Research ArticleExperiment on Mine Ground Pressure of Stiff Coal-PillarEntry Retaining under the Activation Condition ofHard Roof

Wen-long Shen 12 Wen-bing Guo 12 Hua Nan 12 Chun Wang 12 Yi Tan 12

and Fa-qiang Su12

1School of Energy Science and Engineering Henan Polytechnic University Jiaozuo 454000 China2Collaborative Innovation Center of Coal Work Safety of Henan Province Jiaozuo 454000 China

Correspondence should be addressed to Wen-bing Guo guowbhpueducn Hua Nan nanhuahpueducnChun Wang wangchunhpueducn and Yi Tan 517237667qqcom

Received 9 May 2018 Revised 10 July 2018 Accepted 14 August 2018 Published 18 October 2018

Academic Editor Mohsen S Masoudian

Copyright copy 2018 Wen-long Shen et al 4is 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

In mining excavation the retained entry with stiff coal pillar is situated in the strong mine ground pressure Influenced by miningabutment stress and dynamic stress (the vibration signal) induced from the hard roof activation the retained entry may besubjected to roof separation supporting body failure severe floor heave and even roof collapse Based on a 2D physical model anexperimental method with plane-stress conditions was used to simulate the mechanical behavior of the rock strata during miningIn this experiment three monitoring systems were adopted to reveal the characteristics of the strong mine ground pressure in thestiff coal-pillar entry retaining 4e results show that the hard roof undergoes bending down fracture and caving activationsuccessively until it is able to support overlying loads 4e abutment stress which is induced from the loading transfer in stiff coalpillar is larger than that in other rocks around the retained entry in amplification and overlying loads above the worked-out areahave a loading effect on the unworked-out area When the hard roof is situated in the activation state the dynamic stress isgenerated from the hard roof activation which is verified by the great saltation of acoustic emission signals 4e results of miningground pressure in the physical model can clearly illustrate themechanical behavior of the rock around the retained entry with stiffcoal pillar

1 Introduction

As a fossil energy source coal has provided enormous en-ergy for human civilization in the past and in the futureStrip mining and underground mining are the main ways tomaintain the sustainable development of coal productionSecurity maintenance of entries in underground miningrequires solving many engineering and mechanical prob-lems which is a key technology to ensure the normal op-eration of the production system [1] As the development ofthe longwall mining there are two entries on both sides ofevery longwall panel which is called the two-entry systemthroughout the world [2ndash4] Figure 1 schematically showsthe two-entry system when extracting coal from Panel 1Head entry 1 and Tail entry 2 serve Panel 1 together with

auxiliary transportation and ventilation function until thecoal is mined out in Panel 1 However Tail entry 2 facesa number of challenges which are caused by extraction suchas mining-induced stress evolution instability of supportbody roof separation and the severe floor heave From theview of mechanics the question that whether Tail entry 2 canbe retained to serve Panel 2 with stiff coal pillar needs to befurther discussed

Stage 1 is the in situ stress state of Tail entry 2 which isnot affected by the hard roof activation above the adjacentgob Stage 2 is the stress evolution state of Tail entry 2 whichis affected by the hard roof activation above the adjacent gobStage 3 is the side abutment stress state of Tail entry 2 whichis not affected by the hard roof activation above the adjacentgob and Tail entry 2 should be retained to serve Panel 2

HindawiAdvances in Civil EngineeringVolume 2018 Article ID 2629871 11 pageshttpsdoiorg10115520182629871

Coal pillar width determines the stress conditionaround the retained entry during the hard roof activationabove the gob in Panel 1 [5ndash9] Strength reduction of thecoal pillar is treated as the decreasing ratio of the pillarrsquoswidth and height [10] When the hard roof above the gobis stable in Panel 1 yield coal pillar places the retainedentry in the stress-releasing state while stiff coal pillarplaces it in the stress concentration state [11] Shabani-mashcool and Li [12] found that stresses in the stiff coalpillar fluctuate up and down during mining because ofperiodic cave-in events behind the longwall face Wanget al [13] believed that the coal bump risk of the retainedentry is enhanced significantly when the coal pillar widthincreases Bai et al [14] analyzed the roof failure mech-anism of the retained entry and determined the width ofthe coal pillar as less than 5m or more than 22m based onthe side abutment stress evolution Under the condition ofthe field monitoring Yu et al [15] found that the mining-induced abutment stress in 38m wide stiff coal pillar isaffected by the hard roof activation above the gob with theincrease of 21MPa while the consideration of the mining-induced dynamic stress in the stiff coal pillar was notinvolved Mohammadi et al [16] demonstrated that theextension of excavation-damaged zone above the retainedentry occurs as the coal pillar width decreases from 30mto 10m based on a computational geometric model Shenet al [17] concluded that the roof with weak plane for theretained entry is easily subjected to shear failure when theratio of the pillarrsquos width and height is less than 8mSeveral significant researches have great influence on thestability of the retained entry [18ndash22]

4e method of cutting hard roof to achieve thepressure relief has been widely used in the world [23ndash25]Huang et al [26] proposed a method of improving the topcoal cavability through top coal and roof hydraulicfracturing which makes the recovery ratio reaches morethan 80 under the condition of hard super-thick coalseam 4rough the physical experiment of the hydraulicfracturing for hard roof Lin et al [27] obtained that theinitial notch can effectively reduce breakdown pressureand a longer notch together with an appropriate notchangle can result in a more gradual smoother fracturereorientation path in the hard roof Han et al [28] de-termined the optimal cantilever length of the lateral

cantilever roof structure according to the deformation ofthe retained entry As the development of the hydraulicfracturing technology the hard roof weakening not onlyimproves the cavability but also decreases the abutmentstress around the worked-out area during longwall mining[29] Bai et al [30] demonstrated that hard roof treatmentresults in the lower stress concentration and smallerdeformation making it possible for safe retained entry byusing small pillar sizes based on the numerical simulationresults Besides Xia et al [31ndash33] discussed the mining-induced ground movement and deformation in tectonicstress metal mines based on case studies

In this work a 2D physical model with plane-stressconditions was established to simulate the mechanicalbehavior of the rock strata behind the working faceduring the mining process In this physical model threemonitoring systems were used to reveal the character-istics of strong mine ground pressure in stiff coal-pillarentry retaining

2 Experimental Method

21 Geological and Mining Conditions First Yangquan coalmine is located in the city of Yangquan Shanxi ProvinceChina 4e two-entry system which is employed in thelongwall top coal caving operation is approximately 2200mlong by 220m wide in every panel as shown in Figure 1 4eaverage thickness and buried depth of coal seam 15 are 65mand 600m with the dip angle of 4deg As shown in Figure 2 therock strata above coal seam 15 are limestone mudstonegroup and fine sandstone whereas rock strata below coalseam 15 are mudstone and sandstone4e south of Panel 2 isPanel 1 the retreating area 4e north of Panel 2 is Panel 3which does not have any mining activities 4e east of Panel2 is the mine boundary and there are three entries in thewest of Panel 2 4e Tail entry 2 with dimensions of 50m times

40m is arranged along the immediate roof 4e width of thestiff coal pillar is 15m

22 PhysicalModel 4e physical experiment was conductedby a physical modeling system at the State Key Laboratory ofCoal Resources and Mine Safety in China As shown inFigure 3 the modeling system consists of a servo load

Stage 1

Stiff coal pillar

Panel 1

Head entry 2

Tail entry 2

Head entry 1

Tail entry 1

Stage 2Stage 3

Panel 2

Gob

xy

z

Figure 1 Layout of two-entry system in longwall panel

2 Advances in Civil Engineering

control system a high stiff loading frame and three mon-itoring systems 4e dimension of the physical model rea-ches 25m in length 03m in width and 2m in heightUnder the geological and engineering condition of theretained entry in Panel 2 of First Yangquan coal mine therock strata of 400m long in the field were established tosimulate the mechanical behavior in Panel 1 of 220m long

the stiff coal pillar of 15m long the retained entry of 5mlong partial Panel 2 of 80m long and the boundary of 80mlong in the physical model According to the similaritytheory [34] strength density and geometry should followthe particular relationship as Equation (1) For this worksimilarity ratios of CLCρCσ Ct are determined as 160 1532448 and 1265 respectively

Lithology

Medium sandstoneSiltstoneSandy mudstoneSilty mudstoneMudstone

LimestoneCoal seam 15

Sandy mudstone

Sandy mudstone

Sandy mudstoneMudstone

Mudstone

Mudstone

Siltstone

Fine sandstone

ickness(m)

Depth(m)

Remarks

23050

10050

200180100208020

1101356520

100

479048404940

50905290547055705590567056905800593560006020

4990

Coal seamHard roof

Mudstone group

Hard roof

Hard roof100 4690

Mudstone group

Mudstone

MudstoneMudstone

Figure 2 Generalized stratigraphic column

Monitoringpoint of

displacement

Miniaturepressure

cell

Acousticemission

sensor

Loading ram

Physical model Experimental sceneServo load

control system

TS3866photogrammetric system

Acoustic emissionmonitoring system

UEILOGGERdata acquisition system

Loading frame

Figure 3 Experimental scene with physical model and monitoring systems

Advances in Civil Engineering 3

Cσ

CρCL

1

CL Lp

Lm

Cσ σpσm

Cρ ρpρm

Ct CLCL

1113968

⎧⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎩

(1)

where CL Cσ and Ct are the similarity ratios of geometrystrength and time respectively Cρ is the density simi-larity ratio between the prototype and the model Lp σpand ρp represent the dimension strength and density ofthe rock strata in the field Lm σm and ρm represent thedimension strength and density of the rock strata in themodel

