeup of a quaternary loose layer However these areaswere transverse in scale from 100 to 260m (in Figures 6(a)and 6(b)) or 100 to 390m (in Figures 6(c) and 6(d)) and ata vertical depth of 80 to 110m the apparent resistivity valuewas between 20 and 80Ωmiddotm and the area was thereforeconsidered a relatively low resistance zone Given that therewere more residual cavities and fractures in the caved orfracture zone the sandstone water may be connected andhydrops may have formed in the gob thus causing lowresistance erefore the relatively low resistance zone wasspeculated to be a caved or fracture zone Based on theexploration results the scope of the caved and fracturezones was large and the apparent resistivity was low whichindicates that the bedrock was broken and that fractureshad developed above the old gobs hindering the stability ofthe gobs

24 Stability Evaluation of the Building FoundationDisturbance caused by the additional stress (caused bya building) on the unstable bedrock in old gob areas is one ofthe important reasons for damage to a foundation Assumethat the surface of the building foundation is a regularrectangle and the origin of the coordinate system is themidpoint of the top surface of the foundation According tothe superposition principle and integral method the addi-tional stresses (σaz for short) of the midpoint at differentdepths (z) under a uniform load are calculated using thefollowing equation [21]

⎧⎨

⎩σaz 4p

2π1113890arctg

m

n1 + n2 + m2

radic +mn

1 + n2 + m2

radic

middot1

n2 + m2 +1

1 + n21113874 11138751113891 4Ksp m l

b n

z

b

⎫⎬

⎭

(1)

where l is one-half of the long side of the rectangle b is one-half of the short side p is the vertical load and Ks is theadditional stress coefficient taken from the appendix k of thecode

Also the regarded depth is where the additional stress is10 of the gravity stress (σz for short) of the soil or rockunder the foundation as the depth affected by the load givenby the building (hz for short which the top is the ground)e office building has a twin tower structure where eachsingle building is 854m long (so l equals 427m) and 386mwide (so b equals 193m) In addition the building is 10min depth (below the ground) erefore the depth of thefoundation surface is 10m (thus hz equals z plus 10) etotal load of all 19 floors is 675 kPa the Quaternary strata are70m thick with the average bulk density of 20 kNm3 andthe average bulk density of the bedrock is 25 kNm3 So thevalue of σz can be calculated using Formula (2) and thecalculated results of σaz σz and hz are shown in Table 4

σz

20 kNm3( 1113857 times z when zle 60m

20 kNm3( 1113857 times 60

+25 kNm3( 1113857 times(zminus 60) when zgt 60m

⎧⎪⎪⎪⎨

⎪⎪⎪⎩

(2)

According to the observed and calculated results inTables 3 and 4 the height of the fracture zone (Hli) was214m and the depth affected by the load (hz) was 82meshallowest depth of the No 5 coal seam (Hs for short) was96m which was less than the sum of 214m and 82m Asshown in Figure 7 the areas affected by the load overlappedwith the fracture zone us the additional stress caused bythe office building would influence the stability of thefracture zone and might cause a large uneven settlement anddeformation of the foundation

3 Grouting Reinforcement

Owing to the instability of the building foundation therewas an extremely high risk to construct the office buildingdirectly above the old gob areas and thus the groutingreinforcement measures were needed e grouting re-inforcement of the old gob areas can effectively fill thecavities and fractures in the caved and fracture zones withthe grouting slurry by cementing the cavities or fractureswith the surrounding rock into a whole thereby improvingthe carrying capacity and stability of the coal and rock andreducing the deformation of the gob areas and the buildingfoundation In this way the safety and stability of thebuildings above the old gob areas was ensured

e scope of the grouting area delimited by the ver-tical section method [22] was larger than the building(Figure 8(a)) e movement angle of the Quaternary strata(φ) and the strike movement angle of the bedrock (δ) wereselected according to the previous statistics data and thegrouting scope along the strike was shown in the I-I strikeprofile (Figure 8(b)) e same method was adoptedalong the dip which was not shown here Eighteen groutingboreholes (borehole Z1 through Z18) were designed(Figure 8(a)) and three grouting boreholes (borehole Z3Z6 and Z7) made use of the previous exploration boreholes(boreholes K3 K6 and K7)

e cavities fractures and separation of the bedrock inthe caved and fracture zones were the main grouting areasaccording to the observed results of the exploration bore-holes and the minimum burial depth of the top of thefracture zone was 76mMoreover the floor failure caused bymining was considered and thus the range of the groutingsegment was designed to be from the 75m under the groundsurface to 3m below the floor of the No 5 coal seam emaximum grouting pressure was set to 15MPa and theinterval of the two adjacent grouting boreholes was between30 and 50m Slag cement and fly ash were used as the mainsolid grouting materials the mass ratio of cement to fly ashwas designed to be between 1 4 and 1 9 and the water-solidratio of the grouting slurry was 08 1 or 06 1 Groutingbegan on January 14 2011 and ended on March 27 2011including drilling of the 18 grouting boreholes About

Advances in Civil Engineering 5

48624 tons of cement and 266027 tons of fly ash wereconsumed Detailed information regarding the groutingtime grouting amount and reason for stopping the groutingof 11 boreholes are provided in Table 5 It can be seen that allthe grouting amounts of boreholes Z3 Z4 Z7 Z14 and Z17were more than 2000 tons and the grouting time was longerthan two weeks Moreover the location of those boreholes

was close to the coal pillars or roadways indicating that thescope of the uncompacted areas and the slurry-filling areasbelow were great Emission of slurry on the ground occurredat seven boreholes and the field inspection indicated that theuncompacted areas in the old gob areas had been filled withthe slurry effectively

4 Results and Discussion

41 Detection and Analysis of the Grouting Effect

411 Drilling of Detection Boreholes Four detection bore-holes (marked J1 through J4 shown in Figure 8(a)) wereconstructed after grouting Compared with the surroundingexploration boreholes (K3 K6 and K7 boreholes) during theprocess of drilling no drill felling or wind inhalation oc-curred and the J1 and J4 boreholes no longer incurreda water leakage (Table 6) It can be concluded that thegrouting had a favorable effect on the fracture filling

412 Borehole TV Imaging Test A borehole TV imaging testwas used to image the full borehole wall to observe thefractures in the bedrock of four detection boreholes Becausethe rock had joints and fractures the surface filled withslurry was smoother than the surface of the rock In additionthe color of the slurry was grayish white and the rock waslight grayish black but the colors of the unfilled fracturesand cavities were black According to the identification andprocessing of the images the results of filling rates of de-tection boreholes were greater than 85 And TV images ofthe J1 borehole are shown in Figure 9 the areas filled in withslurry were circled with the green lines and the unfilled areas

100 120 140 160 180 200 220 240 260 280 300 320

100 120 140 160 180 200 220 240 260 280 300 320

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash2020

015

010

0

30100

100

250

60405080150 350200

400450

40

200250

250

200

150

100

506080

300

8030 40 6050

20

(a)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

150 200

250

300

450250200

300350

400

40 80 6050

100 150

40

10080

60

5040

(b)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

5040

3025

020

0

30405060

1001508060 50

250200 400350

300 250

20015010080605040

40

(c)

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

10

60 2030 40 4040

200

350300250200150100806050

50

400 450

203040

40

350300

250200150100806050

250

5080(d)

Figure 6 Profile map of apparent resistivity contours of Transient Electromagnetic Geophysical Exploration (a) 1080 survey line (b) 1160survey line (c) 1240 survey line (d) 1320 survey line

Table 4 Depth affected by the load

z(m) n

p

(kPa) Ksσaz

(kPa)σz

(kPa)10 σz(kPa)

hz(m)

0 0 675 025 675 0 0 1025 130 675 0176 4509 500 50 3550 259 675 0092 2484 1000 100 6070 363 675 0058 1566 1425 1425 8072 373 675 0054 1458 1500 150 82

No 5 coal seam

Ground

Building

Areas affectedby the load(σaz gt 01σz)

Foundation surface

Additional stress(σaz = 01σz)

Hli = 214m

h z=

82m

Old gob areas

Hs=

96m

Figure 7 Relationship between the areas affected by the load andthe fractured zone

6 Advances in Civil Engineering

were circled with the red lines It can be seen that most of thecavities and fractures were filled with slurry and the closer tothe gobs the better of the grouting effect Comparing theafter grouting images results with the before grouting imagesresults (Table 2 and Figure 5) it was believed that themechanical properties of rock mass were strengthened andthe grouting project was successful

413 Water Injection Test Water injection tests were alsoconducted on a water column in the detection boreholesand the permeable rates of boreholes J1 J2 and J4 were0072 0992 and 0378 Lu respectively e permeable rateswere less than 1 Lu so the type was micropermeable andthus the cavities and rock fractures were filled in with the

slurry effectively after groutinge flushing fluid showed noor slow loss during drilling and thus the hydraulic link ofthe surrounding bedrock was poor In addition the bedrockwas able to maintain a certain water level when the waterlevel around it changed thereby avoiding the influence ofwater on the mudstone layer

42 Analysis of Other Factors to the Stability of the Foundation

421 Quaternary Sand Aquifer Observation from the ex-ploration boreholes in the old gob areas indicated that thecurrent groundwater level in the construction site was below100m No hydraulic connection existed between the Qua-ternary aquifer and the gobs and the change of the water

Table 5 Parameters of grouting boreholes

Drillingno

Grouting time Groutingamount Reason for

stopping groutingStarting Ending Cement

(t)Fly

ash (t)

Z3 Jan 14 Jan 29 6074 26352 Emitting of slurryat ground

Z6 Jan 14 Jan 15 340 1757 Emitting of slurryat ground

Z7 Jan 15 Feb 20 10685 42163 Emitting of slurryat ground

Z5 Jan 18 Jan 26 3854 18739 Emitting of slurryat ground

Z14 Feb 6 Feb 21 4998 25181 Reachinggrouting pressure

Z12 Feb 18 Feb 19 192 878 Emitting of slurryat ground

Z17 Feb 21 Mar27 8296 38544 Emitting of slurry

at ground

Z13 Feb 27 Mar 8 1390 7788 Reachinggrouting pressure

Z16 Mar 8 Mar27 1906 11110 mdash

Z4 Mar 10 Mar27 3963 25824 Emitting of slurry

at ground

Z8 Mar 22 Mar27 1055 9792 mdash

Table 6 Characteristics of the boreholes before and after grouting

Time Borehole Leakage observation Drillfelling

Windinhalation

Beforegrouting

K3995m to end all lostleakage more than

15m3hNo Yes

K61015m to end all lostleakage more than

15m3hNo Yes

K7899m to end all lostleakage more than

15m3hYes Yes

Aftergrouting

J1 No leaking No No

J2 899m to end a little lostleakage only 054m3h No No

J4 No leaking No No

A BMI N I

574 gob

572 gob

576 gob

Z15

Z16

Z17

Z1Z2

Z3(K3)

Z4Z5

Z6 (K6)

Z7(K7)

Z8

Z9Z10

Z11

Z12

Z13Z14

J4(Z18)

J1J2

J3

Detecting borehole

Office building boundaryGrouting range boundary Strike profile line

Grouting borehole

(a)

Q

φ

δ δ

φ

Building

Old gob areas

A BM N

Scope of the grouting treatment

hh j

I-I profile

(b)

Figure 8 (a) Grouting scope design and grouting boreholes ar-rangement (b) grouting scope of the I-I profile φ movement angleof Quaternary strata δ strike movement angle of bedrock QQuaternary strata h thickness of Quaternary strata hj thickness ofbedrock

Advances in Civil Engineering 7

level in the Quaternary sand aquifer was small ereforethe settlement of the soil layer caused by aquifer consoli-dation was small and the influence of the aquifer on thefoundation settlement was small

422 Pile Foundation Considering the heavy load given bythe building reinforcement measure of constructing pilefoundation was taken in addition to grouting reinforcemente depth of the pile foundation was 50m and the pilefoundation had good stability and large bearing capacitywhich reduced the settlement caused by compression of theQuaternary sand and soil layere strength of the backfilledrock mass and the backfilling material in the gob areasendured the additional load given by the pile foundation sothe stability of the gob areas was achieved

423 Residual Deformation of the Office BuildingFoundation Combined with the grouting effect the geo-logical conditions the building load and past experiencesan integral probability method [22] was used to calculate theresidual deformation and subsidence of the surface aftergrouting and the relevant parameters are shown in Table 7e contour line of the residual surface subsidence and theslope in the area where the office building was located areshown in Figure 10 Results showed that the maximumsurface subsidence value was 58mm and the maximumslope was 042mmm both of which are less than thepermissible subsoil deformation of a high-rise building (thepermissible subsidence was 200mm and the permissible

slope was 2mmm as taken from [21]) us constructionof the office building was made feasible

Owing to the detection and analysis of the groutingeffect the cavities and fractures of the bedrock were betterfilled and the force of the rock was changed from two-dimensional to three-dimensional which enhanced theoverall strength of the rock mass Meanwhile the stability ofthe foundation was effectively enhanced by constructing pilefoundation Since the residual deformation and subsidenceof the office building after grouting met the design re-quirements it became feasible to construct the officebuilding above the old gob areas

43 Monitoring Subsidence of the Office Building To acquirethe deformation of the office building timely during con-struction the subsidence of the building was monitored byan electronic level e actual boundary location of the officebuilding is shown in Figure 11 and twenty-two monitoringpoints were set in the buildingrsquos walls e monitoring pointnumbers are shown in Figure 11

Depth(m) N

947 973 998

1003978952

957 983 1008

E S W N N E S W N N E S W N

Figure 9 Images of the J1 detection borehole

Table 7 Parameters of surface movement after grouting

Calculated parameters Construction siteSubsidence factor 0025Main effecting angle tangent 16Displacement factor 030Mining affects the propagation angle 85Inflection point offset 0

8 Advances in Civil Engineering

e monitoring period of 930 days (from October 262012 to May 13 2015) was divided into four stages duringwhich 18 times of monitoring were conducted In stage 1(from day 0 to day 60) the building was constructed from 7floors to 17 floors so the load given by the office buildingincreased faster in this stage In stage 2 (from day 60 to day360) the building was capped and the walls were completede load increase in this stage was limited and some of themonitoring points were damaged by the construction Instage 3 (from day 360 to day 720) the whole building wascompleted and the indoor and outdoor renovation wascarried out In stage 4 (from day 720 to day 930) the buildingwas ready for use erefore the load in stage 3 and 4 wasalmost unchanged and stable

Because some of the monitoring points were damagedparts of the monitoring data were missing erefore twelvepoints (W1 W4 W6 W8 W9 W11 E1 E4 E6 E8 E9 andE11 points) were selected because their data were morecomplete and their locations were closer to the junction andmiddle of the boundary and the cumulative subsidence datawere recorded (Figure 12)

From Figure 12 it was found that all the subsidencevalues of the monitoring points increased rapidly in stage 1which might be caused by the increase of the load and therapid compression settlement of the stratum In this stagethe maximum subsidence value of point W9 was 85mmwith a sinking speed of 0142mmday e maximum slopeof points W1 and W2 was 0492mmm In stage 2 thesubsidence values changed irregularly and the subsidencevalues of some monitoring points were even negative in-dicating that the altitude of these monitoring points wereenhanced As all the monitoring points were set in the wallsthis phenomenon might be resulted from the artificialdisturbance to these monitoring points during the con-struction process of the building walls In stages 3 and 4 thesubsidence values were continuously increased but thespeeds were slowed down obviously indicating the slowcompression settlement of the strata under the stable load Inthese two stages the maximum subsidence and sinkingspeed values from point E6 were about 5mm and0009mmday respectively Comparing stage 1 with stages 3and 4 it can be seen that the subsidence values increased

rapidly with increasing load However with the increase ofthe subsidence accumulation and the slowdown of theapplied load the speed of the foundation subsidencedropped Combining Figure 11 with Figure 12 it can beseen that the subsidence values of those points located closeto the center of the old gob areas (eg points E4 and E6)were more than the points near the pillars (eg points W1and E1) In this way uneven settlement was generated andthe maximum difference of the value from points W1 andW4 was 104mm In the whole subsidence period therewas still residual subsidence because of the unfilled frac-tures in the strata Among the 22 monitoring points themaximum cumulative subsidence value was 153mm frompoint E4 and the maximum slope was 0765mmm frompoints W1 and W2 However compared with the per-missible subsoil subsidence (200mm) and permissiblesubsoil slope (2mmm) the maximum subsidence andslope were far less than the permissible values e officebuilding was built successfully after grouting (a photographof building is shown in Figure 13) cracking or otherdamages during construction did not occur us thestability of the foundation was enhanced greatly by the

4543

4147

4951

5355

57

5553

51

5759

Office building

(a)

05

03

010

3

01

01

Office building

(b)

Figure 10 Map of residual surface subsidence and slope contours in the area where the office building was located (a) map of residualsurface subsidence contours unit as mm (b) map of residual slope contours unit as mmm

W6W7 W8 E8 E7

E6

E5

E4

E1E2E13

E11E10

E9W9

W10

W11

W1W2W3

W4

W5

574 gob

572 gob

576 gob

Monitoring points

Figure 11 Location of the building and the monitoring points

Advances in Civil Engineering 9

grouting reinforcement which proved that the groutingreinforcement of the office building can be adopted forother large buildings constructed over old gob areas

5 Conclusions

According to the observed results from borehole explorationand the TV imaging test all 7 exploration boreholes incurredwind inhalation or drill felling e bedrock chosen for thebuilding construction had been broken and serious frac-tures had developed above the old gob areas us thestability of the gob areas was poor

e depth affected by the load (caused by the officebuilding) was 85m and the largest height of the fracturezone induced by mining was 214m And the shallowestburial depth of the No 5 coal seam was 96m and thereforethe fracture zone overlapped with the areas affected by theload of which the stability would be affected by additionalstress applied Moreover the compressive strength of thebedrock was weak so the bedrock would incur large de-formations and sedimentation when under a high load

erefore the foundation of the office building was deemedto be unstable

e grouting reinforcement measure was implementedto enhance the stability of the building foundation Aftergrouting drill felling or wind inhalation did not occur andfew water leakages were found during the process of drillingthe J1 J2 and J4 boreholes According to observationsthrough the borehole TV imaging test of the J1 J3 and J4boreholes most of the cavities and fractures were filled withslurry the filling rates were greater than 85 and therebythe effect of grouting reinforcement was obvious

According to the monitoring results of the subsidenceof the office building the maximum cumulative subsidencewas 153mm and the maximum slope was 0765mmmwhich are less than the permissible values (200mm and2mmm respectively) So it indicated that the stability ofthe foundation and old gob areas was positive and thegrouting project for the large building foundation achievedsuccess

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 there are no conflicts of interestregarding the publication of this paper

Acknowledgments

anks are due to Huaibei Mining Co for providing the insitu data and project support and Dr Zhang Huaxing for histechnical guidance Support from the National Basic Re-search Program of China (973 Program 2013CB227903) and

00 60 120 180 240 300 360 420 480

Time (days)540 600 660 720 780 840 900 960

4

8

12

Subs

iden

ce (m

m)

16

Stage 1 Stage 2 Stage 3 Stage 4

W1 pointW4 pointW6 point

E1 pointE4 pointE6 point

E8 pointE9 pointE11 point

W8 pointW9 pointW11 point

Figure 12 Subsidence values of the monitoring points

Figure 13 Photograph of the office building

10 Advances in Civil Engineering

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

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residual rock cavities and fractures were still present in theold gob areas and there was a high possibility for the brokenbedrock to lose their stability when under the large loadgiven by the office building

223 Height Observation of Caved and Fracture Zonese caved and fracture zones were unstable areas above theold gob areas and the range of these areas can be calculatedby observing the leakage of flushing fluid through drillingFlushing fluid was continuously poured into the borehole asthe amount of leakage increased in the cavities and fracturesthe location where the leakage increased significantly wasmarked as the top of the fracture zone and the locationwhere the flushing fluid leaked overall or drill felling fre-quently occurred was marked as the top of the caved zoneAccording to the observations of the exploration boreholesand data (Table 3) taking the maximum value the heights ofthe caved zone (Hk for short) and fracture zone (Hli forshort) were 214 and 64m respectively

23 Transient Electromagnetic Geophysical Exploration

231 Exploration Arrangement Transient ElectromagneticGeophysical Exploration (GDP-32II) was used to detect thestratigraphic conditions below the construction site Foursurvey lines were projected along the north-south directionand the 1080 1160 1240 and 1320 numbered lines were inturn projected from west to east with an adjacent spacing of80m and an adjacent measuring point spacing of 15m elocations of the survey lines are shown in Figure 2

232 Exploration Results A profile map of the apparentresistivity contours of the survey lines is shown in Figure 6

Table 2 Observation results of exploration borehole based on the TV imaging test

Borehole no Observation results using the borehole TV imaging testK1 Fractures developed at 780m depth rock collapsed from 923 to 973mK2 Fractures developed from 88 to 97m rock collapsed from 97 to 99mK3 Fractures developed rock broke from 902 to 982m and collapsed from 982 to 1022mK5 Fractures developed rock broke from 838 to 936m and collapsed from 936 to 96mK6 Fractures developed rock broke from 891 to 986m and collapsed from 986 to 1045mK7 Rock seriously broke the hole wall collapsed at 102m depth

Depth(m) N

891

896

901 911 991

906 986

901 981

E S W N N E S W N N E S W N

Figure 5 Parts of observed images of the K6 borehole

Table 3 Observation results of the Hk and Hli of the boreholes

Borehole no K1 K2 K3 K4 K5 K6 K7Hk (m) 50 30 40 64 34 36 44Hli (m) 210 135 160 214 122 116 138

4 Advances in Civil Engineering

According to the analysis in areas where the vertical depth isless than 80m the apparent resistivity value was between100 and 450Ωmiddotm and the areas were considered to bea relatively high resistance zone and speculated to be madeup of a quaternary loose layer However these areaswere transverse in scale from 100 to 260m (in Figures 6(a)and 6(b)) or 100 to 390m (in Figures 6(c) and 6(d)) and ata vertical depth of 80 to 110m the apparent resistivity valuewas between 20 and 80Ωmiddotm and the area was thereforeconsidered a relatively low resistance zone Given that therewere more residual cavities and fractures in the caved orfracture zone the sandstone water may be connected andhydrops may have formed in the gob thus causing lowresistance erefore the relatively low resistance zone wasspeculated to be a caved or fracture zone Based on theexploration results the scope of the caved and fracturezones was large and the apparent resistivity was low whichindicates that the bedrock was broken and that fractureshad developed above the old gobs hindering the stability ofthe gobs

24 Stability Evaluation of the Building FoundationDisturbance caused by the additional stress (caused bya building) on the unstable bedrock in old gob areas is one ofthe important reasons for damage to a foundation Assumethat the surface of the building foundation is a regularrectangle and the origin of the coordinate system is themidpoint of the top surface of the foundation According tothe superposition principle and integral method the addi-tional stresses (σaz for short) of the midpoint at differentdepths (z) under a uniform load are calculated using thefollowing equation [21]

⎧⎨

⎩σaz 4p

2π1113890arctg

m

n1 + n2 + m2

radic +mn

1 + n2 + m2

radic

middot1

n2 + m2 +1

1 + n21113874 11138751113891 4Ksp m l

b n

z

b

⎫⎬

⎭

(1)

where l is one-half of the long side of the rectangle b is one-half of the short side p is the vertical load and Ks is theadditional stress coefficient taken from the appendix k of thecode

Also the regarded depth is where the additional stress is10 of the gravity stress (σz for short) of the soil or rockunder the foundation as the depth affected by the load givenby the building (hz for short which the top is the ground)e office building has a twin tower structure where eachsingle building is 854m long (so l equals 427m) and 386mwide (so b equals 193m) In addition the building is 10min depth (below the ground) erefore the depth of thefoundation surface is 10m (thus hz equals z plus 10) etotal load of all 19 floors is 675 kPa the Quaternary strata are70m thick with the average bulk density of 20 kNm3 andthe average bulk density of the bedrock is 25 kNm3 So thevalue of σz can be calculated using Formula (2) and thecalculated results of σaz σz and hz are shown in Table 4

σz

20 kNm3( 1113857 times z when zle 60m

20 kNm3( 1113857 times 60

+25 kNm3( 1113857 times(zminus 60) when zgt 60m

⎧⎪⎪⎪⎨

⎪⎪⎪⎩

(2)

According to the observed and calculated results inTables 3 and 4 the height of the fracture zone (Hli) was214m and the depth affected by the load (hz) was 82meshallowest depth of the No 5 coal seam (Hs for short) was96m which was less than the sum of 214m and 82m Asshown in Figure 7 the areas affected by the load overlappedwith the fracture zone us the additional stress caused bythe office building would influence the stability of thefracture zone and might cause a large uneven settlement anddeformation of the foundation

3 Grouting Reinforcement

Owing to the instability of the building foundation therewas an extremely high risk to construct the office buildingdirectly above the old gob areas and thus the groutingreinforcement measures were needed e grouting re-inforcement of the old gob areas can effectively fill thecavities and fractures in the caved and fracture zones withthe grouting slurry by cementing the cavities or fractureswith the surrounding rock into a whole thereby improvingthe carrying capacity and stability of the coal and rock andreducing the deformation of the gob areas and the buildingfoundation In this way the safety and stability of thebuildings above the old gob areas was ensured

e scope of the grouting area delimited by the ver-tical section method [22] was larger than the building(Figure 8(a)) e movement angle of the Quaternary strata(φ) and the strike movement angle of the bedrock (δ) wereselected according to the previous statistics data and thegrouting scope along the strike was shown in the I-I strikeprofile (Figure 8(b)) e same method was adoptedalong the dip which was not shown here Eighteen groutingboreholes (borehole Z1 through Z18) were designed(Figure 8(a)) and three grouting boreholes (borehole Z3Z6 and Z7) made use of the previous exploration boreholes(boreholes K3 K6 and K7)

e cavities fractures and separation of the bedrock inthe caved and fracture zones were the main grouting areasaccording to the observed results of the exploration bore-holes and the minimum burial depth of the top of thefracture zone was 76mMoreover the floor failure caused bymining was considered and thus the range of the groutingsegment was designed to be from the 75m under the groundsurface to 3m below the floor of the No 5 coal seam emaximum grouting pressure was set to 15MPa and theinterval of the two adjacent grouting boreholes was between30 and 50m Slag cement and fly ash were used as the mainsolid grouting materials the mass ratio of cement to fly ashwas designed to be between 1 4 and 1 9 and the water-solidratio of the grouting slurry was 08 1 or 06 1 Groutingbegan on January 14 2011 and ended on March 27 2011including drilling of the 18 grouting boreholes About

Advances in Civil Engineering 5

48624 tons of cement and 266027 tons of fly ash wereconsumed Detailed information regarding the groutingtime grouting amount and reason for stopping the groutingof 11 boreholes are provided in Table 5 It can be seen that allthe grouting amounts of boreholes Z3 Z4 Z7 Z14 and Z17were more than 2000 tons and the grouting time was longerthan two weeks Moreover the location of those boreholes

was close to the coal pillars or roadways indicating that thescope of the uncompacted areas and the slurry-filling areasbelow were great Emission of slurry on the ground occurredat seven boreholes and the field inspection indicated that theuncompacted areas in the old gob areas had been filled withthe slurry effectively

4 Results and Discussion

41 Detection and Analysis of the Grouting Effect

411 Drilling of Detection Boreholes Four detection bore-holes (marked J1 through J4 shown in Figure 8(a)) wereconstructed after grouting Compared with the surroundingexploration boreholes (K3 K6 and K7 boreholes) during theprocess of drilling no drill felling or wind inhalation oc-curred and the J1 and J4 boreholes no longer incurreda water leakage (Table 6) It can be concluded that thegrouting had a favorable effect on the fracture filling