23 Physical Materials As shown in Figure 2 eight ma-terials with different deformability and strength are usedto simulate the mechanical behavior of the rock strataincluding mudstone coal seam 15 limestone mudstonegroup 1 fine sandstone mudstone group 2 mediumsandstone and mudstone group 3 Physical materials aremingled with sand gypsum calcium carbonate waterand mica powder Under the condition of the uniaxialcompression test and the strength similarity ratio theratio of the material contents is determined based on theexisting results [35] For this work eight materials arepresented in Table 1 Totally 173391 kg sand 16910 kgcalcium carbonate 23449 kg gypsum and 25 kg micapowder are deserved in this model

24 Monitoring Instruments and Methods Evolution of theabutment stress acoustic emission signals and the rockstrata displacement are determined as indexes of the mineground pressure during the hard roof activation above thegob UEILOGGER 300 data acquisition system made byAmerican UEL Company was used to monitor the evo-lution of the abutment stress 4e system consists of fourparts including the miniature pressure cell UEILOGGERhost data transmission cable and data processing software4e miniature pressure cell is capable of operating in thesaturated aqueous medium 4e measurement range of theminiature pressure cell is 002ndash15MPa the deviation islimited to 05 FS and acquisition frequency is set at 1 Hzin this monitoring programme 4e acoustic emissionmonitoring system (AEwin) made by American PhysicalAcoustics Corporation was used to monitor acousticemission signals 4is system also consists of four partsincluding the acoustic emission sensor the acoustic

emission host the data transmission cable and data pro-cessing software 4e measurement range is 1 kHzndash3MHzvibration frequency and maximum acquisition frequencyreaches 40MHz for the acoustic emission monitoringsystem 4e resonant frequency the sensitivity peak andthe effective acquisition frequency of the acoustic emissionsensor are 40 kHz 75 dB and 15 kHzndash70 kHz in thismonitoring programme respectively In addition TS3866digital photogrammetry system was used to monitor therock strata displacement

Figure 4 shows the layout of monitoring points forthree monitoring systems Six miniature pressure cells (P1to P6 in Figure 4) eight acoustic emission sensors (S1 to S8in Figure 4) and 144 monitoring points of displacement(Measuring line 1 to Measuring line 6 in Figure 4) arearranged in this physical model 4ree miniature pressurecells are used to record the abutment stress evolution in thecoal floor and three other miniature pressure cells are usedto record the abutment stress evolution around theretained entry Two of the acoustic emission sensors areused to record acoustic emission signals in the roof of theretained entry All the six measuring lines are used tomonitor the rock movement of different rock strata in theroof 4e detailed parameters of the monitoring pointsrsquolayout are presented in Figure 4

25 Physical Test Procedures 4e whole test involves sixsteps (1) Preparation of experimental tools such as the highstiff loading frame physical materials mixing barrel withelectric power electronic scale three monitoring systemsand other essential tools (2) Model and compact the eightphysical rock strata one by one and separate every rockstrata with certain mica powder (3) Apply the vertical load0056MPa through 20 loading rams in the top frame tosimulate the overburden loads fix the normal displacementin the floor boundary two-side boundaries with the frameand keep the free state for the front and back boundary of themodel after two months of the model completion (4)Conduct the excavation of the retained entry From the viewof mechanics the additional stress around the retained entrygenerally comes from the activation of the hard roofstructure near the retained entry while the collapsed hardroof structure in the gob center is independent of the ad-ditional stress around the retained entry (5) Perform thelongwall successively which retreats from the panel center topanel boundary to simulate the activation effect for the hardroof of the retained entry In each stage 50mm-long coal isexcavated by using a mini shovel 4en wait 20 minutesbefore the next excavation During the excavation threemonitoring systems should be operated in a normal state forrecording until the test procedure ends (6) Apply additionalvertical loading 200 Pa per second through the 20 loadingrams so as to simulate the abutment stress induced from theretreating of Panel 2 According to the existing monitoringdata in the field the additional vertical stress in the rock inthe front of the working face increased by 1729MPa in 24hours So the increasing rate can be calculated approximatelyas the 200 Pa per second

4 Advances in Civil Engineering

3 Results

31 Activation Characteristics of the Roof above the GobAs the pictures shown in Figure 5 the suspended roofencounters bending fracture and caving activation whenthe suspended area is large enough During the roof acti-vation the cantilever construction supports overburdenloads behind the coal body until it occurs fracture or cavingdown As shown in Figure 5(h) the cantilever constructionencounters fracture above the stiff coal pillar when applyingthe additional vertical stress in the top physical model Asshown in Figures 5(i)ndash5(k) the upper hard roof for instancethe fine sandstone which is strong enough to bear theoverburden loads is called the key stratum [36] is not cavingduring the longwall retreating in Panel 1 However as shownin Figure 5(l) it encounters fracture and caving activationwhen applying the additional vertical stress in the topphysical model

Along the vertical direction roof bends down in thelower roof near the gob initially and then the upper roof

begins to bend down gradually 4e lower roof is larger thanthe upper roof in vertical displacement distinctly As theincreasing distance from the gob center the roof verticaldisplacement decreases gradually as the measuring datashown in Figure 6(a) When the suspended area is largeenough the roof encounters fracture activation in-stantaneously and then cave activation in a short time asshown in Figure 6(b) However the soft stratum such as themudstone group encounters fracture and cave as long as thelower hard roof like the limestone fractures and caves As theincrease of the suspended area the roof encounters thefracture and caving activation and the increasing cavingzone compacts the gob gradually as shown from Figure 6(b)to Figure 6(e)

32 Evolution of the Additional Abutment Stress At firstadditional abutment stress increases slowly then decreasessharply and presents stabilization finally in P1 P2 and P3 asshown in Figures 7(a)ndash7(c)4e stable value is less than zero

Table 1 Materials used in the physical model

Lithology UCS of prototype(MPa)

UCS of model(kPa) Sand (kg) Calcium carbonate (kg) Gypsum (kg) Amounts (kg) Water (L)

Mudstone group 1 3527 14406 7031 703 703 8438 938Medium sandstone 7009 28630 15820 1582 3691 21094 2344Mudstone group 2 3527 14406 58594 5859 5859 70313 7813Fine sandstone 7461 30481 18984 1898 4430 25313 3616Mudstone group 3 3527 14406 38672 3867 3867 46406 5156Limestone 7183 29342 14238 1424 3322 18984 2712Coal seam 15 2483 10141 7998 571 571 9141 1016Mudstone 2971 12135 12054 1004 1004 14063 1563

P1 P2 P3

P5 P4

P6

Miniature pressure cell

Mudstone group

Mudstone group

Unit cm

Fine sandstone

Limestone

Acoustic emission sensor

S1 and S5

S2 and S6 S3 and S7

S4 and S8

375045

00

3000 3000 3000

5000

110

00

3500

1875

3000

343835

00

25000

Measuringline 1

Measuringline 2

Measuringline 3

Measuringline 4

Measuringline 5

Measuringline 6

Medium sandstone

Monitoring point of displacement

Figure 4 Monitoring programme in the physical model

Advances in Civil Engineering 5

Besides applying additional vertical stress in the top modelis independent of the additional abutment stress in P1 P2and P3 Peaks of the additional abutment stress in P2 and P3are larger than that in P1 and the inflection point occurswhen the coal is mined out above the measuring point Inaddition at first the additional abutment stress increasesslowly then increases sharply decreases sharply afterwardsand presents stabilization in the final in P4 P5 and P6 asshown in Figures 7(d)ndash7(f) Additional abutment stress in P5is larger than that in P4 and P6 in amplification and whoseminimum is in P4 However applying additional verticalstress in the top of the model can increase the abutmentstress in P4 P5 and P6 greatly

33 Characteristics of the Acoustic Emission SignalsDistinct acoustic emission phenomenon occurs during thehard roof activation above the gob as measuring point S4 inFigure 8 4e ring count indicates that the number of the

effective acoustic emission signals exceeds the thresholdvalue Obviously the ring count turns to the saltation stateinstantaneously during the layered caving and cantileverconstruction fracture but it always equals to zero when theroof is relatively stable as shown in Figure 8(a) 4e peak ofthe ring count occurs when applying the additional verticalstress in the top of the model 4e energy the area of thedetection signal envelope reflects the strength of theacoustic emission signal As shown in Figure 8(b) the ringcount turns to the saltation state instantaneously whenlayered caving and cantilever construction fracture occurbut it always equals to zero when the roof is relatively stableWhen additional vertical stress is applied the energymonitored is much greater than that in other time In ad-dition the amplitude the range of the acoustic emissionwave envelope is messy but is relatively large during thehard roof activation above the gob as shown in Figure 8(c)Similarly it reaches the peak when applying the additionalvertical stress in the top of the model

(a) (b) (c)

(d) (e) (f )

(g) (h) (i)

(j) (k) (l)

Figure 5 Roof activation characteristics (a) Roof bending (b) Roof fracture (c) Roof caving (d) Cantilever construction (e) Cantileverconstruction fracture (f ) Cantilever construction caving (g) Cantilever construction (h) Cantilever construction fracture (i) Upper roofcondition (j) Suspended upper roof (k) Upper roof fracture (l) Upper roof fracture and caving

6 Advances in Civil Engineering

0 200 400 600 800 1000ndash12

ndash09

ndash06

ndash03

00

Boundary

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundaryEntry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(a)

0 200 400 600 800 1000ndash25

ndash20

ndash15

ndash10

ndash05

00

Caving

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundary

Boundary

Entry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(b)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Outlier Fracture

Gob boundary

Caving

Entry

Caving down

Bend down

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Boundary

(c)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving

Boundary

Caving down

Outlier

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

Entry

(d)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Fracture

Caving

Caving down

Entry

Boundary

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

(e)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving down

EntryCaving

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

BoundaryBend down

(f )

Figure 6 Vertical displacement of the roofs above the gob (a) Panel 1 retreating 500mm (b) Panel 1 retreating 650mm (c) Panel 1retreating 1150mm (d) Panel 1 retreating 1200mm (e) Panel 1 retreating 1600mm (f) Applying additional abutment stress

Advances in Civil Engineering 7

4 Discussion

In mining excavation stiff coal-pillar entry retaining isunder the condition of strong mine ground pressure which

is validated by the physical method 4e rock around theretained entry experiences not only the evolution of the sideabutment stress and the front abutment stress [37] but alsothe loading of dynamic stress induced from the fracture and

0 5 10 15 20 25 30ndash4

ndash3

ndash2

ndash1

0

1

Appling additionalvertical stress

Increasing

DecreasingStabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P1

50

P1 is in the gob floor

(a)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P2

50

P2 is in the gob floor

(b)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P3

50

P3 is in the gob

(c)

0 5 10 15 20 25 300

5

10

15

20

25

Increasing sharply

Stabilization

Peak

Increasing slowly

Applying additional vertical stress

P4 is in the solid coal

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P4

50

(d)

0 5 10 15 20 25 300

10

20

30

40

50

60

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P5 is in the stiff coal pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P5

50

(e)

0 5 10 15 20 25 300

10

20

30

40

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P6 is in the hard roof above the pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P6

50

(f )

Figure 7 Additional abutment stress evolution during the hard roof activation above the gob (a) Measuring point of P1 (b) Measuringpoint of P2 (c) Measuring point of P3 (d) Measuring point of P4 (e) Measuring point of P5 (f ) Measuring point of P6

8 Advances in Civil Engineering

caving activation for the hard roof When the strength andthe stiffness are insufficient to support the overburden loadsthe hard roof structure experiences fracture and cavingactivation like the limestone shown in Figure 5 4e cu-mulative energy of elastic deformation in the structuremay release the dynamic stress instantaneously [38] Whenthe dynamic stress waves to the underground space likethe retained entry dynamic disasters such as the large

deformation in short time occur even if the retained entry isprotected with a stiff coal pillar such as deformation resultsof the retained entry shown in Figure 9

4e suspended roof encounters bending fracture andcaving activation when the suspended area is largeenough During the activation process overlying loadsabove the worked-out area have a loading effect on theunworked-out area Besides the generating dynamic

0 5 10 15 20 25 30 35

0

1000

2000

3000

4000

Retreating distance of panel 1 (cm)Ri

ng co

unt (

time)

Time (times1000s)S4

0 25 50 65 115 160

Layered caving

Cantilever construction fracture

Applying additional vertical stress

(a)

S4

ndash5 0 5 10 15 20 25 30 35ndash10000

0

10000

20000

30000

40000

50000

60000

70000

ndash5 0 5 10 15 20 250

400

800

1200

1600

2000

Constructionfracture

Layered caving

Retreating distance of panel 1 (cm)

Ener

gy (u

vmiddotm

s)

Time (times1000s)

Applying additional vertical stress

0 25 50 65 115 160

0 25 50 65 115

(b)

ndash5 0 5 10 15 20 25 30 3520

40

60

80

100

Retreating distance of panel 1 (cm)

Am

plitu

de (d

B)

Time (times1000s)

0 25 50 65 115 160

Average 3798dB

S4

(c)

Figure 8 Acoustic emission signals during the activation of the hard roof above the gob (a) Ring count in measuring point S4 (b) Energiesin measuring point S4 (c) Amplitude in measuring point S4

Figure 9 Deformation characteristics of the 195m stiff coal-pillar entry retaining [39] 4e entry experiences the whole hard roofactivation above the gob

Advances in Civil Engineering 9

stress wave to the nearby retained entry which makes therock around the retained entry under the synergy effect ofabutment stress and dynamic stress 4e results of miningground pressure in the physical model of plane stress canclearly illustrate the mechanical behavior of the rockaround the retained entry with stiff coal pillar under thehard roof [40]

However the physical model can only simulate themechanical behavior of the rock strata behind the workingface during the mining process when it is under the plane-stress condition When there are several hard roofs nearthe mining coal seam this experimental method is a greatoption for predicting the mine ground pressure of the stiffcoal-pillar entry retaining while it is inappropriate forpredicting the deformation behavior of the retained entrywhen the dimension of the entry is just 31mm in widthand 25mm in height In addition when monitoring thedynamic stress induced from the hard roof activationthe monitoring system of high-frequency pressure cell ismore convinced than vibration signals with the acousticemission

5 Conclusions

In order to reveal the mine ground pressure of stiff coal-pillar entry retaining and verify whether this entry can beretained to serve the next panel influenced by the hard roofactivation a 2D physical model with plane-stress conditionswas established to simulate the mechanical behavior of hardroofs behind the working face 4e results of the experi-mental method are concluded as follows

(1) 4e hard roof closed to the gob undergoes bendingdown fracture and caving activation successivelyunless its upper hard roof is strong enough tosupport overlying loads 4e cantilever structurewhich is supported by the stiff coal pillar above thegob faces the potential fracture activation above thestiff coal pillar under the front abutment stress in-duced from the retreating of the next panel

(2) Under the synergistic effects of the side varyingabutment stress and dynamic stress the entrycannot be retained to serve next panel successfullyeven though it is protected with a stiff coal pillarOverlying loads above the worked-out area mainlyhave a loading effect in the stiff coal pillar Besidesthe dynamic stress induced from the hard roofactivation can wave to the underneath retainedentry

(3) 4e experimental method can be used to analyze themechanical behavior of the rock strata during themining process Since the geological and engineeringconditions are different the procedure is still nec-essary for other cases

Data Availability

4e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

4e authors declare that they have no conflicts of interest

Acknowledgments

4is work was supported by the National Natural ScienceFoundation of China (contract nos 51804099 51774111 and51704098) the Key Scientific Research Project Fund ofColleges and Universities of Henan Province (19A440011and 19A130001) the Natural Science Foundation of HenanPolytechnic University (B2018-4 and B2018-65) and theRegional Collaborative Innovation Project of the XinjiangUygur Autonomous Region (2017E0292)

References

[1] P K Mandal R Singh J Maiti A K Singh R Kumar andA Sinha ldquoUnderpinning-based simultaneous extraction ofcontiguous sections of a thick coal seam under weak andlaminated partingrdquo International Journal of Rock Mechanicsand Mining Sciences vol 45 no 1 pp 11ndash28 2008

[2] M Colwell D Hill and R Frith ldquoALTS II a longwallgateroad design methodology for Australian collieriesrdquo inProceedings of the First Australasian Ground Control inMining Conference Sydney NSW Australia August 2003

[3] M Shabanimashcool and C C Li ldquoNumerical modelling oflongwall mining and stability analysis of the gates in a coalminerdquo International Journal of Rock Mechanics and MiningSciences vol 51 pp 24ndash34 2012

[4] Y Chen S Q Ma and Y Yu ldquoStability control of un-derground roadways subjected to stresses caused by extrac-tion of a 10-m-thick coal seam a case studyrdquo Rock Mechanicsand Rock Engineering vol 50 no 9 pp 1ndash10 2017

[5] M Colwell R Frith and C Mark ldquoAnalysis of longwalltailgate serviceability (ALTS) a chain pillar design method-ology for Australian conditionsrdquo in Proceedings of the SecondInternational Workshop on Coal Pillar Mechanics and Designpp 33ndash48 1999

[6] J B Bai and C J Hou ldquoNumerical simulation study onstability of narrow coal pillar of roadway driving along goafrdquoChinese Journal of Rock Mechanics and Engineering vol 23no 20 pp 3475ndash3479 2004

[7] E Jirankova V Petros and J Sancer ldquo4e assessment ofstress in an exploited rock mass based on the disturbance ofthe rigid overlying stratardquo International Journal of RockMechanics and Mining Sciences vol 50 pp 77ndash82 2012

[8] G Zhang Y Tan S Liang and H Jia ldquoNumerical estimationof suitable gob-side filling wall width in a highly gassylongwall mining panelrdquo International Journal of Geo-mechanics vol 18 no 8 article 04018091 2018

[9] G Zhang S Liang Y Tan F X Xie S Chen and H JialdquoNumerical modeling for longwall pillar design a case studyfrom a typical longwall panel in Chinardquo Journal of Geophysicsand Engineering vol 15 no 1 pp 121ndash134 2018

[10] E Esterhuizen C Mark and M M Murphy ldquoNumericalmodel calibration for simulating coal pillars gob and over-burden responserdquo in Proceedings of the Twenty-Ninth In-ternational Conference on Ground Control in Miningpp 46ndash57 Morgantown WV USA July 2010

[11] W F Li J B Bai S Peng X Y Wang and Y Xu ldquoNumericalmodeling for yield pillar design a case studyrdquo RockMechanicsand Rock Engineering vol 48 no 1 pp 305ndash318 2014