412 Borehole TV Imaging Test A borehole TV imaging testwas used to image the full borehole wall to observe thefractures in the bedrock of four detection boreholes Becausethe rock had joints and fractures the surface filled withslurry was smoother than the surface of the rock In additionthe color of the slurry was grayish white and the rock waslight grayish black but the colors of the unfilled fracturesand cavities were black According to the identification andprocessing of the images the results of filling rates of de-tection boreholes were greater than 85 And TV images ofthe J1 borehole are shown in Figure 9 the areas filled in withslurry were circled with the green lines and the unfilled areas

100 120 140 160 180 200 220 240 260 280 300 320

100 120 140 160 180 200 220 240 260 280 300 320

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash2020

015

010

0

30100

100

250

60405080150 350200

400450

40

200250

250

200

150

100

506080

300

8030 40 6050

20

(a)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

150 200

250

300

450250200

300350

400

40 80 6050

100 150

40

10080

60

5040

(b)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

5040

3025

020

0

30405060

1001508060 50

250200 400350

300 250

20015010080605040

40

(c)

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

10

60 2030 40 4040

200

350300250200150100806050

50

400 450

203040

40

350300

250200150100806050

250

5080(d)

Figure 6 Profile map of apparent resistivity contours of Transient Electromagnetic Geophysical Exploration (a) 1080 survey line (b) 1160survey line (c) 1240 survey line (d) 1320 survey line

Table 4 Depth affected by the load

z(m) n

p

(kPa) Ksσaz

(kPa)σz

(kPa)10 σz(kPa)

hz(m)

0 0 675 025 675 0 0 1025 130 675 0176 4509 500 50 3550 259 675 0092 2484 1000 100 6070 363 675 0058 1566 1425 1425 8072 373 675 0054 1458 1500 150 82

No 5 coal seam

Ground

Building

Areas affectedby the load(σaz gt 01σz)

Foundation surface

Additional stress(σaz = 01σz)

Hli = 214m

h z=

82m

Old gob areas

Hs=

96m

Figure 7 Relationship between the areas affected by the load andthe fractured zone

6 Advances in Civil Engineering

were circled with the red lines It can be seen that most of thecavities and fractures were filled with slurry and the closer tothe gobs the better of the grouting effect Comparing theafter grouting images results with the before grouting imagesresults (Table 2 and Figure 5) it was believed that themechanical properties of rock mass were strengthened andthe grouting project was successful

413 Water Injection Test Water injection tests were alsoconducted on a water column in the detection boreholesand the permeable rates of boreholes J1 J2 and J4 were0072 0992 and 0378 Lu respectively e permeable rateswere less than 1 Lu so the type was micropermeable andthus the cavities and rock fractures were filled in with the

slurry effectively after groutinge flushing fluid showed noor slow loss during drilling and thus the hydraulic link ofthe surrounding bedrock was poor In addition the bedrockwas able to maintain a certain water level when the waterlevel around it changed thereby avoiding the influence ofwater on the mudstone layer

42 Analysis of Other Factors to the Stability of the Foundation

421 Quaternary Sand Aquifer Observation from the ex-ploration boreholes in the old gob areas indicated that thecurrent groundwater level in the construction site was below100m No hydraulic connection existed between the Qua-ternary aquifer and the gobs and the change of the water

Table 5 Parameters of grouting boreholes

Drillingno

Grouting time Groutingamount Reason for

stopping groutingStarting Ending Cement

(t)Fly

ash (t)

Z3 Jan 14 Jan 29 6074 26352 Emitting of slurryat ground

Z6 Jan 14 Jan 15 340 1757 Emitting of slurryat ground

Z7 Jan 15 Feb 20 10685 42163 Emitting of slurryat ground

Z5 Jan 18 Jan 26 3854 18739 Emitting of slurryat ground

Z14 Feb 6 Feb 21 4998 25181 Reachinggrouting pressure

Z12 Feb 18 Feb 19 192 878 Emitting of slurryat ground

Z17 Feb 21 Mar27 8296 38544 Emitting of slurry

at ground

Z13 Feb 27 Mar 8 1390 7788 Reachinggrouting pressure

Z16 Mar 8 Mar27 1906 11110 mdash

Z4 Mar 10 Mar27 3963 25824 Emitting of slurry

at ground

Z8 Mar 22 Mar27 1055 9792 mdash

Table 6 Characteristics of the boreholes before and after grouting

Time Borehole Leakage observation Drillfelling

Windinhalation

Beforegrouting

K3995m to end all lostleakage more than

15m3hNo Yes

K61015m to end all lostleakage more than

15m3hNo Yes

K7899m to end all lostleakage more than

15m3hYes Yes

Aftergrouting

J1 No leaking No No

J2 899m to end a little lostleakage only 054m3h No No

J4 No leaking No No

A BMI N I

574 gob

572 gob

576 gob

Z15

Z16

Z17

Z1Z2

Z3(K3)

Z4Z5

Z6 (K6)

Z7(K7)

Z8

Z9Z10

Z11

Z12

Z13Z14

J4(Z18)

J1J2

J3

Detecting borehole

Office building boundaryGrouting range boundary Strike profile line

Grouting borehole

(a)

Q

φ

δ δ

φ

Building

Old gob areas

A BM N

Scope of the grouting treatment

hh j

I-I profile

(b)

Figure 8 (a) Grouting scope design and grouting boreholes ar-rangement (b) grouting scope of the I-I profile φ movement angleof Quaternary strata δ strike movement angle of bedrock QQuaternary strata h thickness of Quaternary strata hj thickness ofbedrock

Advances in Civil Engineering 7

level in the Quaternary sand aquifer was small ereforethe settlement of the soil layer caused by aquifer consoli-dation was small and the influence of the aquifer on thefoundation settlement was small

422 Pile Foundation Considering the heavy load given bythe building reinforcement measure of constructing pilefoundation was taken in addition to grouting reinforcemente depth of the pile foundation was 50m and the pilefoundation had good stability and large bearing capacitywhich reduced the settlement caused by compression of theQuaternary sand and soil layere strength of the backfilledrock mass and the backfilling material in the gob areasendured the additional load given by the pile foundation sothe stability of the gob areas was achieved

423 Residual Deformation of the Office BuildingFoundation Combined with the grouting effect the geo-logical conditions the building load and past experiencesan integral probability method [22] was used to calculate theresidual deformation and subsidence of the surface aftergrouting and the relevant parameters are shown in Table 7e contour line of the residual surface subsidence and theslope in the area where the office building was located areshown in Figure 10 Results showed that the maximumsurface subsidence value was 58mm and the maximumslope was 042mmm both of which are less than thepermissible subsoil deformation of a high-rise building (thepermissible subsidence was 200mm and the permissible

slope was 2mmm as taken from [21]) us constructionof the office building was made feasible

Owing to the detection and analysis of the groutingeffect the cavities and fractures of the bedrock were betterfilled and the force of the rock was changed from two-dimensional to three-dimensional which enhanced theoverall strength of the rock mass Meanwhile the stability ofthe foundation was effectively enhanced by constructing pilefoundation Since the residual deformation and subsidenceof the office building after grouting met the design re-quirements it became feasible to construct the officebuilding above the old gob areas

43 Monitoring Subsidence of the Office Building To acquirethe deformation of the office building timely during con-struction the subsidence of the building was monitored byan electronic level e actual boundary location of the officebuilding is shown in Figure 11 and twenty-two monitoringpoints were set in the buildingrsquos walls e monitoring pointnumbers are shown in Figure 11

Depth(m) N

947 973 998

1003978952

957 983 1008

E S W N N E S W N N E S W N

Figure 9 Images of the J1 detection borehole

Table 7 Parameters of surface movement after grouting

Calculated parameters Construction siteSubsidence factor 0025Main effecting angle tangent 16Displacement factor 030Mining affects the propagation angle 85Inflection point offset 0

8 Advances in Civil Engineering

e monitoring period of 930 days (from October 262012 to May 13 2015) was divided into four stages duringwhich 18 times of monitoring were conducted In stage 1(from day 0 to day 60) the building was constructed from 7floors to 17 floors so the load given by the office buildingincreased faster in this stage In stage 2 (from day 60 to day360) the building was capped and the walls were completede load increase in this stage was limited and some of themonitoring points were damaged by the construction Instage 3 (from day 360 to day 720) the whole building wascompleted and the indoor and outdoor renovation wascarried out In stage 4 (from day 720 to day 930) the buildingwas ready for use erefore the load in stage 3 and 4 wasalmost unchanged and stable

Because some of the monitoring points were damagedparts of the monitoring data were missing erefore twelvepoints (W1 W4 W6 W8 W9 W11 E1 E4 E6 E8 E9 andE11 points) were selected because their data were morecomplete and their locations were closer to the junction andmiddle of the boundary and the cumulative subsidence datawere recorded (Figure 12)

From Figure 12 it was found that all the subsidencevalues of the monitoring points increased rapidly in stage 1which might be caused by the increase of the load and therapid compression settlement of the stratum In this stagethe maximum subsidence value of point W9 was 85mmwith a sinking speed of 0142mmday e maximum slopeof points W1 and W2 was 0492mmm In stage 2 thesubsidence values changed irregularly and the subsidencevalues of some monitoring points were even negative in-dicating that the altitude of these monitoring points wereenhanced As all the monitoring points were set in the wallsthis phenomenon might be resulted from the artificialdisturbance to these monitoring points during the con-struction process of the building walls In stages 3 and 4 thesubsidence values were continuously increased but thespeeds were slowed down obviously indicating the slowcompression settlement of the strata under the stable load Inthese two stages the maximum subsidence and sinkingspeed values from point E6 were about 5mm and0009mmday respectively Comparing stage 1 with stages 3and 4 it can be seen that the subsidence values increased

rapidly with increasing load However with the increase ofthe subsidence accumulation and the slowdown of theapplied load the speed of the foundation subsidencedropped Combining Figure 11 with Figure 12 it can beseen that the subsidence values of those points located closeto the center of the old gob areas (eg points E4 and E6)were more than the points near the pillars (eg points W1and E1) In this way uneven settlement was generated andthe maximum difference of the value from points W1 andW4 was 104mm In the whole subsidence period therewas still residual subsidence because of the unfilled frac-tures in the strata Among the 22 monitoring points themaximum cumulative subsidence value was 153mm frompoint E4 and the maximum slope was 0765mmm frompoints W1 and W2 However compared with the per-missible subsoil subsidence (200mm) and permissiblesubsoil slope (2mmm) the maximum subsidence andslope were far less than the permissible values e officebuilding was built successfully after grouting (a photographof building is shown in Figure 13) cracking or otherdamages during construction did not occur us thestability of the foundation was enhanced greatly by the

4543

4147

4951

5355

57

5553

51

5759

Office building

(a)

05

03

010

3

01

01

Office building

(b)

Figure 10 Map of residual surface subsidence and slope contours in the area where the office building was located (a) map of residualsurface subsidence contours unit as mm (b) map of residual slope contours unit as mmm

W6W7 W8 E8 E7

E6

E5

E4

E1E2E13

E11E10

E9W9

W10

W11

W1W2W3

W4

W5

574 gob

572 gob

576 gob

Monitoring points

Figure 11 Location of the building and the monitoring points

Advances in Civil Engineering 9

grouting reinforcement which proved that the groutingreinforcement of the office building can be adopted forother large buildings constructed over old gob areas

5 Conclusions

According to the observed results from borehole explorationand the TV imaging test all 7 exploration boreholes incurredwind inhalation or drill felling e bedrock chosen for thebuilding construction had been broken and serious frac-tures had developed above the old gob areas us thestability of the gob areas was poor

e depth affected by the load (caused by the officebuilding) was 85m and the largest height of the fracturezone induced by mining was 214m And the shallowestburial depth of the No 5 coal seam was 96m and thereforethe fracture zone overlapped with the areas affected by theload of which the stability would be affected by additionalstress applied Moreover the compressive strength of thebedrock was weak so the bedrock would incur large de-formations and sedimentation when under a high load

erefore the foundation of the office building was deemedto be unstable

e grouting reinforcement measure was implementedto enhance the stability of the building foundation Aftergrouting drill felling or wind inhalation did not occur andfew water leakages were found during the process of drillingthe J1 J2 and J4 boreholes According to observationsthrough the borehole TV imaging test of the J1 J3 and J4boreholes most of the cavities and fractures were filled withslurry the filling rates were greater than 85 and therebythe effect of grouting reinforcement was obvious

According to the monitoring results of the subsidenceof the office building the maximum cumulative subsidencewas 153mm and the maximum slope was 0765mmmwhich are less than the permissible values (200mm and2mmm respectively) So it indicated that the stability ofthe foundation and old gob areas was positive and thegrouting project for the large building foundation achievedsuccess

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 there are no conflicts of interestregarding the publication of this paper

Acknowledgments

anks are due to Huaibei Mining Co for providing the insitu data and project support and Dr Zhang Huaxing for histechnical guidance Support from the National Basic Re-search Program of China (973 Program 2013CB227903) and

00 60 120 180 240 300 360 420 480

Time (days)540 600 660 720 780 840 900 960

4

8

12

Subs

iden

ce (m

m)

16

Stage 1 Stage 2 Stage 3 Stage 4

W1 pointW4 pointW6 point

E1 pointE4 pointE6 point

E8 pointE9 pointE11 point

W8 pointW9 pointW11 point

Figure 12 Subsidence values of the monitoring points

Figure 13 Photograph of the office building

10 Advances in Civil Engineering

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

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According to the analysis in areas where the vertical depth isless than 80m the apparent resistivity value was between100 and 450Ωmiddotm and the areas were considered to bea relatively high resistance zone and speculated to be madeup of a quaternary loose layer However these areaswere transverse in scale from 100 to 260m (in Figures 6(a)and 6(b)) or 100 to 390m (in Figures 6(c) and 6(d)) and ata vertical depth of 80 to 110m the apparent resistivity valuewas between 20 and 80Ωmiddotm and the area was thereforeconsidered a relatively low resistance zone Given that therewere more residual cavities and fractures in the caved orfracture zone the sandstone water may be connected andhydrops may have formed in the gob thus causing lowresistance erefore the relatively low resistance zone wasspeculated to be a caved or fracture zone Based on theexploration results the scope of the caved and fracturezones was large and the apparent resistivity was low whichindicates that the bedrock was broken and that fractureshad developed above the old gobs hindering the stability ofthe gobs