10 Advances in Civil Engineering

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

Advances in Civil Engineering 11

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control system a high stiff loading frame and three mon-itoring systems 4e dimension of the physical model rea-ches 25m in length 03m in width and 2m in heightUnder the geological and engineering condition of theretained entry in Panel 2 of First Yangquan coal mine therock strata of 400m long in the field were established tosimulate the mechanical behavior in Panel 1 of 220m long

the stiff coal pillar of 15m long the retained entry of 5mlong partial Panel 2 of 80m long and the boundary of 80mlong in the physical model According to the similaritytheory [34] strength density and geometry should followthe particular relationship as Equation (1) For this worksimilarity ratios of CLCρCσ Ct are determined as 160 1532448 and 1265 respectively

Lithology

Medium sandstoneSiltstoneSandy mudstoneSilty mudstoneMudstone

LimestoneCoal seam 15

Sandy mudstone

Sandy mudstone

Sandy mudstoneMudstone

Mudstone

Mudstone

Siltstone

Fine sandstone

ickness(m)

Depth(m)

Remarks

23050

10050

200180100208020

1101356520

100

479048404940

50905290547055705590567056905800593560006020

4990

Coal seamHard roof

Mudstone group

Hard roof

Hard roof100 4690

Mudstone group

Mudstone

MudstoneMudstone

Figure 2 Generalized stratigraphic column

Monitoringpoint of

displacement

Miniaturepressure

cell

Acousticemission

sensor

Loading ram

Physical model Experimental sceneServo load

control system

TS3866photogrammetric system

Acoustic emissionmonitoring system

UEILOGGERdata acquisition system

Loading frame

Figure 3 Experimental scene with physical model and monitoring systems

Advances in Civil Engineering 3

Cσ

CρCL

1

CL Lp

Lm

Cσ σpσm

Cρ ρpρm

Ct CLCL

1113968

⎧⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎩

(1)

where CL Cσ and Ct are the similarity ratios of geometrystrength and time respectively Cρ is the density simi-larity ratio between the prototype and the model Lp σpand ρp represent the dimension strength and density ofthe rock strata in the field Lm σm and ρm represent thedimension strength and density of the rock strata in themodel

23 Physical Materials As shown in Figure 2 eight ma-terials with different deformability and strength are usedto simulate the mechanical behavior of the rock strataincluding mudstone coal seam 15 limestone mudstonegroup 1 fine sandstone mudstone group 2 mediumsandstone and mudstone group 3 Physical materials aremingled with sand gypsum calcium carbonate waterand mica powder Under the condition of the uniaxialcompression test and the strength similarity ratio theratio of the material contents is determined based on theexisting results [35] For this work eight materials arepresented in Table 1 Totally 173391 kg sand 16910 kgcalcium carbonate 23449 kg gypsum and 25 kg micapowder are deserved in this model

24 Monitoring Instruments and Methods Evolution of theabutment stress acoustic emission signals and the rockstrata displacement are determined as indexes of the mineground pressure during the hard roof activation above thegob UEILOGGER 300 data acquisition system made byAmerican UEL Company was used to monitor the evo-lution of the abutment stress 4e system consists of fourparts including the miniature pressure cell UEILOGGERhost data transmission cable and data processing software4e miniature pressure cell is capable of operating in thesaturated aqueous medium 4e measurement range of theminiature pressure cell is 002ndash15MPa the deviation islimited to 05 FS and acquisition frequency is set at 1 Hzin this monitoring programme 4e acoustic emissionmonitoring system (AEwin) made by American PhysicalAcoustics Corporation was used to monitor acousticemission signals 4is system also consists of four partsincluding the acoustic emission sensor the acoustic

emission host the data transmission cable and data pro-cessing software 4e measurement range is 1 kHzndash3MHzvibration frequency and maximum acquisition frequencyreaches 40MHz for the acoustic emission monitoringsystem 4e resonant frequency the sensitivity peak andthe effective acquisition frequency of the acoustic emissionsensor are 40 kHz 75 dB and 15 kHzndash70 kHz in thismonitoring programme respectively In addition TS3866digital photogrammetry system was used to monitor therock strata displacement

Figure 4 shows the layout of monitoring points forthree monitoring systems Six miniature pressure cells (P1to P6 in Figure 4) eight acoustic emission sensors (S1 to S8in Figure 4) and 144 monitoring points of displacement(Measuring line 1 to Measuring line 6 in Figure 4) arearranged in this physical model 4ree miniature pressurecells are used to record the abutment stress evolution in thecoal floor and three other miniature pressure cells are usedto record the abutment stress evolution around theretained entry Two of the acoustic emission sensors areused to record acoustic emission signals in the roof of theretained entry All the six measuring lines are used tomonitor the rock movement of different rock strata in theroof 4e detailed parameters of the monitoring pointsrsquolayout are presented in Figure 4

25 Physical Test Procedures 4e whole test involves sixsteps (1) Preparation of experimental tools such as the highstiff loading frame physical materials mixing barrel withelectric power electronic scale three monitoring systemsand other essential tools (2) Model and compact the eightphysical rock strata one by one and separate every rockstrata with certain mica powder (3) Apply the vertical load0056MPa through 20 loading rams in the top frame tosimulate the overburden loads fix the normal displacementin the floor boundary two-side boundaries with the frameand keep the free state for the front and back boundary of themodel after two months of the model completion (4)Conduct the excavation of the retained entry From the viewof mechanics the additional stress around the retained entrygenerally comes from the activation of the hard roofstructure near the retained entry while the collapsed hardroof structure in the gob center is independent of the ad-ditional stress around the retained entry (5) Perform thelongwall successively which retreats from the panel center topanel boundary to simulate the activation effect for the hardroof of the retained entry In each stage 50mm-long coal isexcavated by using a mini shovel 4en wait 20 minutesbefore the next excavation During the excavation threemonitoring systems should be operated in a normal state forrecording until the test procedure ends (6) Apply additionalvertical loading 200 Pa per second through the 20 loadingrams so as to simulate the abutment stress induced from theretreating of Panel 2 According to the existing monitoringdata in the field the additional vertical stress in the rock inthe front of the working face increased by 1729MPa in 24hours So the increasing rate can be calculated approximatelyas the 200 Pa per second

4 Advances in Civil Engineering

3 Results

31 Activation Characteristics of the Roof above the GobAs the pictures shown in Figure 5 the suspended roofencounters bending fracture and caving activation whenthe suspended area is large enough During the roof acti-vation the cantilever construction supports overburdenloads behind the coal body until it occurs fracture or cavingdown As shown in Figure 5(h) the cantilever constructionencounters fracture above the stiff coal pillar when applyingthe additional vertical stress in the top physical model Asshown in Figures 5(i)ndash5(k) the upper hard roof for instancethe fine sandstone which is strong enough to bear theoverburden loads is called the key stratum [36] is not cavingduring the longwall retreating in Panel 1 However as shownin Figure 5(l) it encounters fracture and caving activationwhen applying the additional vertical stress in the topphysical model

Along the vertical direction roof bends down in thelower roof near the gob initially and then the upper roof

begins to bend down gradually 4e lower roof is larger thanthe upper roof in vertical displacement distinctly As theincreasing distance from the gob center the roof verticaldisplacement decreases gradually as the measuring datashown in Figure 6(a) When the suspended area is largeenough the roof encounters fracture activation in-stantaneously and then cave activation in a short time asshown in Figure 6(b) However the soft stratum such as themudstone group encounters fracture and cave as long as thelower hard roof like the limestone fractures and caves As theincrease of the suspended area the roof encounters thefracture and caving activation and the increasing cavingzone compacts the gob gradually as shown from Figure 6(b)to Figure 6(e)

32 Evolution of the Additional Abutment Stress At firstadditional abutment stress increases slowly then decreasessharply and presents stabilization finally in P1 P2 and P3 asshown in Figures 7(a)ndash7(c)4e stable value is less than zero

Table 1 Materials used in the physical model

Lithology UCS of prototype(MPa)

UCS of model(kPa) Sand (kg) Calcium carbonate (kg) Gypsum (kg) Amounts (kg) Water (L)

Mudstone group 1 3527 14406 7031 703 703 8438 938Medium sandstone 7009 28630 15820 1582 3691 21094 2344Mudstone group 2 3527 14406 58594 5859 5859 70313 7813Fine sandstone 7461 30481 18984 1898 4430 25313 3616Mudstone group 3 3527 14406 38672 3867 3867 46406 5156Limestone 7183 29342 14238 1424 3322 18984 2712Coal seam 15 2483 10141 7998 571 571 9141 1016Mudstone 2971 12135 12054 1004 1004 14063 1563

P1 P2 P3

P5 P4

P6

Miniature pressure cell

Mudstone group

Mudstone group

Unit cm

Fine sandstone

Limestone

Acoustic emission sensor

S1 and S5

S2 and S6 S3 and S7

S4 and S8

375045

00

3000 3000 3000

5000

110

00

3500

1875

3000

343835

00

25000

Measuringline 1

Measuringline 2

Measuringline 3

Measuringline 4

Measuringline 5

Measuringline 6

Medium sandstone

Monitoring point of displacement

Figure 4 Monitoring programme in the physical model

Advances in Civil Engineering 5

Besides applying additional vertical stress in the top modelis independent of the additional abutment stress in P1 P2and P3 Peaks of the additional abutment stress in P2 and P3are larger than that in P1 and the inflection point occurswhen the coal is mined out above the measuring point Inaddition at first the additional abutment stress increasesslowly then increases sharply decreases sharply afterwardsand presents stabilization in the final in P4 P5 and P6 asshown in Figures 7(d)ndash7(f) Additional abutment stress in P5is larger than that in P4 and P6 in amplification and whoseminimum is in P4 However applying additional verticalstress in the top of the model can increase the abutmentstress in P4 P5 and P6 greatly

33 Characteristics of the Acoustic Emission SignalsDistinct acoustic emission phenomenon occurs during thehard roof activation above the gob as measuring point S4 inFigure 8 4e ring count indicates that the number of the

effective acoustic emission signals exceeds the thresholdvalue Obviously the ring count turns to the saltation stateinstantaneously during the layered caving and cantileverconstruction fracture but it always equals to zero when theroof is relatively stable as shown in Figure 8(a) 4e peak ofthe ring count occurs when applying the additional verticalstress in the top of the model 4e energy the area of thedetection signal envelope reflects the strength of theacoustic emission signal As shown in Figure 8(b) the ringcount turns to the saltation state instantaneously whenlayered caving and cantilever construction fracture occurbut it always equals to zero when the roof is relatively stableWhen additional vertical stress is applied the energymonitored is much greater than that in other time In ad-dition the amplitude the range of the acoustic emissionwave envelope is messy but is relatively large during thehard roof activation above the gob as shown in Figure 8(c)Similarly it reaches the peak when applying the additionalvertical stress in the top of the model

(a) (b) (c)

(d) (e) (f )

(g) (h) (i)

(j) (k) (l)

Figure 5 Roof activation characteristics (a) Roof bending (b) Roof fracture (c) Roof caving (d) Cantilever construction (e) Cantileverconstruction fracture (f ) Cantilever construction caving (g) Cantilever construction (h) Cantilever construction fracture (i) Upper roofcondition (j) Suspended upper roof (k) Upper roof fracture (l) Upper roof fracture and caving

6 Advances in Civil Engineering

0 200 400 600 800 1000ndash12

ndash09

ndash06

ndash03

00

Boundary

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundaryEntry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(a)

0 200 400 600 800 1000ndash25

ndash20

ndash15

ndash10

ndash05

00

Caving

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundary

Boundary

Entry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(b)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Outlier Fracture

Gob boundary

Caving

Entry

Caving down

Bend down

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Boundary

(c)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving

Boundary

Caving down

Outlier

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

Entry

(d)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Fracture

Caving

Caving down

Entry

Boundary

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

(e)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving down

EntryCaving

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

BoundaryBend down

(f )

Figure 6 Vertical displacement of the roofs above the gob (a) Panel 1 retreating 500mm (b) Panel 1 retreating 650mm (c) Panel 1retreating 1150mm (d) Panel 1 retreating 1200mm (e) Panel 1 retreating 1600mm (f) Applying additional abutment stress

Advances in Civil Engineering 7

4 Discussion

In mining excavation stiff coal-pillar entry retaining isunder the condition of strong mine ground pressure which

is validated by the physical method 4e rock around theretained entry experiences not only the evolution of the sideabutment stress and the front abutment stress [37] but alsothe loading of dynamic stress induced from the fracture and

0 5 10 15 20 25 30ndash4

ndash3

ndash2

ndash1

0

1

Appling additionalvertical stress

Increasing

DecreasingStabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P1

50

P1 is in the gob floor

(a)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P2

50

P2 is in the gob floor

(b)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P3

50

P3 is in the gob

(c)

0 5 10 15 20 25 300

5

10

15

20

25

Increasing sharply

Stabilization

Peak

Increasing slowly

Applying additional vertical stress

P4 is in the solid coal

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P4

50

(d)

0 5 10 15 20 25 300

10

20

30

40

50

60

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P5 is in the stiff coal pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P5

50

(e)

0 5 10 15 20 25 300

10

20

30

40

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P6 is in the hard roof above the pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P6

50

(f )

Figure 7 Additional abutment stress evolution during the hard roof activation above the gob (a) Measuring point of P1 (b) Measuringpoint of P2 (c) Measuring point of P3 (d) Measuring point of P4 (e) Measuring point of P5 (f ) Measuring point of P6

8 Advances in Civil Engineering

caving activation for the hard roof When the strength andthe stiffness are insufficient to support the overburden loadsthe hard roof structure experiences fracture and cavingactivation like the limestone shown in Figure 5 4e cu-mulative energy of elastic deformation in the structuremay release the dynamic stress instantaneously [38] Whenthe dynamic stress waves to the underground space likethe retained entry dynamic disasters such as the large

deformation in short time occur even if the retained entry isprotected with a stiff coal pillar such as deformation resultsof the retained entry shown in Figure 9

4e suspended roof encounters bending fracture andcaving activation when the suspended area is largeenough During the activation process overlying loadsabove the worked-out area have a loading effect on theunworked-out area Besides the generating dynamic

0 5 10 15 20 25 30 35

0

1000

2000

3000

4000

Retreating distance of panel 1 (cm)Ri

ng co

unt (

time)

Time (times1000s)S4

0 25 50 65 115 160

Layered caving

Cantilever construction fracture

Applying additional vertical stress

(a)

S4

ndash5 0 5 10 15 20 25 30 35ndash10000

0

10000

20000

30000

40000

50000

60000

70000

ndash5 0 5 10 15 20 250

400

800

1200

1600

2000

Constructionfracture

Layered caving

Retreating distance of panel 1 (cm)

Ener

gy (u

vmiddotm

s)

Time (times1000s)

Applying additional vertical stress

0 25 50 65 115 160

0 25 50 65 115

(b)

ndash5 0 5 10 15 20 25 30 3520

40

60

80

100

Retreating distance of panel 1 (cm)

Am

plitu

de (d

B)

Time (times1000s)

0 25 50 65 115 160

Average 3798dB

S4

(c)

Figure 8 Acoustic emission signals during the activation of the hard roof above the gob (a) Ring count in measuring point S4 (b) Energiesin measuring point S4 (c) Amplitude in measuring point S4

Figure 9 Deformation characteristics of the 195m stiff coal-pillar entry retaining [39] 4e entry experiences the whole hard roofactivation above the gob

Advances in Civil Engineering 9

stress wave to the nearby retained entry which makes therock around the retained entry under the synergy effect ofabutment stress and dynamic stress 4e results of miningground pressure in the physical model of plane stress canclearly illustrate the mechanical behavior of the rockaround the retained entry with stiff coal pillar under thehard roof [40]

However the physical model can only simulate themechanical behavior of the rock strata behind the workingface during the mining process when it is under the plane-stress condition When there are several hard roofs nearthe mining coal seam this experimental method is a greatoption for predicting the mine ground pressure of the stiffcoal-pillar entry retaining while it is inappropriate forpredicting the deformation behavior of the retained entrywhen the dimension of the entry is just 31mm in widthand 25mm in height In addition when monitoring thedynamic stress induced from the hard roof activationthe monitoring system of high-frequency pressure cell ismore convinced than vibration signals with the acousticemission

5 Conclusions

In order to reveal the mine ground pressure of stiff coal-pillar entry retaining and verify whether this entry can beretained to serve the next panel influenced by the hard roofactivation a 2D physical model with plane-stress conditionswas established to simulate the mechanical behavior of hardroofs behind the working face 4e results of the experi-mental method are concluded as follows

(1) 4e hard roof closed to the gob undergoes bendingdown fracture and caving activation successivelyunless its upper hard roof is strong enough tosupport overlying loads 4e cantilever structurewhich is supported by the stiff coal pillar above thegob faces the potential fracture activation above thestiff coal pillar under the front abutment stress in-duced from the retreating of the next panel

(2) Under the synergistic effects of the side varyingabutment stress and dynamic stress the entrycannot be retained to serve next panel successfullyeven though it is protected with a stiff coal pillarOverlying loads above the worked-out area mainlyhave a loading effect in the stiff coal pillar Besidesthe dynamic stress induced from the hard roofactivation can wave to the underneath retainedentry

(3) 4e experimental method can be used to analyze themechanical behavior of the rock strata during themining process Since the geological and engineeringconditions are different the procedure is still nec-essary for other cases

Data Availability

4e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

4e authors declare that they have no conflicts of interest

Acknowledgments

4is work was supported by the National Natural ScienceFoundation of China (contract nos 51804099 51774111 and51704098) the Key Scientific Research Project Fund ofColleges and Universities of Henan Province (19A440011and 19A130001) the Natural Science Foundation of HenanPolytechnic University (B2018-4 and B2018-65) and theRegional Collaborative Innovation Project of the XinjiangUygur Autonomous Region (2017E0292)

References

[1] P K Mandal R Singh J Maiti A K Singh R Kumar andA Sinha ldquoUnderpinning-based simultaneous extraction ofcontiguous sections of a thick coal seam under weak andlaminated partingrdquo International Journal of Rock Mechanicsand Mining Sciences vol 45 no 1 pp 11ndash28 2008

[2] M Colwell D Hill and R Frith ldquoALTS II a longwallgateroad design methodology for Australian collieriesrdquo inProceedings of the First Australasian Ground Control inMining Conference Sydney NSW Australia August 2003

[3] M Shabanimashcool and C C Li ldquoNumerical modelling oflongwall mining and stability analysis of the gates in a coalminerdquo International Journal of Rock Mechanics and MiningSciences vol 51 pp 24ndash34 2012