24 Stability Evaluation of the Building FoundationDisturbance caused by the additional stress (caused bya building) on the unstable bedrock in old gob areas is one ofthe important reasons for damage to a foundation Assumethat the surface of the building foundation is a regularrectangle and the origin of the coordinate system is themidpoint of the top surface of the foundation According tothe superposition principle and integral method the addi-tional stresses (σaz for short) of the midpoint at differentdepths (z) under a uniform load are calculated using thefollowing equation [21]

⎧⎨

⎩σaz 4p

2π1113890arctg

m

n1 + n2 + m2

radic +mn

1 + n2 + m2

radic

middot1

n2 + m2 +1

1 + n21113874 11138751113891 4Ksp m l

b n

z

b

⎫⎬

⎭

(1)

where l is one-half of the long side of the rectangle b is one-half of the short side p is the vertical load and Ks is theadditional stress coefficient taken from the appendix k of thecode

Also the regarded depth is where the additional stress is10 of the gravity stress (σz for short) of the soil or rockunder the foundation as the depth affected by the load givenby the building (hz for short which the top is the ground)e office building has a twin tower structure where eachsingle building is 854m long (so l equals 427m) and 386mwide (so b equals 193m) In addition the building is 10min depth (below the ground) erefore the depth of thefoundation surface is 10m (thus hz equals z plus 10) etotal load of all 19 floors is 675 kPa the Quaternary strata are70m thick with the average bulk density of 20 kNm3 andthe average bulk density of the bedrock is 25 kNm3 So thevalue of σz can be calculated using Formula (2) and thecalculated results of σaz σz and hz are shown in Table 4

σz

20 kNm3( 1113857 times z when zle 60m

20 kNm3( 1113857 times 60

+25 kNm3( 1113857 times(zminus 60) when zgt 60m

⎧⎪⎪⎪⎨

⎪⎪⎪⎩

(2)

According to the observed and calculated results inTables 3 and 4 the height of the fracture zone (Hli) was214m and the depth affected by the load (hz) was 82meshallowest depth of the No 5 coal seam (Hs for short) was96m which was less than the sum of 214m and 82m Asshown in Figure 7 the areas affected by the load overlappedwith the fracture zone us the additional stress caused bythe office building would influence the stability of thefracture zone and might cause a large uneven settlement anddeformation of the foundation

3 Grouting Reinforcement

Owing to the instability of the building foundation therewas an extremely high risk to construct the office buildingdirectly above the old gob areas and thus the groutingreinforcement measures were needed e grouting re-inforcement of the old gob areas can effectively fill thecavities and fractures in the caved and fracture zones withthe grouting slurry by cementing the cavities or fractureswith the surrounding rock into a whole thereby improvingthe carrying capacity and stability of the coal and rock andreducing the deformation of the gob areas and the buildingfoundation In this way the safety and stability of thebuildings above the old gob areas was ensured

e scope of the grouting area delimited by the ver-tical section method [22] was larger than the building(Figure 8(a)) e movement angle of the Quaternary strata(φ) and the strike movement angle of the bedrock (δ) wereselected according to the previous statistics data and thegrouting scope along the strike was shown in the I-I strikeprofile (Figure 8(b)) e same method was adoptedalong the dip which was not shown here Eighteen groutingboreholes (borehole Z1 through Z18) were designed(Figure 8(a)) and three grouting boreholes (borehole Z3Z6 and Z7) made use of the previous exploration boreholes(boreholes K3 K6 and K7)

e cavities fractures and separation of the bedrock inthe caved and fracture zones were the main grouting areasaccording to the observed results of the exploration bore-holes and the minimum burial depth of the top of thefracture zone was 76mMoreover the floor failure caused bymining was considered and thus the range of the groutingsegment was designed to be from the 75m under the groundsurface to 3m below the floor of the No 5 coal seam emaximum grouting pressure was set to 15MPa and theinterval of the two adjacent grouting boreholes was between30 and 50m Slag cement and fly ash were used as the mainsolid grouting materials the mass ratio of cement to fly ashwas designed to be between 1 4 and 1 9 and the water-solidratio of the grouting slurry was 08 1 or 06 1 Groutingbegan on January 14 2011 and ended on March 27 2011including drilling of the 18 grouting boreholes About

Advances in Civil Engineering 5

48624 tons of cement and 266027 tons of fly ash wereconsumed Detailed information regarding the groutingtime grouting amount and reason for stopping the groutingof 11 boreholes are provided in Table 5 It can be seen that allthe grouting amounts of boreholes Z3 Z4 Z7 Z14 and Z17were more than 2000 tons and the grouting time was longerthan two weeks Moreover the location of those boreholes

was close to the coal pillars or roadways indicating that thescope of the uncompacted areas and the slurry-filling areasbelow were great Emission of slurry on the ground occurredat seven boreholes and the field inspection indicated that theuncompacted areas in the old gob areas had been filled withthe slurry effectively

4 Results and Discussion

41 Detection and Analysis of the Grouting Effect

411 Drilling of Detection Boreholes Four detection bore-holes (marked J1 through J4 shown in Figure 8(a)) wereconstructed after grouting Compared with the surroundingexploration boreholes (K3 K6 and K7 boreholes) during theprocess of drilling no drill felling or wind inhalation oc-curred and the J1 and J4 boreholes no longer incurreda water leakage (Table 6) It can be concluded that thegrouting had a favorable effect on the fracture filling

412 Borehole TV Imaging Test A borehole TV imaging testwas used to image the full borehole wall to observe thefractures in the bedrock of four detection boreholes Becausethe rock had joints and fractures the surface filled withslurry was smoother than the surface of the rock In additionthe color of the slurry was grayish white and the rock waslight grayish black but the colors of the unfilled fracturesand cavities were black According to the identification andprocessing of the images the results of filling rates of de-tection boreholes were greater than 85 And TV images ofthe J1 borehole are shown in Figure 9 the areas filled in withslurry were circled with the green lines and the unfilled areas

100 120 140 160 180 200 220 240 260 280 300 320

100 120 140 160 180 200 220 240 260 280 300 320

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash2020

015

010

0

30100

100

250

60405080150 350200

400450

40

200250

250

200

150

100

506080

300

8030 40 6050

20

(a)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

150 200

250

300

450250200

300350

400

40 80 6050

100 150

40

10080

60

5040

(b)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

5040

3025

020

0

30405060

1001508060 50

250200 400350

300 250

20015010080605040

40

(c)

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

10

60 2030 40 4040

200

350300250200150100806050

50

400 450

203040

40

350300

250200150100806050

250

5080(d)

Figure 6 Profile map of apparent resistivity contours of Transient Electromagnetic Geophysical Exploration (a) 1080 survey line (b) 1160survey line (c) 1240 survey line (d) 1320 survey line

Table 4 Depth affected by the load

z(m) n

p

(kPa) Ksσaz

(kPa)σz

(kPa)10 σz(kPa)

hz(m)

0 0 675 025 675 0 0 1025 130 675 0176 4509 500 50 3550 259 675 0092 2484 1000 100 6070 363 675 0058 1566 1425 1425 8072 373 675 0054 1458 1500 150 82

No 5 coal seam

Ground

Building

Areas affectedby the load(σaz gt 01σz)

Foundation surface

Additional stress(σaz = 01σz)

Hli = 214m

h z=

82m

Old gob areas

Hs=

96m

Figure 7 Relationship between the areas affected by the load andthe fractured zone

6 Advances in Civil Engineering

were circled with the red lines It can be seen that most of thecavities and fractures were filled with slurry and the closer tothe gobs the better of the grouting effect Comparing theafter grouting images results with the before grouting imagesresults (Table 2 and Figure 5) it was believed that themechanical properties of rock mass were strengthened andthe grouting project was successful

413 Water Injection Test Water injection tests were alsoconducted on a water column in the detection boreholesand the permeable rates of boreholes J1 J2 and J4 were0072 0992 and 0378 Lu respectively e permeable rateswere less than 1 Lu so the type was micropermeable andthus the cavities and rock fractures were filled in with the

slurry effectively after groutinge flushing fluid showed noor slow loss during drilling and thus the hydraulic link ofthe surrounding bedrock was poor In addition the bedrockwas able to maintain a certain water level when the waterlevel around it changed thereby avoiding the influence ofwater on the mudstone layer

42 Analysis of Other Factors to the Stability of the Foundation

421 Quaternary Sand Aquifer Observation from the ex-ploration boreholes in the old gob areas indicated that thecurrent groundwater level in the construction site was below100m No hydraulic connection existed between the Qua-ternary aquifer and the gobs and the change of the water

Table 5 Parameters of grouting boreholes

Drillingno

Grouting time Groutingamount Reason for

stopping groutingStarting Ending Cement

(t)Fly

ash (t)

Z3 Jan 14 Jan 29 6074 26352 Emitting of slurryat ground

Z6 Jan 14 Jan 15 340 1757 Emitting of slurryat ground

Z7 Jan 15 Feb 20 10685 42163 Emitting of slurryat ground

Z5 Jan 18 Jan 26 3854 18739 Emitting of slurryat ground

Z14 Feb 6 Feb 21 4998 25181 Reachinggrouting pressure

Z12 Feb 18 Feb 19 192 878 Emitting of slurryat ground

Z17 Feb 21 Mar27 8296 38544 Emitting of slurry

at ground

Z13 Feb 27 Mar 8 1390 7788 Reachinggrouting pressure

Z16 Mar 8 Mar27 1906 11110 mdash

Z4 Mar 10 Mar27 3963 25824 Emitting of slurry

at ground

Z8 Mar 22 Mar27 1055 9792 mdash

Table 6 Characteristics of the boreholes before and after grouting

Time Borehole Leakage observation Drillfelling

Windinhalation

Beforegrouting

K3995m to end all lostleakage more than

15m3hNo Yes

K61015m to end all lostleakage more than

15m3hNo Yes

K7899m to end all lostleakage more than

15m3hYes Yes

Aftergrouting

J1 No leaking No No

J2 899m to end a little lostleakage only 054m3h No No

J4 No leaking No No

A BMI N I

574 gob

572 gob

576 gob

Z15

Z16

Z17

Z1Z2

Z3(K3)

Z4Z5

Z6 (K6)

Z7(K7)

Z8

Z9Z10

Z11

Z12

Z13Z14

J4(Z18)

J1J2

J3

Detecting borehole

Office building boundaryGrouting range boundary Strike profile line

Grouting borehole

(a)

Q

φ

δ δ

φ

Building

Old gob areas

A BM N

Scope of the grouting treatment

hh j

I-I profile

(b)

Figure 8 (a) Grouting scope design and grouting boreholes ar-rangement (b) grouting scope of the I-I profile φ movement angleof Quaternary strata δ strike movement angle of bedrock QQuaternary strata h thickness of Quaternary strata hj thickness ofbedrock

Advances in Civil Engineering 7

level in the Quaternary sand aquifer was small ereforethe settlement of the soil layer caused by aquifer consoli-dation was small and the influence of the aquifer on thefoundation settlement was small

422 Pile Foundation Considering the heavy load given bythe building reinforcement measure of constructing pilefoundation was taken in addition to grouting reinforcemente depth of the pile foundation was 50m and the pilefoundation had good stability and large bearing capacitywhich reduced the settlement caused by compression of theQuaternary sand and soil layere strength of the backfilledrock mass and the backfilling material in the gob areasendured the additional load given by the pile foundation sothe stability of the gob areas was achieved

423 Residual Deformation of the Office BuildingFoundation Combined with the grouting effect the geo-logical conditions the building load and past experiencesan integral probability method [22] was used to calculate theresidual deformation and subsidence of the surface aftergrouting and the relevant parameters are shown in Table 7e contour line of the residual surface subsidence and theslope in the area where the office building was located areshown in Figure 10 Results showed that the maximumsurface subsidence value was 58mm and the maximumslope was 042mmm both of which are less than thepermissible subsoil deformation of a high-rise building (thepermissible subsidence was 200mm and the permissible

slope was 2mmm as taken from [21]) us constructionof the office building was made feasible

Owing to the detection and analysis of the groutingeffect the cavities and fractures of the bedrock were betterfilled and the force of the rock was changed from two-dimensional to three-dimensional which enhanced theoverall strength of the rock mass Meanwhile the stability ofthe foundation was effectively enhanced by constructing pilefoundation Since the residual deformation and subsidenceof the office building after grouting met the design re-quirements it became feasible to construct the officebuilding above the old gob areas

43 Monitoring Subsidence of the Office Building To acquirethe deformation of the office building timely during con-struction the subsidence of the building was monitored byan electronic level e actual boundary location of the officebuilding is shown in Figure 11 and twenty-two monitoringpoints were set in the buildingrsquos walls e monitoring pointnumbers are shown in Figure 11

Depth(m) N

947 973 998

1003978952

957 983 1008

E S W N N E S W N N E S W N

Figure 9 Images of the J1 detection borehole

Table 7 Parameters of surface movement after grouting

Calculated parameters Construction siteSubsidence factor 0025Main effecting angle tangent 16Displacement factor 030Mining affects the propagation angle 85Inflection point offset 0