[4] Y Chen S Q Ma and Y Yu ldquoStability control of un-derground roadways subjected to stresses caused by extrac-tion of a 10-m-thick coal seam a case studyrdquo Rock Mechanicsand Rock Engineering vol 50 no 9 pp 1ndash10 2017

[5] M Colwell R Frith and C Mark ldquoAnalysis of longwalltailgate serviceability (ALTS) a chain pillar design method-ology for Australian conditionsrdquo in Proceedings of the SecondInternational Workshop on Coal Pillar Mechanics and Designpp 33ndash48 1999

[6] J B Bai and C J Hou ldquoNumerical simulation study onstability of narrow coal pillar of roadway driving along goafrdquoChinese Journal of Rock Mechanics and Engineering vol 23no 20 pp 3475ndash3479 2004

[7] E Jirankova V Petros and J Sancer ldquo4e assessment ofstress in an exploited rock mass based on the disturbance ofthe rigid overlying stratardquo International Journal of RockMechanics and Mining Sciences vol 50 pp 77ndash82 2012

[8] G Zhang Y Tan S Liang and H Jia ldquoNumerical estimationof suitable gob-side filling wall width in a highly gassylongwall mining panelrdquo International Journal of Geo-mechanics vol 18 no 8 article 04018091 2018

[9] G Zhang S Liang Y Tan F X Xie S Chen and H JialdquoNumerical modeling for longwall pillar design a case studyfrom a typical longwall panel in Chinardquo Journal of Geophysicsand Engineering vol 15 no 1 pp 121ndash134 2018

[10] E Esterhuizen C Mark and M M Murphy ldquoNumericalmodel calibration for simulating coal pillars gob and over-burden responserdquo in Proceedings of the Twenty-Ninth In-ternational Conference on Ground Control in Miningpp 46ndash57 Morgantown WV USA July 2010

[11] W F Li J B Bai S Peng X Y Wang and Y Xu ldquoNumericalmodeling for yield pillar design a case studyrdquo RockMechanicsand Rock Engineering vol 48 no 1 pp 305ndash318 2014

10 Advances in Civil Engineering

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

Advances in Civil Engineering 11

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Submit your manuscripts atwwwhindawicom

Cσ

CρCL

1

CL Lp

Lm

Cσ σpσm

Cρ ρpρm

Ct CLCL

1113968

⎧⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎩

(1)

where CL Cσ and Ct are the similarity ratios of geometrystrength and time respectively Cρ is the density simi-larity ratio between the prototype and the model Lp σpand ρp represent the dimension strength and density ofthe rock strata in the field Lm σm and ρm represent thedimension strength and density of the rock strata in themodel

23 Physical Materials As shown in Figure 2 eight ma-terials with different deformability and strength are usedto simulate the mechanical behavior of the rock strataincluding mudstone coal seam 15 limestone mudstonegroup 1 fine sandstone mudstone group 2 mediumsandstone and mudstone group 3 Physical materials aremingled with sand gypsum calcium carbonate waterand mica powder Under the condition of the uniaxialcompression test and the strength similarity ratio theratio of the material contents is determined based on theexisting results [35] For this work eight materials arepresented in Table 1 Totally 173391 kg sand 16910 kgcalcium carbonate 23449 kg gypsum and 25 kg micapowder are deserved in this model

24 Monitoring Instruments and Methods Evolution of theabutment stress acoustic emission signals and the rockstrata displacement are determined as indexes of the mineground pressure during the hard roof activation above thegob UEILOGGER 300 data acquisition system made byAmerican UEL Company was used to monitor the evo-lution of the abutment stress 4e system consists of fourparts including the miniature pressure cell UEILOGGERhost data transmission cable and data processing software4e miniature pressure cell is capable of operating in thesaturated aqueous medium 4e measurement range of theminiature pressure cell is 002ndash15MPa the deviation islimited to 05 FS and acquisition frequency is set at 1 Hzin this monitoring programme 4e acoustic emissionmonitoring system (AEwin) made by American PhysicalAcoustics Corporation was used to monitor acousticemission signals 4is system also consists of four partsincluding the acoustic emission sensor the acoustic

emission host the data transmission cable and data pro-cessing software 4e measurement range is 1 kHzndash3MHzvibration frequency and maximum acquisition frequencyreaches 40MHz for the acoustic emission monitoringsystem 4e resonant frequency the sensitivity peak andthe effective acquisition frequency of the acoustic emissionsensor are 40 kHz 75 dB and 15 kHzndash70 kHz in thismonitoring programme respectively In addition TS3866digital photogrammetry system was used to monitor therock strata displacement

Figure 4 shows the layout of monitoring points forthree monitoring systems Six miniature pressure cells (P1to P6 in Figure 4) eight acoustic emission sensors (S1 to S8in Figure 4) and 144 monitoring points of displacement(Measuring line 1 to Measuring line 6 in Figure 4) arearranged in this physical model 4ree miniature pressurecells are used to record the abutment stress evolution in thecoal floor and three other miniature pressure cells are usedto record the abutment stress evolution around theretained entry Two of the acoustic emission sensors areused to record acoustic emission signals in the roof of theretained entry All the six measuring lines are used tomonitor the rock movement of different rock strata in theroof 4e detailed parameters of the monitoring pointsrsquolayout are presented in Figure 4

25 Physical Test Procedures 4e whole test involves sixsteps (1) Preparation of experimental tools such as the highstiff loading frame physical materials mixing barrel withelectric power electronic scale three monitoring systemsand other essential tools (2) Model and compact the eightphysical rock strata one by one and separate every rockstrata with certain mica powder (3) Apply the vertical load0056MPa through 20 loading rams in the top frame tosimulate the overburden loads fix the normal displacementin the floor boundary two-side boundaries with the frameand keep the free state for the front and back boundary of themodel after two months of the model completion (4)Conduct the excavation of the retained entry From the viewof mechanics the additional stress around the retained entrygenerally comes from the activation of the hard roofstructure near the retained entry while the collapsed hardroof structure in the gob center is independent of the ad-ditional stress around the retained entry (5) Perform thelongwall successively which retreats from the panel center topanel boundary to simulate the activation effect for the hardroof of the retained entry In each stage 50mm-long coal isexcavated by using a mini shovel 4en wait 20 minutesbefore the next excavation During the excavation threemonitoring systems should be operated in a normal state forrecording until the test procedure ends (6) Apply additionalvertical loading 200 Pa per second through the 20 loadingrams so as to simulate the abutment stress induced from theretreating of Panel 2 According to the existing monitoringdata in the field the additional vertical stress in the rock inthe front of the working face increased by 1729MPa in 24hours So the increasing rate can be calculated approximatelyas the 200 Pa per second

4 Advances in Civil Engineering

3 Results

31 Activation Characteristics of the Roof above the GobAs the pictures shown in Figure 5 the suspended roofencounters bending fracture and caving activation whenthe suspended area is large enough During the roof acti-vation the cantilever construction supports overburdenloads behind the coal body until it occurs fracture or cavingdown As shown in Figure 5(h) the cantilever constructionencounters fracture above the stiff coal pillar when applyingthe additional vertical stress in the top physical model Asshown in Figures 5(i)ndash5(k) the upper hard roof for instancethe fine sandstone which is strong enough to bear theoverburden loads is called the key stratum [36] is not cavingduring the longwall retreating in Panel 1 However as shownin Figure 5(l) it encounters fracture and caving activationwhen applying the additional vertical stress in the topphysical model

Along the vertical direction roof bends down in thelower roof near the gob initially and then the upper roof

begins to bend down gradually 4e lower roof is larger thanthe upper roof in vertical displacement distinctly As theincreasing distance from the gob center the roof verticaldisplacement decreases gradually as the measuring datashown in Figure 6(a) When the suspended area is largeenough the roof encounters fracture activation in-stantaneously and then cave activation in a short time asshown in Figure 6(b) However the soft stratum such as themudstone group encounters fracture and cave as long as thelower hard roof like the limestone fractures and caves As theincrease of the suspended area the roof encounters thefracture and caving activation and the increasing cavingzone compacts the gob gradually as shown from Figure 6(b)to Figure 6(e)

32 Evolution of the Additional Abutment Stress At firstadditional abutment stress increases slowly then decreasessharply and presents stabilization finally in P1 P2 and P3 asshown in Figures 7(a)ndash7(c)4e stable value is less than zero

Table 1 Materials used in the physical model

Lithology UCS of prototype(MPa)

UCS of model(kPa) Sand (kg) Calcium carbonate (kg) Gypsum (kg) Amounts (kg) Water (L)

Mudstone group 1 3527 14406 7031 703 703 8438 938Medium sandstone 7009 28630 15820 1582 3691 21094 2344Mudstone group 2 3527 14406 58594 5859 5859 70313 7813Fine sandstone 7461 30481 18984 1898 4430 25313 3616Mudstone group 3 3527 14406 38672 3867 3867 46406 5156Limestone 7183 29342 14238 1424 3322 18984 2712Coal seam 15 2483 10141 7998 571 571 9141 1016Mudstone 2971 12135 12054 1004 1004 14063 1563