8 Advances in Civil Engineering

e monitoring period of 930 days (from October 262012 to May 13 2015) was divided into four stages duringwhich 18 times of monitoring were conducted In stage 1(from day 0 to day 60) the building was constructed from 7floors to 17 floors so the load given by the office buildingincreased faster in this stage In stage 2 (from day 60 to day360) the building was capped and the walls were completede load increase in this stage was limited and some of themonitoring points were damaged by the construction Instage 3 (from day 360 to day 720) the whole building wascompleted and the indoor and outdoor renovation wascarried out In stage 4 (from day 720 to day 930) the buildingwas ready for use erefore the load in stage 3 and 4 wasalmost unchanged and stable

Because some of the monitoring points were damagedparts of the monitoring data were missing erefore twelvepoints (W1 W4 W6 W8 W9 W11 E1 E4 E6 E8 E9 andE11 points) were selected because their data were morecomplete and their locations were closer to the junction andmiddle of the boundary and the cumulative subsidence datawere recorded (Figure 12)

From Figure 12 it was found that all the subsidencevalues of the monitoring points increased rapidly in stage 1which might be caused by the increase of the load and therapid compression settlement of the stratum In this stagethe maximum subsidence value of point W9 was 85mmwith a sinking speed of 0142mmday e maximum slopeof points W1 and W2 was 0492mmm In stage 2 thesubsidence values changed irregularly and the subsidencevalues of some monitoring points were even negative in-dicating that the altitude of these monitoring points wereenhanced As all the monitoring points were set in the wallsthis phenomenon might be resulted from the artificialdisturbance to these monitoring points during the con-struction process of the building walls In stages 3 and 4 thesubsidence values were continuously increased but thespeeds were slowed down obviously indicating the slowcompression settlement of the strata under the stable load Inthese two stages the maximum subsidence and sinkingspeed values from point E6 were about 5mm and0009mmday respectively Comparing stage 1 with stages 3and 4 it can be seen that the subsidence values increased

rapidly with increasing load However with the increase ofthe subsidence accumulation and the slowdown of theapplied load the speed of the foundation subsidencedropped Combining Figure 11 with Figure 12 it can beseen that the subsidence values of those points located closeto the center of the old gob areas (eg points E4 and E6)were more than the points near the pillars (eg points W1and E1) In this way uneven settlement was generated andthe maximum difference of the value from points W1 andW4 was 104mm In the whole subsidence period therewas still residual subsidence because of the unfilled frac-tures in the strata Among the 22 monitoring points themaximum cumulative subsidence value was 153mm frompoint E4 and the maximum slope was 0765mmm frompoints W1 and W2 However compared with the per-missible subsoil subsidence (200mm) and permissiblesubsoil slope (2mmm) the maximum subsidence andslope were far less than the permissible values e officebuilding was built successfully after grouting (a photographof building is shown in Figure 13) cracking or otherdamages during construction did not occur us thestability of the foundation was enhanced greatly by the

4543

4147

4951

5355

57

5553

51

5759

Office building

(a)

05

03

010

3

01

01

Office building

(b)

Figure 10 Map of residual surface subsidence and slope contours in the area where the office building was located (a) map of residualsurface subsidence contours unit as mm (b) map of residual slope contours unit as mmm

W6W7 W8 E8 E7

E6

E5

E4

E1E2E13

E11E10

E9W9

W10

W11

W1W2W3

W4

W5

574 gob

572 gob

576 gob

Monitoring points

Figure 11 Location of the building and the monitoring points

Advances in Civil Engineering 9

grouting reinforcement which proved that the groutingreinforcement of the office building can be adopted forother large buildings constructed over old gob areas

5 Conclusions

According to the observed results from borehole explorationand the TV imaging test all 7 exploration boreholes incurredwind inhalation or drill felling e bedrock chosen for thebuilding construction had been broken and serious frac-tures had developed above the old gob areas us thestability of the gob areas was poor

e depth affected by the load (caused by the officebuilding) was 85m and the largest height of the fracturezone induced by mining was 214m And the shallowestburial depth of the No 5 coal seam was 96m and thereforethe fracture zone overlapped with the areas affected by theload of which the stability would be affected by additionalstress applied Moreover the compressive strength of thebedrock was weak so the bedrock would incur large de-formations and sedimentation when under a high load

erefore the foundation of the office building was deemedto be unstable

e grouting reinforcement measure was implementedto enhance the stability of the building foundation Aftergrouting drill felling or wind inhalation did not occur andfew water leakages were found during the process of drillingthe J1 J2 and J4 boreholes According to observationsthrough the borehole TV imaging test of the J1 J3 and J4boreholes most of the cavities and fractures were filled withslurry the filling rates were greater than 85 and therebythe effect of grouting reinforcement was obvious

According to the monitoring results of the subsidenceof the office building the maximum cumulative subsidencewas 153mm and the maximum slope was 0765mmmwhich are less than the permissible values (200mm and2mmm respectively) So it indicated that the stability ofthe foundation and old gob areas was positive and thegrouting project for the large building foundation achievedsuccess

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 there are no conflicts of interestregarding the publication of this paper

Acknowledgments

anks are due to Huaibei Mining Co for providing the insitu data and project support and Dr Zhang Huaxing for histechnical guidance Support from the National Basic Re-search Program of China (973 Program 2013CB227903) and

00 60 120 180 240 300 360 420 480

Time (days)540 600 660 720 780 840 900 960

4

8

12

Subs

iden

ce (m

m)

16

Stage 1 Stage 2 Stage 3 Stage 4

W1 pointW4 pointW6 point

E1 pointE4 pointE6 point

E8 pointE9 pointE11 point

W8 pointW9 pointW11 point

Figure 12 Subsidence values of the monitoring points

Figure 13 Photograph of the office building

10 Advances in Civil Engineering

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

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48624 tons of cement and 266027 tons of fly ash wereconsumed Detailed information regarding the groutingtime grouting amount and reason for stopping the groutingof 11 boreholes are provided in Table 5 It can be seen that allthe grouting amounts of boreholes Z3 Z4 Z7 Z14 and Z17were more than 2000 tons and the grouting time was longerthan two weeks Moreover the location of those boreholes

was close to the coal pillars or roadways indicating that thescope of the uncompacted areas and the slurry-filling areasbelow were great Emission of slurry on the ground occurredat seven boreholes and the field inspection indicated that theuncompacted areas in the old gob areas had been filled withthe slurry effectively

4 Results and Discussion

41 Detection and Analysis of the Grouting Effect

411 Drilling of Detection Boreholes Four detection bore-holes (marked J1 through J4 shown in Figure 8(a)) wereconstructed after grouting Compared with the surroundingexploration boreholes (K3 K6 and K7 boreholes) during theprocess of drilling no drill felling or wind inhalation oc-curred and the J1 and J4 boreholes no longer incurreda water leakage (Table 6) It can be concluded that thegrouting had a favorable effect on the fracture filling

412 Borehole TV Imaging Test A borehole TV imaging testwas used to image the full borehole wall to observe thefractures in the bedrock of four detection boreholes Becausethe rock had joints and fractures the surface filled withslurry was smoother than the surface of the rock In additionthe color of the slurry was grayish white and the rock waslight grayish black but the colors of the unfilled fracturesand cavities were black According to the identification andprocessing of the images the results of filling rates of de-tection boreholes were greater than 85 And TV images ofthe J1 borehole are shown in Figure 9 the areas filled in withslurry were circled with the green lines and the unfilled areas

100 120 140 160 180 200 220 240 260 280 300 320

100 120 140 160 180 200 220 240 260 280 300 320

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash2020

015

010

0

30100

100

250

60405080150 350200

400450

40

200250

250

200

150

100

506080

300

8030 40 6050

20

(a)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

150 200

250

300

450250200

300350

400

40 80 6050

100 150

40

10080

60

5040

(b)

100 120 140 160 180 200 220 240 260 280 300 320 340 360

100 120 140 160 180 200 220 240 260 280 300 320 340 360

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

5040

3025

020

0

30405060

1001508060 50

250200 400350

300 250

20015010080605040

40

(c)

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

ndash120

ndash100

ndash80

ndash60

ndash40

ndash20

10

60 2030 40 4040

200

350300250200150100806050

50

400 450

203040

40

350300

250200150100806050

250

5080(d)

Figure 6 Profile map of apparent resistivity contours of Transient Electromagnetic Geophysical Exploration (a) 1080 survey line (b) 1160survey line (c) 1240 survey line (d) 1320 survey line

Table 4 Depth affected by the load

z(m) n

p

(kPa) Ksσaz

(kPa)σz

(kPa)10 σz(kPa)

hz(m)

0 0 675 025 675 0 0 1025 130 675 0176 4509 500 50 3550 259 675 0092 2484 1000 100 6070 363 675 0058 1566 1425 1425 8072 373 675 0054 1458 1500 150 82

No 5 coal seam

Ground

Building

Areas affectedby the load(σaz gt 01σz)

Foundation surface

Additional stress(σaz = 01σz)

Hli = 214m

h z=

82m

Old gob areas

Hs=

96m

Figure 7 Relationship between the areas affected by the load andthe fractured zone

6 Advances in Civil Engineering

were circled with the red lines It can be seen that most of thecavities and fractures were filled with slurry and the closer tothe gobs the better of the grouting effect Comparing theafter grouting images results with the before grouting imagesresults (Table 2 and Figure 5) it was believed that themechanical properties of rock mass were strengthened andthe grouting project was successful

413 Water Injection Test Water injection tests were alsoconducted on a water column in the detection boreholesand the permeable rates of boreholes J1 J2 and J4 were0072 0992 and 0378 Lu respectively e permeable rateswere less than 1 Lu so the type was micropermeable andthus the cavities and rock fractures were filled in with the

slurry effectively after groutinge flushing fluid showed noor slow loss during drilling and thus the hydraulic link ofthe surrounding bedrock was poor In addition the bedrockwas able to maintain a certain water level when the waterlevel around it changed thereby avoiding the influence ofwater on the mudstone layer

42 Analysis of Other Factors to the Stability of the Foundation

421 Quaternary Sand Aquifer Observation from the ex-ploration boreholes in the old gob areas indicated that thecurrent groundwater level in the construction site was below100m No hydraulic connection existed between the Qua-ternary aquifer and the gobs and the change of the water

Table 5 Parameters of grouting boreholes

Drillingno

Grouting time Groutingamount Reason for

stopping groutingStarting Ending Cement

(t)Fly

ash (t)

Z3 Jan 14 Jan 29 6074 26352 Emitting of slurryat ground

Z6 Jan 14 Jan 15 340 1757 Emitting of slurryat ground

Z7 Jan 15 Feb 20 10685 42163 Emitting of slurryat ground

Z5 Jan 18 Jan 26 3854 18739 Emitting of slurryat ground

Z14 Feb 6 Feb 21 4998 25181 Reachinggrouting pressure

Z12 Feb 18 Feb 19 192 878 Emitting of slurryat ground

Z17 Feb 21 Mar27 8296 38544 Emitting of slurry

at ground

Z13 Feb 27 Mar 8 1390 7788 Reachinggrouting pressure

Z16 Mar 8 Mar27 1906 11110 mdash

Z4 Mar 10 Mar27 3963 25824 Emitting of slurry

at ground

Z8 Mar 22 Mar27 1055 9792 mdash

Table 6 Characteristics of the boreholes before and after grouting

Time Borehole Leakage observation Drillfelling

Windinhalation

Beforegrouting

K3995m to end all lostleakage more than

15m3hNo Yes

K61015m to end all lostleakage more than

15m3hNo Yes

K7899m to end all lostleakage more than

15m3hYes Yes

Aftergrouting

J1 No leaking No No

J2 899m to end a little lostleakage only 054m3h No No

J4 No leaking No No

A BMI N I

574 gob

572 gob

576 gob

Z15

Z16

Z17

Z1Z2

Z3(K3)

Z4Z5

Z6 (K6)

Z7(K7)

Z8

Z9Z10

Z11

Z12

Z13Z14

J4(Z18)

J1J2

J3

Detecting borehole

Office building boundaryGrouting range boundary Strike profile line

Grouting borehole

(a)

Q

φ

δ δ

φ

Building

Old gob areas

A BM N

Scope of the grouting treatment

hh j

I-I profile

(b)

Figure 8 (a) Grouting scope design and grouting boreholes ar-rangement (b) grouting scope of the I-I profile φ movement angleof Quaternary strata δ strike movement angle of bedrock QQuaternary strata h thickness of Quaternary strata hj thickness ofbedrock

Advances in Civil Engineering 7

level in the Quaternary sand aquifer was small ereforethe settlement of the soil layer caused by aquifer consoli-dation was small and the influence of the aquifer on thefoundation settlement was small

422 Pile Foundation Considering the heavy load given bythe building reinforcement measure of constructing pilefoundation was taken in addition to grouting reinforcemente depth of the pile foundation was 50m and the pilefoundation had good stability and large bearing capacitywhich reduced the settlement caused by compression of theQuaternary sand and soil layere strength of the backfilledrock mass and the backfilling material in the gob areasendured the additional load given by the pile foundation sothe stability of the gob areas was achieved

423 Residual Deformation of the Office BuildingFoundation Combined with the grouting effect the geo-logical conditions the building load and past experiencesan integral probability method [22] was used to calculate theresidual deformation and subsidence of the surface aftergrouting and the relevant parameters are shown in Table 7e contour line of the residual surface subsidence and theslope in the area where the office building was located areshown in Figure 10 Results showed that the maximumsurface subsidence value was 58mm and the maximumslope was 042mmm both of which are less than thepermissible subsoil deformation of a high-rise building (thepermissible subsidence was 200mm and the permissible

slope was 2mmm as taken from [21]) us constructionof the office building was made feasible

Owing to the detection and analysis of the groutingeffect the cavities and fractures of the bedrock were betterfilled and the force of the rock was changed from two-dimensional to three-dimensional which enhanced theoverall strength of the rock mass Meanwhile the stability ofthe foundation was effectively enhanced by constructing pilefoundation Since the residual deformation and subsidenceof the office building after grouting met the design re-quirements it became feasible to construct the officebuilding above the old gob areas

43 Monitoring Subsidence of the Office Building To acquirethe deformation of the office building timely during con-struction the subsidence of the building was monitored byan electronic level e actual boundary location of the officebuilding is shown in Figure 11 and twenty-two monitoringpoints were set in the buildingrsquos walls e monitoring pointnumbers are shown in Figure 11

Depth(m) N

947 973 998

1003978952

957 983 1008

E S W N N E S W N N E S W N

Figure 9 Images of the J1 detection borehole

Table 7 Parameters of surface movement after grouting

Calculated parameters Construction siteSubsidence factor 0025Main effecting angle tangent 16Displacement factor 030Mining affects the propagation angle 85Inflection point offset 0

8 Advances in Civil Engineering

e monitoring period of 930 days (from October 262012 to May 13 2015) was divided into four stages duringwhich 18 times of monitoring were conducted In stage 1(from day 0 to day 60) the building was constructed from 7floors to 17 floors so the load given by the office buildingincreased faster in this stage In stage 2 (from day 60 to day360) the building was capped and the walls were completede load increase in this stage was limited and some of themonitoring points were damaged by the construction Instage 3 (from day 360 to day 720) the whole building wascompleted and the indoor and outdoor renovation wascarried out In stage 4 (from day 720 to day 930) the buildingwas ready for use erefore the load in stage 3 and 4 wasalmost unchanged and stable

Because some of the monitoring points were damagedparts of the monitoring data were missing erefore twelvepoints (W1 W4 W6 W8 W9 W11 E1 E4 E6 E8 E9 andE11 points) were selected because their data were morecomplete and their locations were closer to the junction andmiddle of the boundary and the cumulative subsidence datawere recorded (Figure 12)

From Figure 12 it was found that all the subsidencevalues of the monitoring points increased rapidly in stage 1which might be caused by the increase of the load and therapid compression settlement of the stratum In this stagethe maximum subsidence value of point W9 was 85mmwith a sinking speed of 0142mmday e maximum slopeof points W1 and W2 was 0492mmm In stage 2 thesubsidence values changed irregularly and the subsidencevalues of some monitoring points were even negative in-dicating that the altitude of these monitoring points wereenhanced As all the monitoring points were set in the wallsthis phenomenon might be resulted from the artificialdisturbance to these monitoring points during the con-struction process of the building walls In stages 3 and 4 thesubsidence values were continuously increased but thespeeds were slowed down obviously indicating the slowcompression settlement of the strata under the stable load Inthese two stages the maximum subsidence and sinkingspeed values from point E6 were about 5mm and0009mmday respectively Comparing stage 1 with stages 3and 4 it can be seen that the subsidence values increased

rapidly with increasing load However with the increase ofthe subsidence accumulation and the slowdown of theapplied load the speed of the foundation subsidencedropped Combining Figure 11 with Figure 12 it can beseen that the subsidence values of those points located closeto the center of the old gob areas (eg points E4 and E6)were more than the points near the pillars (eg points W1and E1) In this way uneven settlement was generated andthe maximum difference of the value from points W1 andW4 was 104mm In the whole subsidence period therewas still residual subsidence because of the unfilled frac-tures in the strata Among the 22 monitoring points themaximum cumulative subsidence value was 153mm frompoint E4 and the maximum slope was 0765mmm frompoints W1 and W2 However compared with the per-missible subsoil subsidence (200mm) and permissiblesubsoil slope (2mmm) the maximum subsidence andslope were far less than the permissible values e officebuilding was built successfully after grouting (a photographof building is shown in Figure 13) cracking or otherdamages during construction did not occur us thestability of the foundation was enhanced greatly by the

4543

4147

4951

5355

57

5553

51

5759

Office building

(a)

05

03

010

3

01

01

Office building

(b)

Figure 10 Map of residual surface subsidence and slope contours in the area where the office building was located (a) map of residualsurface subsidence contours unit as mm (b) map of residual slope contours unit as mmm

W6W7 W8 E8 E7

E6

E5

E4

E1E2E13

E11E10

E9W9

W10

W11

W1W2W3

W4

W5

574 gob

572 gob

576 gob

Monitoring points

Figure 11 Location of the building and the monitoring points

Advances in Civil Engineering 9

grouting reinforcement which proved that the groutingreinforcement of the office building can be adopted forother large buildings constructed over old gob areas

5 Conclusions

According to the observed results from borehole explorationand the TV imaging test all 7 exploration boreholes incurredwind inhalation or drill felling e bedrock chosen for thebuilding construction had been broken and serious frac-tures had developed above the old gob areas us thestability of the gob areas was poor

e depth affected by the load (caused by the officebuilding) was 85m and the largest height of the fracturezone induced by mining was 214m And the shallowestburial depth of the No 5 coal seam was 96m and thereforethe fracture zone overlapped with the areas affected by theload of which the stability would be affected by additionalstress applied Moreover the compressive strength of thebedrock was weak so the bedrock would incur large de-formations and sedimentation when under a high load

erefore the foundation of the office building was deemedto be unstable

e grouting reinforcement measure was implementedto enhance the stability of the building foundation Aftergrouting drill felling or wind inhalation did not occur andfew water leakages were found during the process of drillingthe J1 J2 and J4 boreholes According to observationsthrough the borehole TV imaging test of the J1 J3 and J4boreholes most of the cavities and fractures were filled withslurry the filling rates were greater than 85 and therebythe effect of grouting reinforcement was obvious

According to the monitoring results of the subsidenceof the office building the maximum cumulative subsidencewas 153mm and the maximum slope was 0765mmmwhich are less than the permissible values (200mm and2mmm respectively) So it indicated that the stability ofthe foundation and old gob areas was positive and thegrouting project for the large building foundation achievedsuccess

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 there are no conflicts of interestregarding the publication of this paper

Acknowledgments

anks are due to Huaibei Mining Co for providing the insitu data and project support and Dr Zhang Huaxing for histechnical guidance Support from the National Basic Re-search Program of China (973 Program 2013CB227903) and

00 60 120 180 240 300 360 420 480

Time (days)540 600 660 720 780 840 900 960

4

8

12

Subs

iden

ce (m

m)

16

Stage 1 Stage 2 Stage 3 Stage 4

W1 pointW4 pointW6 point

E1 pointE4 pointE6 point

E8 pointE9 pointE11 point

W8 pointW9 pointW11 point

Figure 12 Subsidence values of the monitoring points

Figure 13 Photograph of the office building

10 Advances in Civil Engineering

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

RoboticsJournal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Active and Passive Electronic Components

VLSI Design

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Shock and Vibration

Hindawiwwwhindawicom Volume 2018

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawiwwwhindawicom

Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Control Scienceand Engineering

Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom

Journal ofEngineeringVolume 2018

SensorsJournal of

Hindawiwwwhindawicom Volume 2018

International Journal of

RotatingMachinery

Hindawiwwwhindawicom Volume 2018

Modelling ampSimulationin EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Navigation and Observation

International Journal of

Hindawi

wwwhindawicom Volume 2018

Advances in

Multimedia

Submit your manuscripts atwwwhindawicom

were circled with the red lines It can be seen that most of thecavities and fractures were filled with slurry and the closer tothe gobs the better of the grouting effect Comparing theafter grouting images results with the before grouting imagesresults (Table 2 and Figure 5) it was believed that themechanical properties of rock mass were strengthened andthe grouting project was successful

413 Water Injection Test Water injection tests were alsoconducted on a water column in the detection boreholesand the permeable rates of boreholes J1 J2 and J4 were0072 0992 and 0378 Lu respectively e permeable rateswere less than 1 Lu so the type was micropermeable andthus the cavities and rock fractures were filled in with the

slurry effectively after groutinge flushing fluid showed noor slow loss during drilling and thus the hydraulic link ofthe surrounding bedrock was poor In addition the bedrockwas able to maintain a certain water level when the waterlevel around it changed thereby avoiding the influence ofwater on the mudstone layer

42 Analysis of Other Factors to the Stability of the Foundation

421 Quaternary Sand Aquifer Observation from the ex-ploration boreholes in the old gob areas indicated that thecurrent groundwater level in the construction site was below100m No hydraulic connection existed between the Qua-ternary aquifer and the gobs and the change of the water

Table 5 Parameters of grouting boreholes

Drillingno

Grouting time Groutingamount Reason for

stopping groutingStarting Ending Cement

(t)Fly

ash (t)

Z3 Jan 14 Jan 29 6074 26352 Emitting of slurryat ground

Z6 Jan 14 Jan 15 340 1757 Emitting of slurryat ground

Z7 Jan 15 Feb 20 10685 42163 Emitting of slurryat ground

Z5 Jan 18 Jan 26 3854 18739 Emitting of slurryat ground

Z14 Feb 6 Feb 21 4998 25181 Reachinggrouting pressure

Z12 Feb 18 Feb 19 192 878 Emitting of slurryat ground

Z17 Feb 21 Mar27 8296 38544 Emitting of slurry

at ground

Z13 Feb 27 Mar 8 1390 7788 Reachinggrouting pressure

Z16 Mar 8 Mar27 1906 11110 mdash

Z4 Mar 10 Mar27 3963 25824 Emitting of slurry

at ground

Z8 Mar 22 Mar27 1055 9792 mdash

Table 6 Characteristics of the boreholes before and after grouting

Time Borehole Leakage observation Drillfelling

Windinhalation

Beforegrouting

K3995m to end all lostleakage more than

15m3hNo Yes

K61015m to end all lostleakage more than

15m3hNo Yes

K7899m to end all lostleakage more than

15m3hYes Yes

Aftergrouting

J1 No leaking No No

J2 899m to end a little lostleakage only 054m3h No No

J4 No leaking No No

A BMI N I

574 gob

572 gob

576 gob

Z15

Z16

Z17

Z1Z2

Z3(K3)

Z4Z5

Z6 (K6)

Z7(K7)

Z8

Z9Z10

Z11

Z12

Z13Z14

J4(Z18)

J1J2

J3

Detecting borehole

Office building boundaryGrouting range boundary Strike profile line

Grouting borehole

(a)

Q

φ

δ δ

φ

Building

Old gob areas

A BM N

Scope of the grouting treatment

hh j

I-I profile

(b)

Figure 8 (a) Grouting scope design and grouting boreholes ar-rangement (b) grouting scope of the I-I profile φ movement angleof Quaternary strata δ strike movement angle of bedrock QQuaternary strata h thickness of Quaternary strata hj thickness ofbedrock

Advances in Civil Engineering 7

level in the Quaternary sand aquifer was small ereforethe settlement of the soil layer caused by aquifer consoli-dation was small and the influence of the aquifer on thefoundation settlement was small

422 Pile Foundation Considering the heavy load given bythe building reinforcement measure of constructing pilefoundation was taken in addition to grouting reinforcemente depth of the pile foundation was 50m and the pilefoundation had good stability and large bearing capacitywhich reduced the settlement caused by compression of theQuaternary sand and soil layere strength of the backfilledrock mass and the backfilling material in the gob areasendured the additional load given by the pile foundation sothe stability of the gob areas was achieved

423 Residual Deformation of the Office BuildingFoundation Combined with the grouting effect the geo-logical conditions the building load and past experiencesan integral probability method [22] was used to calculate theresidual deformation and subsidence of the surface aftergrouting and the relevant parameters are shown in Table 7e contour line of the residual surface subsidence and theslope in the area where the office building was located areshown in Figure 10 Results showed that the maximumsurface subsidence value was 58mm and the maximumslope was 042mmm both of which are less than thepermissible subsoil deformation of a high-rise building (thepermissible subsidence was 200mm and the permissible

slope was 2mmm as taken from [21]) us constructionof the office building was made feasible

Owing to the detection and analysis of the groutingeffect the cavities and fractures of the bedrock were betterfilled and the force of the rock was changed from two-dimensional to three-dimensional which enhanced theoverall strength of the rock mass Meanwhile the stability ofthe foundation was effectively enhanced by constructing pilefoundation Since the residual deformation and subsidenceof the office building after grouting met the design re-quirements it became feasible to construct the officebuilding above the old gob areas

43 Monitoring Subsidence of the Office Building To acquirethe deformation of the office building timely during con-struction the subsidence of the building was monitored byan electronic level e actual boundary location of the officebuilding is shown in Figure 11 and twenty-two monitoringpoints were set in the buildingrsquos walls e monitoring pointnumbers are shown in Figure 11

Depth(m) N

947 973 998

1003978952

957 983 1008

E S W N N E S W N N E S W N

Figure 9 Images of the J1 detection borehole

Table 7 Parameters of surface movement after grouting

Calculated parameters Construction siteSubsidence factor 0025Main effecting angle tangent 16Displacement factor 030Mining affects the propagation angle 85Inflection point offset 0

8 Advances in Civil Engineering

e monitoring period of 930 days (from October 262012 to May 13 2015) was divided into four stages duringwhich 18 times of monitoring were conducted In stage 1(from day 0 to day 60) the building was constructed from 7floors to 17 floors so the load given by the office buildingincreased faster in this stage In stage 2 (from day 60 to day360) the building was capped and the walls were completede load increase in this stage was limited and some of themonitoring points were damaged by the construction Instage 3 (from day 360 to day 720) the whole building wascompleted and the indoor and outdoor renovation wascarried out In stage 4 (from day 720 to day 930) the buildingwas ready for use erefore the load in stage 3 and 4 wasalmost unchanged and stable

Because some of the monitoring points were damagedparts of the monitoring data were missing erefore twelvepoints (W1 W4 W6 W8 W9 W11 E1 E4 E6 E8 E9 andE11 points) were selected because their data were morecomplete and their locations were closer to the junction andmiddle of the boundary and the cumulative subsidence datawere recorded (Figure 12)