P1 P2 P3

P5 P4

P6

Miniature pressure cell

Mudstone group

Mudstone group

Unit cm

Fine sandstone

Limestone

Acoustic emission sensor

S1 and S5

S2 and S6 S3 and S7

S4 and S8

375045

00

3000 3000 3000

5000

110

00

3500

1875

3000

343835

00

25000

Measuringline 1

Measuringline 2

Measuringline 3

Measuringline 4

Measuringline 5

Measuringline 6

Medium sandstone

Monitoring point of displacement

Figure 4 Monitoring programme in the physical model

Advances in Civil Engineering 5

Besides applying additional vertical stress in the top modelis independent of the additional abutment stress in P1 P2and P3 Peaks of the additional abutment stress in P2 and P3are larger than that in P1 and the inflection point occurswhen the coal is mined out above the measuring point Inaddition at first the additional abutment stress increasesslowly then increases sharply decreases sharply afterwardsand presents stabilization in the final in P4 P5 and P6 asshown in Figures 7(d)ndash7(f) Additional abutment stress in P5is larger than that in P4 and P6 in amplification and whoseminimum is in P4 However applying additional verticalstress in the top of the model can increase the abutmentstress in P4 P5 and P6 greatly

33 Characteristics of the Acoustic Emission SignalsDistinct acoustic emission phenomenon occurs during thehard roof activation above the gob as measuring point S4 inFigure 8 4e ring count indicates that the number of the

effective acoustic emission signals exceeds the thresholdvalue Obviously the ring count turns to the saltation stateinstantaneously during the layered caving and cantileverconstruction fracture but it always equals to zero when theroof is relatively stable as shown in Figure 8(a) 4e peak ofthe ring count occurs when applying the additional verticalstress in the top of the model 4e energy the area of thedetection signal envelope reflects the strength of theacoustic emission signal As shown in Figure 8(b) the ringcount turns to the saltation state instantaneously whenlayered caving and cantilever construction fracture occurbut it always equals to zero when the roof is relatively stableWhen additional vertical stress is applied the energymonitored is much greater than that in other time In ad-dition the amplitude the range of the acoustic emissionwave envelope is messy but is relatively large during thehard roof activation above the gob as shown in Figure 8(c)Similarly it reaches the peak when applying the additionalvertical stress in the top of the model

(a) (b) (c)

(d) (e) (f )

(g) (h) (i)

(j) (k) (l)

Figure 5 Roof activation characteristics (a) Roof bending (b) Roof fracture (c) Roof caving (d) Cantilever construction (e) Cantileverconstruction fracture (f ) Cantilever construction caving (g) Cantilever construction (h) Cantilever construction fracture (i) Upper roofcondition (j) Suspended upper roof (k) Upper roof fracture (l) Upper roof fracture and caving

6 Advances in Civil Engineering

0 200 400 600 800 1000ndash12

ndash09

ndash06

ndash03

00

Boundary

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundaryEntry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(a)

0 200 400 600 800 1000ndash25

ndash20

ndash15

ndash10

ndash05

00

Caving

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundary

Boundary

Entry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(b)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Outlier Fracture

Gob boundary

Caving

Entry

Caving down

Bend down

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Boundary

(c)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving

Boundary

Caving down

Outlier

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

Entry

(d)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Fracture

Caving

Caving down

Entry

Boundary

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

(e)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving down

EntryCaving

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

BoundaryBend down

(f )

Figure 6 Vertical displacement of the roofs above the gob (a) Panel 1 retreating 500mm (b) Panel 1 retreating 650mm (c) Panel 1retreating 1150mm (d) Panel 1 retreating 1200mm (e) Panel 1 retreating 1600mm (f) Applying additional abutment stress

Advances in Civil Engineering 7

4 Discussion

In mining excavation stiff coal-pillar entry retaining isunder the condition of strong mine ground pressure which

is validated by the physical method 4e rock around theretained entry experiences not only the evolution of the sideabutment stress and the front abutment stress [37] but alsothe loading of dynamic stress induced from the fracture and

0 5 10 15 20 25 30ndash4

ndash3

ndash2

ndash1

0

1

Appling additionalvertical stress

Increasing

DecreasingStabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P1

50

P1 is in the gob floor

(a)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P2

50

P2 is in the gob floor

(b)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P3

50

P3 is in the gob

(c)

0 5 10 15 20 25 300

5

10

15

20

25

Increasing sharply

Stabilization

Peak

Increasing slowly

Applying additional vertical stress

P4 is in the solid coal

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P4

50

(d)

0 5 10 15 20 25 300

10

20

30

40

50

60

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P5 is in the stiff coal pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P5

50

(e)

0 5 10 15 20 25 300

10

20

30

40

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P6 is in the hard roof above the pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P6

50

(f )

Figure 7 Additional abutment stress evolution during the hard roof activation above the gob (a) Measuring point of P1 (b) Measuringpoint of P2 (c) Measuring point of P3 (d) Measuring point of P4 (e) Measuring point of P5 (f ) Measuring point of P6

8 Advances in Civil Engineering

caving activation for the hard roof When the strength andthe stiffness are insufficient to support the overburden loadsthe hard roof structure experiences fracture and cavingactivation like the limestone shown in Figure 5 4e cu-mulative energy of elastic deformation in the structuremay release the dynamic stress instantaneously [38] Whenthe dynamic stress waves to the underground space likethe retained entry dynamic disasters such as the large

deformation in short time occur even if the retained entry isprotected with a stiff coal pillar such as deformation resultsof the retained entry shown in Figure 9

4e suspended roof encounters bending fracture andcaving activation when the suspended area is largeenough During the activation process overlying loadsabove the worked-out area have a loading effect on theunworked-out area Besides the generating dynamic

0 5 10 15 20 25 30 35

0

1000

2000

3000

4000

Retreating distance of panel 1 (cm)Ri

ng co

unt (

time)

Time (times1000s)S4

0 25 50 65 115 160

Layered caving

Cantilever construction fracture

Applying additional vertical stress

(a)

S4

ndash5 0 5 10 15 20 25 30 35ndash10000

0

10000

20000

30000

40000

50000

60000

70000

ndash5 0 5 10 15 20 250

400

800

1200

1600

2000

Constructionfracture

Layered caving

Retreating distance of panel 1 (cm)

Ener

gy (u

vmiddotm

s)

Time (times1000s)

Applying additional vertical stress

0 25 50 65 115 160

0 25 50 65 115

(b)

ndash5 0 5 10 15 20 25 30 3520

40

60

80

100

Retreating distance of panel 1 (cm)

Am

plitu

de (d

B)

Time (times1000s)

0 25 50 65 115 160

Average 3798dB

S4

(c)

Figure 8 Acoustic emission signals during the activation of the hard roof above the gob (a) Ring count in measuring point S4 (b) Energiesin measuring point S4 (c) Amplitude in measuring point S4

Figure 9 Deformation characteristics of the 195m stiff coal-pillar entry retaining [39] 4e entry experiences the whole hard roofactivation above the gob

Advances in Civil Engineering 9

stress wave to the nearby retained entry which makes therock around the retained entry under the synergy effect ofabutment stress and dynamic stress 4e results of miningground pressure in the physical model of plane stress canclearly illustrate the mechanical behavior of the rockaround the retained entry with stiff coal pillar under thehard roof [40]

However the physical model can only simulate themechanical behavior of the rock strata behind the workingface during the mining process when it is under the plane-stress condition When there are several hard roofs nearthe mining coal seam this experimental method is a greatoption for predicting the mine ground pressure of the stiffcoal-pillar entry retaining while it is inappropriate forpredicting the deformation behavior of the retained entrywhen the dimension of the entry is just 31mm in widthand 25mm in height In addition when monitoring thedynamic stress induced from the hard roof activationthe monitoring system of high-frequency pressure cell ismore convinced than vibration signals with the acousticemission

5 Conclusions

In order to reveal the mine ground pressure of stiff coal-pillar entry retaining and verify whether this entry can beretained to serve the next panel influenced by the hard roofactivation a 2D physical model with plane-stress conditionswas established to simulate the mechanical behavior of hardroofs behind the working face 4e results of the experi-mental method are concluded as follows

(1) 4e hard roof closed to the gob undergoes bendingdown fracture and caving activation successivelyunless its upper hard roof is strong enough tosupport overlying loads 4e cantilever structurewhich is supported by the stiff coal pillar above thegob faces the potential fracture activation above thestiff coal pillar under the front abutment stress in-duced from the retreating of the next panel

(2) Under the synergistic effects of the side varyingabutment stress and dynamic stress the entrycannot be retained to serve next panel successfullyeven though it is protected with a stiff coal pillarOverlying loads above the worked-out area mainlyhave a loading effect in the stiff coal pillar Besidesthe dynamic stress induced from the hard roofactivation can wave to the underneath retainedentry

(3) 4e experimental method can be used to analyze themechanical behavior of the rock strata during themining process Since the geological and engineeringconditions are different the procedure is still nec-essary for other cases

Data Availability

4e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

4e authors declare that they have no conflicts of interest

Acknowledgments

4is work was supported by the National Natural ScienceFoundation of China (contract nos 51804099 51774111 and51704098) the Key Scientific Research Project Fund ofColleges and Universities of Henan Province (19A440011and 19A130001) the Natural Science Foundation of HenanPolytechnic University (B2018-4 and B2018-65) and theRegional Collaborative Innovation Project of the XinjiangUygur Autonomous Region (2017E0292)

References

[1] P K Mandal R Singh J Maiti A K Singh R Kumar andA Sinha ldquoUnderpinning-based simultaneous extraction ofcontiguous sections of a thick coal seam under weak andlaminated partingrdquo International Journal of Rock Mechanicsand Mining Sciences vol 45 no 1 pp 11ndash28 2008