From Figure 12 it was found that all the subsidencevalues of the monitoring points increased rapidly in stage 1which might be caused by the increase of the load and therapid compression settlement of the stratum In this stagethe maximum subsidence value of point W9 was 85mmwith a sinking speed of 0142mmday e maximum slopeof points W1 and W2 was 0492mmm In stage 2 thesubsidence values changed irregularly and the subsidencevalues of some monitoring points were even negative in-dicating that the altitude of these monitoring points wereenhanced As all the monitoring points were set in the wallsthis phenomenon might be resulted from the artificialdisturbance to these monitoring points during the con-struction process of the building walls In stages 3 and 4 thesubsidence values were continuously increased but thespeeds were slowed down obviously indicating the slowcompression settlement of the strata under the stable load Inthese two stages the maximum subsidence and sinkingspeed values from point E6 were about 5mm and0009mmday respectively Comparing stage 1 with stages 3and 4 it can be seen that the subsidence values increased

rapidly with increasing load However with the increase ofthe subsidence accumulation and the slowdown of theapplied load the speed of the foundation subsidencedropped Combining Figure 11 with Figure 12 it can beseen that the subsidence values of those points located closeto the center of the old gob areas (eg points E4 and E6)were more than the points near the pillars (eg points W1and E1) In this way uneven settlement was generated andthe maximum difference of the value from points W1 andW4 was 104mm In the whole subsidence period therewas still residual subsidence because of the unfilled frac-tures in the strata Among the 22 monitoring points themaximum cumulative subsidence value was 153mm frompoint E4 and the maximum slope was 0765mmm frompoints W1 and W2 However compared with the per-missible subsoil subsidence (200mm) and permissiblesubsoil slope (2mmm) the maximum subsidence andslope were far less than the permissible values e officebuilding was built successfully after grouting (a photographof building is shown in Figure 13) cracking or otherdamages during construction did not occur us thestability of the foundation was enhanced greatly by the

4543

4147

4951

5355

57

5553

51

5759

Office building

(a)

05

03

010

3

01

01

Office building

(b)

Figure 10 Map of residual surface subsidence and slope contours in the area where the office building was located (a) map of residualsurface subsidence contours unit as mm (b) map of residual slope contours unit as mmm

W6W7 W8 E8 E7

E6

E5

E4

E1E2E13

E11E10

E9W9

W10

W11

W1W2W3

W4

W5

574 gob

572 gob

576 gob

Monitoring points

Figure 11 Location of the building and the monitoring points

Advances in Civil Engineering 9

grouting reinforcement which proved that the groutingreinforcement of the office building can be adopted forother large buildings constructed over old gob areas

5 Conclusions

According to the observed results from borehole explorationand the TV imaging test all 7 exploration boreholes incurredwind inhalation or drill felling e bedrock chosen for thebuilding construction had been broken and serious frac-tures had developed above the old gob areas us thestability of the gob areas was poor

e depth affected by the load (caused by the officebuilding) was 85m and the largest height of the fracturezone induced by mining was 214m And the shallowestburial depth of the No 5 coal seam was 96m and thereforethe fracture zone overlapped with the areas affected by theload of which the stability would be affected by additionalstress applied Moreover the compressive strength of thebedrock was weak so the bedrock would incur large de-formations and sedimentation when under a high load

erefore the foundation of the office building was deemedto be unstable

e grouting reinforcement measure was implementedto enhance the stability of the building foundation Aftergrouting drill felling or wind inhalation did not occur andfew water leakages were found during the process of drillingthe J1 J2 and J4 boreholes According to observationsthrough the borehole TV imaging test of the J1 J3 and J4boreholes most of the cavities and fractures were filled withslurry the filling rates were greater than 85 and therebythe effect of grouting reinforcement was obvious

According to the monitoring results of the subsidenceof the office building the maximum cumulative subsidencewas 153mm and the maximum slope was 0765mmmwhich are less than the permissible values (200mm and2mmm respectively) So it indicated that the stability ofthe foundation and old gob areas was positive and thegrouting project for the large building foundation achievedsuccess

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 there are no conflicts of interestregarding the publication of this paper

Acknowledgments

anks are due to Huaibei Mining Co for providing the insitu data and project support and Dr Zhang Huaxing for histechnical guidance Support from the National Basic Re-search Program of China (973 Program 2013CB227903) and

00 60 120 180 240 300 360 420 480

Time (days)540 600 660 720 780 840 900 960

4

8

12

Subs

iden

ce (m

m)

16

Stage 1 Stage 2 Stage 3 Stage 4

W1 pointW4 pointW6 point

E1 pointE4 pointE6 point

E8 pointE9 pointE11 point

W8 pointW9 pointW11 point

Figure 12 Subsidence values of the monitoring points

Figure 13 Photograph of the office building

10 Advances in Civil Engineering

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

RoboticsJournal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Active and Passive Electronic Components

VLSI Design

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Shock and Vibration

Hindawiwwwhindawicom Volume 2018

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawiwwwhindawicom

Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Control Scienceand Engineering

Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom

Journal ofEngineeringVolume 2018

SensorsJournal of

Hindawiwwwhindawicom Volume 2018

International Journal of

RotatingMachinery

Hindawiwwwhindawicom Volume 2018

Modelling ampSimulationin EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Navigation and Observation

International Journal of

Hindawi

wwwhindawicom Volume 2018

Advances in

Multimedia

Submit your manuscripts atwwwhindawicom

level in the Quaternary sand aquifer was small ereforethe settlement of the soil layer caused by aquifer consoli-dation was small and the influence of the aquifer on thefoundation settlement was small

422 Pile Foundation Considering the heavy load given bythe building reinforcement measure of constructing pilefoundation was taken in addition to grouting reinforcemente depth of the pile foundation was 50m and the pilefoundation had good stability and large bearing capacitywhich reduced the settlement caused by compression of theQuaternary sand and soil layere strength of the backfilledrock mass and the backfilling material in the gob areasendured the additional load given by the pile foundation sothe stability of the gob areas was achieved

423 Residual Deformation of the Office BuildingFoundation Combined with the grouting effect the geo-logical conditions the building load and past experiencesan integral probability method [22] was used to calculate theresidual deformation and subsidence of the surface aftergrouting and the relevant parameters are shown in Table 7e contour line of the residual surface subsidence and theslope in the area where the office building was located areshown in Figure 10 Results showed that the maximumsurface subsidence value was 58mm and the maximumslope was 042mmm both of which are less than thepermissible subsoil deformation of a high-rise building (thepermissible subsidence was 200mm and the permissible

slope was 2mmm as taken from [21]) us constructionof the office building was made feasible

Owing to the detection and analysis of the groutingeffect the cavities and fractures of the bedrock were betterfilled and the force of the rock was changed from two-dimensional to three-dimensional which enhanced theoverall strength of the rock mass Meanwhile the stability ofthe foundation was effectively enhanced by constructing pilefoundation Since the residual deformation and subsidenceof the office building after grouting met the design re-quirements it became feasible to construct the officebuilding above the old gob areas

43 Monitoring Subsidence of the Office Building To acquirethe deformation of the office building timely during con-struction the subsidence of the building was monitored byan electronic level e actual boundary location of the officebuilding is shown in Figure 11 and twenty-two monitoringpoints were set in the buildingrsquos walls e monitoring pointnumbers are shown in Figure 11

Depth(m) N

947 973 998

1003978952

957 983 1008

E S W N N E S W N N E S W N

Figure 9 Images of the J1 detection borehole

Table 7 Parameters of surface movement after grouting

Calculated parameters Construction siteSubsidence factor 0025Main effecting angle tangent 16Displacement factor 030Mining affects the propagation angle 85Inflection point offset 0

8 Advances in Civil Engineering

e monitoring period of 930 days (from October 262012 to May 13 2015) was divided into four stages duringwhich 18 times of monitoring were conducted In stage 1(from day 0 to day 60) the building was constructed from 7floors to 17 floors so the load given by the office buildingincreased faster in this stage In stage 2 (from day 60 to day360) the building was capped and the walls were completede load increase in this stage was limited and some of themonitoring points were damaged by the construction Instage 3 (from day 360 to day 720) the whole building wascompleted and the indoor and outdoor renovation wascarried out In stage 4 (from day 720 to day 930) the buildingwas ready for use erefore the load in stage 3 and 4 wasalmost unchanged and stable

Because some of the monitoring points were damagedparts of the monitoring data were missing erefore twelvepoints (W1 W4 W6 W8 W9 W11 E1 E4 E6 E8 E9 andE11 points) were selected because their data were morecomplete and their locations were closer to the junction andmiddle of the boundary and the cumulative subsidence datawere recorded (Figure 12)

From Figure 12 it was found that all the subsidencevalues of the monitoring points increased rapidly in stage 1which might be caused by the increase of the load and therapid compression settlement of the stratum In this stagethe maximum subsidence value of point W9 was 85mmwith a sinking speed of 0142mmday e maximum slopeof points W1 and W2 was 0492mmm In stage 2 thesubsidence values changed irregularly and the subsidencevalues of some monitoring points were even negative in-dicating that the altitude of these monitoring points wereenhanced As all the monitoring points were set in the wallsthis phenomenon might be resulted from the artificialdisturbance to these monitoring points during the con-struction process of the building walls In stages 3 and 4 thesubsidence values were continuously increased but thespeeds were slowed down obviously indicating the slowcompression settlement of the strata under the stable load Inthese two stages the maximum subsidence and sinkingspeed values from point E6 were about 5mm and0009mmday respectively Comparing stage 1 with stages 3and 4 it can be seen that the subsidence values increased

rapidly with increasing load However with the increase ofthe subsidence accumulation and the slowdown of theapplied load the speed of the foundation subsidencedropped Combining Figure 11 with Figure 12 it can beseen that the subsidence values of those points located closeto the center of the old gob areas (eg points E4 and E6)were more than the points near the pillars (eg points W1and E1) In this way uneven settlement was generated andthe maximum difference of the value from points W1 andW4 was 104mm In the whole subsidence period therewas still residual subsidence because of the unfilled frac-tures in the strata Among the 22 monitoring points themaximum cumulative subsidence value was 153mm frompoint E4 and the maximum slope was 0765mmm frompoints W1 and W2 However compared with the per-missible subsoil subsidence (200mm) and permissiblesubsoil slope (2mmm) the maximum subsidence andslope were far less than the permissible values e officebuilding was built successfully after grouting (a photographof building is shown in Figure 13) cracking or otherdamages during construction did not occur us thestability of the foundation was enhanced greatly by the

4543

4147

4951

5355

57

5553

51

5759

Office building

(a)

05

03

010

3

01

01

Office building

(b)

Figure 10 Map of residual surface subsidence and slope contours in the area where the office building was located (a) map of residualsurface subsidence contours unit as mm (b) map of residual slope contours unit as mmm

W6W7 W8 E8 E7

E6

E5

E4

E1E2E13

E11E10

E9W9

W10

W11

W1W2W3

W4

W5

574 gob

572 gob

576 gob

Monitoring points

Figure 11 Location of the building and the monitoring points

Advances in Civil Engineering 9

grouting reinforcement which proved that the groutingreinforcement of the office building can be adopted forother large buildings constructed over old gob areas

5 Conclusions

According to the observed results from borehole explorationand the TV imaging test all 7 exploration boreholes incurredwind inhalation or drill felling e bedrock chosen for thebuilding construction had been broken and serious frac-tures had developed above the old gob areas us thestability of the gob areas was poor

e depth affected by the load (caused by the officebuilding) was 85m and the largest height of the fracturezone induced by mining was 214m And the shallowestburial depth of the No 5 coal seam was 96m and thereforethe fracture zone overlapped with the areas affected by theload of which the stability would be affected by additionalstress applied Moreover the compressive strength of thebedrock was weak so the bedrock would incur large de-formations and sedimentation when under a high load

erefore the foundation of the office building was deemedto be unstable

e grouting reinforcement measure was implementedto enhance the stability of the building foundation Aftergrouting drill felling or wind inhalation did not occur andfew water leakages were found during the process of drillingthe J1 J2 and J4 boreholes According to observationsthrough the borehole TV imaging test of the J1 J3 and J4boreholes most of the cavities and fractures were filled withslurry the filling rates were greater than 85 and therebythe effect of grouting reinforcement was obvious

According to the monitoring results of the subsidenceof the office building the maximum cumulative subsidencewas 153mm and the maximum slope was 0765mmmwhich are less than the permissible values (200mm and2mmm respectively) So it indicated that the stability ofthe foundation and old gob areas was positive and thegrouting project for the large building foundation achievedsuccess

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 there are no conflicts of interestregarding the publication of this paper

Acknowledgments

anks are due to Huaibei Mining Co for providing the insitu data and project support and Dr Zhang Huaxing for histechnical guidance Support from the National Basic Re-search Program of China (973 Program 2013CB227903) and

00 60 120 180 240 300 360 420 480

Time (days)540 600 660 720 780 840 900 960

4

8

12

Subs

iden

ce (m

m)

16

Stage 1 Stage 2 Stage 3 Stage 4

W1 pointW4 pointW6 point

E1 pointE4 pointE6 point

E8 pointE9 pointE11 point

W8 pointW9 pointW11 point

Figure 12 Subsidence values of the monitoring points

Figure 13 Photograph of the office building

10 Advances in Civil Engineering

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

RoboticsJournal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Active and Passive Electronic Components

VLSI Design

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Shock and Vibration

Hindawiwwwhindawicom Volume 2018

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawiwwwhindawicom

Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Control Scienceand Engineering

Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom

Journal ofEngineeringVolume 2018

SensorsJournal of

Hindawiwwwhindawicom Volume 2018

International Journal of

RotatingMachinery

Hindawiwwwhindawicom Volume 2018

Modelling ampSimulationin EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Navigation and Observation

International Journal of

Hindawi

wwwhindawicom Volume 2018

Advances in

Multimedia

Submit your manuscripts atwwwhindawicom

e monitoring period of 930 days (from October 262012 to May 13 2015) was divided into four stages duringwhich 18 times of monitoring were conducted In stage 1(from day 0 to day 60) the building was constructed from 7floors to 17 floors so the load given by the office buildingincreased faster in this stage In stage 2 (from day 60 to day360) the building was capped and the walls were completede load increase in this stage was limited and some of themonitoring points were damaged by the construction Instage 3 (from day 360 to day 720) the whole building wascompleted and the indoor and outdoor renovation wascarried out In stage 4 (from day 720 to day 930) the buildingwas ready for use erefore the load in stage 3 and 4 wasalmost unchanged and stable

Because some of the monitoring points were damagedparts of the monitoring data were missing erefore twelvepoints (W1 W4 W6 W8 W9 W11 E1 E4 E6 E8 E9 andE11 points) were selected because their data were morecomplete and their locations were closer to the junction andmiddle of the boundary and the cumulative subsidence datawere recorded (Figure 12)

From Figure 12 it was found that all the subsidencevalues of the monitoring points increased rapidly in stage 1which might be caused by the increase of the load and therapid compression settlement of the stratum In this stagethe maximum subsidence value of point W9 was 85mmwith a sinking speed of 0142mmday e maximum slopeof points W1 and W2 was 0492mmm In stage 2 thesubsidence values changed irregularly and the subsidencevalues of some monitoring points were even negative in-dicating that the altitude of these monitoring points wereenhanced As all the monitoring points were set in the wallsthis phenomenon might be resulted from the artificialdisturbance to these monitoring points during the con-struction process of the building walls In stages 3 and 4 thesubsidence values were continuously increased but thespeeds were slowed down obviously indicating the slowcompression settlement of the strata under the stable load Inthese two stages the maximum subsidence and sinkingspeed values from point E6 were about 5mm and0009mmday respectively Comparing stage 1 with stages 3and 4 it can be seen that the subsidence values increased

rapidly with increasing load However with the increase ofthe subsidence accumulation and the slowdown of theapplied load the speed of the foundation subsidencedropped Combining Figure 11 with Figure 12 it can beseen that the subsidence values of those points located closeto the center of the old gob areas (eg points E4 and E6)were more than the points near the pillars (eg points W1and E1) In this way uneven settlement was generated andthe maximum difference of the value from points W1 andW4 was 104mm In the whole subsidence period therewas still residual subsidence because of the unfilled frac-tures in the strata Among the 22 monitoring points themaximum cumulative subsidence value was 153mm frompoint E4 and the maximum slope was 0765mmm frompoints W1 and W2 However compared with the per-missible subsoil subsidence (200mm) and permissiblesubsoil slope (2mmm) the maximum subsidence andslope were far less than the permissible values e officebuilding was built successfully after grouting (a photographof building is shown in Figure 13) cracking or otherdamages during construction did not occur us thestability of the foundation was enhanced greatly by the

4543

4147

4951

5355

57

5553

51

5759

Office building

(a)

05

03

010

3

01

01

Office building

(b)

Figure 10 Map of residual surface subsidence and slope contours in the area where the office building was located (a) map of residualsurface subsidence contours unit as mm (b) map of residual slope contours unit as mmm

W6W7 W8 E8 E7

E6

E5

E4

E1E2E13

E11E10

E9W9

W10

W11

W1W2W3

W4

W5

574 gob

572 gob

576 gob

Monitoring points

Figure 11 Location of the building and the monitoring points

Advances in Civil Engineering 9

grouting reinforcement which proved that the groutingreinforcement of the office building can be adopted forother large buildings constructed over old gob areas

5 Conclusions

According to the observed results from borehole explorationand the TV imaging test all 7 exploration boreholes incurredwind inhalation or drill felling e bedrock chosen for thebuilding construction had been broken and serious frac-tures had developed above the old gob areas us thestability of the gob areas was poor

e depth affected by the load (caused by the officebuilding) was 85m and the largest height of the fracturezone induced by mining was 214m And the shallowestburial depth of the No 5 coal seam was 96m and thereforethe fracture zone overlapped with the areas affected by theload of which the stability would be affected by additionalstress applied Moreover the compressive strength of thebedrock was weak so the bedrock would incur large de-formations and sedimentation when under a high load

erefore the foundation of the office building was deemedto be unstable

e grouting reinforcement measure was implementedto enhance the stability of the building foundation Aftergrouting drill felling or wind inhalation did not occur andfew water leakages were found during the process of drillingthe J1 J2 and J4 boreholes According to observationsthrough the borehole TV imaging test of the J1 J3 and J4boreholes most of the cavities and fractures were filled withslurry the filling rates were greater than 85 and therebythe effect of grouting reinforcement was obvious

According to the monitoring results of the subsidenceof the office building the maximum cumulative subsidencewas 153mm and the maximum slope was 0765mmmwhich are less than the permissible values (200mm and2mmm respectively) So it indicated that the stability ofthe foundation and old gob areas was positive and thegrouting project for the large building foundation achievedsuccess

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 there are no conflicts of interestregarding the publication of this paper

Acknowledgments

anks are due to Huaibei Mining Co for providing the insitu data and project support and Dr Zhang Huaxing for histechnical guidance Support from the National Basic Re-search Program of China (973 Program 2013CB227903) and

00 60 120 180 240 300 360 420 480

Time (days)540 600 660 720 780 840 900 960

4

8

12

Subs

iden

ce (m

m)

16

Stage 1 Stage 2 Stage 3 Stage 4

W1 pointW4 pointW6 point

E1 pointE4 pointE6 point

E8 pointE9 pointE11 point

W8 pointW9 pointW11 point

Figure 12 Subsidence values of the monitoring points

Figure 13 Photograph of the office building

10 Advances in Civil Engineering

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

RoboticsJournal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Active and Passive Electronic Components

VLSI Design

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Shock and Vibration

Hindawiwwwhindawicom Volume 2018

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawiwwwhindawicom

Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Control Scienceand Engineering

Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom

Journal ofEngineeringVolume 2018

SensorsJournal of

Hindawiwwwhindawicom Volume 2018

International Journal of

RotatingMachinery

Hindawiwwwhindawicom Volume 2018

Modelling ampSimulationin EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Navigation and Observation

International Journal of

Hindawi

wwwhindawicom Volume 2018

Advances in

Multimedia

Submit your manuscripts atwwwhindawicom

grouting reinforcement which proved that the groutingreinforcement of the office building can be adopted forother large buildings constructed over old gob areas

5 Conclusions

According to the observed results from borehole explorationand the TV imaging test all 7 exploration boreholes incurredwind inhalation or drill felling e bedrock chosen for thebuilding construction had been broken and serious frac-tures had developed above the old gob areas us thestability of the gob areas was poor

e depth affected by the load (caused by the officebuilding) was 85m and the largest height of the fracturezone induced by mining was 214m And the shallowestburial depth of the No 5 coal seam was 96m and thereforethe fracture zone overlapped with the areas affected by theload of which the stability would be affected by additionalstress applied Moreover the compressive strength of thebedrock was weak so the bedrock would incur large de-formations and sedimentation when under a high load

erefore the foundation of the office building was deemedto be unstable

e grouting reinforcement measure was implementedto enhance the stability of the building foundation Aftergrouting drill felling or wind inhalation did not occur andfew water leakages were found during the process of drillingthe J1 J2 and J4 boreholes According to observationsthrough the borehole TV imaging test of the J1 J3 and J4boreholes most of the cavities and fractures were filled withslurry the filling rates were greater than 85 and therebythe effect of grouting reinforcement was obvious

According to the monitoring results of the subsidenceof the office building the maximum cumulative subsidencewas 153mm and the maximum slope was 0765mmmwhich are less than the permissible values (200mm and2mmm respectively) So it indicated that the stability ofthe foundation and old gob areas was positive and thegrouting project for the large building foundation achievedsuccess

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 there are no conflicts of interestregarding the publication of this paper

Acknowledgments

anks are due to Huaibei Mining Co for providing the insitu data and project support and Dr Zhang Huaxing for histechnical guidance Support from the National Basic Re-search Program of China (973 Program 2013CB227903) and

00 60 120 180 240 300 360 420 480

Time (days)540 600 660 720 780 840 900 960

4

8

12

Subs

iden

ce (m

m)

16

Stage 1 Stage 2 Stage 3 Stage 4

W1 pointW4 pointW6 point

E1 pointE4 pointE6 point

E8 pointE9 pointE11 point

W8 pointW9 pointW11 point

Figure 12 Subsidence values of the monitoring points

Figure 13 Photograph of the office building

10 Advances in Civil Engineering

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

RoboticsJournal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Active and Passive Electronic Components

VLSI Design

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Shock and Vibration

Hindawiwwwhindawicom Volume 2018

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawiwwwhindawicom

Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Control Scienceand Engineering

Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom

Journal ofEngineeringVolume 2018

SensorsJournal of

Hindawiwwwhindawicom Volume 2018

International Journal of

RotatingMachinery

Hindawiwwwhindawicom Volume 2018

Modelling ampSimulationin EngineeringHindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Navigation and Observation

International Journal of

Hindawi

wwwhindawicom Volume 2018

Advances in

Multimedia

Submit your manuscripts atwwwhindawicom

the Project Foundation of Hebei State Key Laboratory ofMine Disaster Prevention (no KJZH2017K04) is alsogratefully acknowledged

References

[1] R J Sweigard and R V Rammani ldquoSite planning processapplication to land use potential evaluation for mined landrdquoMining Engineering vol 6 pp 427ndash432 1986

[2] T P William ldquoReclamation of surface-mined landrdquo OhioJournal of Science vol 75 no 6 pp 298ndash304 1975

[3] Y Q Tan ldquoUtilization in control of coal mining areas andreconstruction of squatter settlementrdquo Coal Mining Tech-nology vol 13 no 2 pp 1ndash5 2008 in Chinese

[4] C X Xiong and H C Liang ldquoStability analysis of the buildingfoundation over goaf areardquo Journal of Mining and SafetyEngineering vol 27 no 1 pp 100ndash105 2008 in Chinese

[5] R W Bruhm ldquoSubsidence over abandoned mines in thePittsburgh coalbedrdquo in Proceedings of Conference Held at theUniversity of Wales Institute of Science and TechnologyCardiff UK July 1977

[6] P R Healy and J M Head Construction over AbandonedMine Workings Construction Industry Research and In-formation Association (CIRIA) London UK 1984

[7] Q Yang Y H Ke D Y Zhang et al ldquoMulti-scale Analysis ofthe relationship between land subsidence and buildings a casestudy in an eastern Beijing Urban area using the PS-InSARtechniquerdquo Remote Sensing vol 10 no 7 pp 1006ndash10252018

[8] Y H Teng Z X Tang S H Li et al ldquoEvaluation of foun-dation stability in coal mine subsidence area and deformationresistance technologyrdquo in Proceedings of International Con-ference on Geoinformatics pp 1ndash4 Buffalo NY USA August2017

[9] W J Guo and Y Y Wang ldquoStability evaluation of con-structing large-scale building-to ftabove mine goafsrdquo Rockand Soil Mechanics vol 25 pp 57ndash59 2004

[10] I A Turchaninov and M A Iofis Principles of Rock Me-chanics Terrascape Inc Press Rockville USA 1977

[11] V Palchik ldquoAnalytical and empirical prognosis of rock fo-liation in rock massesrdquo Journal of Coal Ukraine vol 7pp 45-46 1989

[12] M Karmis T Triplett C Haycocks and G GoodmanldquoMining subsidence and its prediction in an Appalachiancoalfieldrdquo in Proceedings of 24th US Symposium on RockMechanics pp 665ndash675 Balkema Seattle WA USA June1983

[13] B N Whittaker and D J Reddish Subsidence OccurrencePrediction and Control Elsevier Elsevier Science Press NewYork NY USA 1989

[14] H C Jung S W Kim and H S Jung ldquoSatellite observation ofcoal mining subsidence by persistent scatterer analysisrdquoEngineering Geology vol 92 no 1-2 pp 1ndash13 2007

[15] Y Gueguen B Deffontaines and B Fruneau ldquoMonitoringresidual mining subsidence of NordPas-de-Calais coal basinfrom differential and Persistent Scatterer Interferometry(Northern France)rdquo Journal of Applied Geophysics vol 69no 1 pp 24ndash34 2009

[16] Y H Teng and J Y Zhang ldquoEvaluation on stability ofbuilding foundation over goafsrdquo Journal of China Coal So-ciety vol 22 no 5 pp 504ndash508 1997 in Chinese

[17] F M Li S Z Li and G L Bai ldquoResearch on influence ofbuildings load on basement stability over goafrdquo Coal miningTechnology vol 15 no 3 pp 5ndash7 2006 in Chinese

[18] J Y Zhang ldquoe laws of overlying strata influenced by newlyincreased load on the surface above worked-out areardquo Journalof China Coal Society vol 33 no 2 pp 166ndash170 2008 inChinese

[19] J Y Zhang ldquoFuzzy comprehensive evaluation method of thefoundation stability of new-buildings above worked-outareasrdquo Journal of University of Science and Technology Bei-jing vol 31 no 11 pp 1368ndash1372 2009 in Chinese

[20] C J Ding and J L Wang ldquoUsing artificial neural network toassess the stability of goaf foundationrdquo Journal of Mining andSafety Engineering vol 26 no 2 pp 208ndash211 2009 inChinese

[21] Ministry of Construction of the Peoplersquos Republic of ChinaCode for Design of Building Foundation China Building In-dustry Press Beijing China 2002 in Chinese

[22] State Bureau of Coal Industry Regulations of Coal Pillar Setand Mining of Building Water Body Railway and Main WellLane China Coal Industry Publishing House Beijing China2000 in Chinese

Advances in Civil Engineering 11

International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

RoboticsJournal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Active and Passive Electronic Components

VLSI Design

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Shock and Vibration

Hindawiwwwhindawicom Volume 2018

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom Volume 2018

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawiwwwhindawicom

Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Control Scienceand Engineering

Journal of

Hindawiwwwhindawicom Volume 2018

Hindawiwwwhindawicom

Journal ofEngineeringVolume 2018

SensorsJournal of

Hindawiwwwhindawicom Volume 2018

International Journal of

RotatingMachinery

Hindawiwwwhindawicom Volume 2018

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