[2] M Colwell D Hill and R Frith ldquoALTS II a longwallgateroad design methodology for Australian collieriesrdquo inProceedings of the First Australasian Ground Control inMining Conference Sydney NSW Australia August 2003

[3] M Shabanimashcool and C C Li ldquoNumerical modelling oflongwall mining and stability analysis of the gates in a coalminerdquo International Journal of Rock Mechanics and MiningSciences vol 51 pp 24ndash34 2012

[4] Y Chen S Q Ma and Y Yu ldquoStability control of un-derground roadways subjected to stresses caused by extrac-tion of a 10-m-thick coal seam a case studyrdquo Rock Mechanicsand Rock Engineering vol 50 no 9 pp 1ndash10 2017

[5] M Colwell R Frith and C Mark ldquoAnalysis of longwalltailgate serviceability (ALTS) a chain pillar design method-ology for Australian conditionsrdquo in Proceedings of the SecondInternational Workshop on Coal Pillar Mechanics and Designpp 33ndash48 1999

[6] J B Bai and C J Hou ldquoNumerical simulation study onstability of narrow coal pillar of roadway driving along goafrdquoChinese Journal of Rock Mechanics and Engineering vol 23no 20 pp 3475ndash3479 2004

[7] E Jirankova V Petros and J Sancer ldquo4e assessment ofstress in an exploited rock mass based on the disturbance ofthe rigid overlying stratardquo International Journal of RockMechanics and Mining Sciences vol 50 pp 77ndash82 2012

[8] G Zhang Y Tan S Liang and H Jia ldquoNumerical estimationof suitable gob-side filling wall width in a highly gassylongwall mining panelrdquo International Journal of Geo-mechanics vol 18 no 8 article 04018091 2018

[9] G Zhang S Liang Y Tan F X Xie S Chen and H JialdquoNumerical modeling for longwall pillar design a case studyfrom a typical longwall panel in Chinardquo Journal of Geophysicsand Engineering vol 15 no 1 pp 121ndash134 2018

[10] E Esterhuizen C Mark and M M Murphy ldquoNumericalmodel calibration for simulating coal pillars gob and over-burden responserdquo in Proceedings of the Twenty-Ninth In-ternational Conference on Ground Control in Miningpp 46ndash57 Morgantown WV USA July 2010

[11] W F Li J B Bai S Peng X Y Wang and Y Xu ldquoNumericalmodeling for yield pillar design a case studyrdquo RockMechanicsand Rock Engineering vol 48 no 1 pp 305ndash318 2014

10 Advances in Civil Engineering

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

Advances in Civil Engineering 11

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Submit your manuscripts atwwwhindawicom

3 Results

31 Activation Characteristics of the Roof above the GobAs the pictures shown in Figure 5 the suspended roofencounters bending fracture and caving activation whenthe suspended area is large enough During the roof acti-vation the cantilever construction supports overburdenloads behind the coal body until it occurs fracture or cavingdown As shown in Figure 5(h) the cantilever constructionencounters fracture above the stiff coal pillar when applyingthe additional vertical stress in the top physical model Asshown in Figures 5(i)ndash5(k) the upper hard roof for instancethe fine sandstone which is strong enough to bear theoverburden loads is called the key stratum [36] is not cavingduring the longwall retreating in Panel 1 However as shownin Figure 5(l) it encounters fracture and caving activationwhen applying the additional vertical stress in the topphysical model

Along the vertical direction roof bends down in thelower roof near the gob initially and then the upper roof

begins to bend down gradually 4e lower roof is larger thanthe upper roof in vertical displacement distinctly As theincreasing distance from the gob center the roof verticaldisplacement decreases gradually as the measuring datashown in Figure 6(a) When the suspended area is largeenough the roof encounters fracture activation in-stantaneously and then cave activation in a short time asshown in Figure 6(b) However the soft stratum such as themudstone group encounters fracture and cave as long as thelower hard roof like the limestone fractures and caves As theincrease of the suspended area the roof encounters thefracture and caving activation and the increasing cavingzone compacts the gob gradually as shown from Figure 6(b)to Figure 6(e)

32 Evolution of the Additional Abutment Stress At firstadditional abutment stress increases slowly then decreasessharply and presents stabilization finally in P1 P2 and P3 asshown in Figures 7(a)ndash7(c)4e stable value is less than zero

Table 1 Materials used in the physical model

Lithology UCS of prototype(MPa)

UCS of model(kPa) Sand (kg) Calcium carbonate (kg) Gypsum (kg) Amounts (kg) Water (L)

Mudstone group 1 3527 14406 7031 703 703 8438 938Medium sandstone 7009 28630 15820 1582 3691 21094 2344Mudstone group 2 3527 14406 58594 5859 5859 70313 7813Fine sandstone 7461 30481 18984 1898 4430 25313 3616Mudstone group 3 3527 14406 38672 3867 3867 46406 5156Limestone 7183 29342 14238 1424 3322 18984 2712Coal seam 15 2483 10141 7998 571 571 9141 1016Mudstone 2971 12135 12054 1004 1004 14063 1563

P1 P2 P3

P5 P4

P6

Miniature pressure cell

Mudstone group

Mudstone group

Unit cm

Fine sandstone

Limestone

Acoustic emission sensor

S1 and S5

S2 and S6 S3 and S7

S4 and S8

375045

00

3000 3000 3000

5000

110

00

3500

1875

3000

343835

00

25000

Measuringline 1

Measuringline 2

Measuringline 3

Measuringline 4

Measuringline 5

Measuringline 6

Medium sandstone

Monitoring point of displacement

Figure 4 Monitoring programme in the physical model

Advances in Civil Engineering 5

Besides applying additional vertical stress in the top modelis independent of the additional abutment stress in P1 P2and P3 Peaks of the additional abutment stress in P2 and P3are larger than that in P1 and the inflection point occurswhen the coal is mined out above the measuring point Inaddition at first the additional abutment stress increasesslowly then increases sharply decreases sharply afterwardsand presents stabilization in the final in P4 P5 and P6 asshown in Figures 7(d)ndash7(f) Additional abutment stress in P5is larger than that in P4 and P6 in amplification and whoseminimum is in P4 However applying additional verticalstress in the top of the model can increase the abutmentstress in P4 P5 and P6 greatly

33 Characteristics of the Acoustic Emission SignalsDistinct acoustic emission phenomenon occurs during thehard roof activation above the gob as measuring point S4 inFigure 8 4e ring count indicates that the number of the

effective acoustic emission signals exceeds the thresholdvalue Obviously the ring count turns to the saltation stateinstantaneously during the layered caving and cantileverconstruction fracture but it always equals to zero when theroof is relatively stable as shown in Figure 8(a) 4e peak ofthe ring count occurs when applying the additional verticalstress in the top of the model 4e energy the area of thedetection signal envelope reflects the strength of theacoustic emission signal As shown in Figure 8(b) the ringcount turns to the saltation state instantaneously whenlayered caving and cantilever construction fracture occurbut it always equals to zero when the roof is relatively stableWhen additional vertical stress is applied the energymonitored is much greater than that in other time In ad-dition the amplitude the range of the acoustic emissionwave envelope is messy but is relatively large during thehard roof activation above the gob as shown in Figure 8(c)Similarly it reaches the peak when applying the additionalvertical stress in the top of the model

(a) (b) (c)

(d) (e) (f )

(g) (h) (i)

(j) (k) (l)

Figure 5 Roof activation characteristics (a) Roof bending (b) Roof fracture (c) Roof caving (d) Cantilever construction (e) Cantileverconstruction fracture (f ) Cantilever construction caving (g) Cantilever construction (h) Cantilever construction fracture (i) Upper roofcondition (j) Suspended upper roof (k) Upper roof fracture (l) Upper roof fracture and caving

6 Advances in Civil Engineering

0 200 400 600 800 1000ndash12

ndash09

ndash06

ndash03

00

Boundary

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundaryEntry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(a)

0 200 400 600 800 1000ndash25

ndash20

ndash15

ndash10

ndash05

00

Caving

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundary

Boundary

Entry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(b)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Outlier Fracture

Gob boundary

Caving

Entry

Caving down

Bend down

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Boundary

(c)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving

Boundary

Caving down

Outlier

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

Entry

(d)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Fracture

Caving

Caving down

Entry

Boundary

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

(e)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving down

EntryCaving

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

BoundaryBend down

(f )

Figure 6 Vertical displacement of the roofs above the gob (a) Panel 1 retreating 500mm (b) Panel 1 retreating 650mm (c) Panel 1retreating 1150mm (d) Panel 1 retreating 1200mm (e) Panel 1 retreating 1600mm (f) Applying additional abutment stress

Advances in Civil Engineering 7

4 Discussion

In mining excavation stiff coal-pillar entry retaining isunder the condition of strong mine ground pressure which

is validated by the physical method 4e rock around theretained entry experiences not only the evolution of the sideabutment stress and the front abutment stress [37] but alsothe loading of dynamic stress induced from the fracture and

0 5 10 15 20 25 30ndash4

ndash3

ndash2

ndash1

0

1

Appling additionalvertical stress

Increasing

DecreasingStabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P1

50

P1 is in the gob floor

(a)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P2

50

P2 is in the gob floor

(b)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P3

50

P3 is in the gob

(c)

0 5 10 15 20 25 300

5

10

15

20

25

Increasing sharply

Stabilization

Peak

Increasing slowly

Applying additional vertical stress

P4 is in the solid coal

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P4

50

(d)

0 5 10 15 20 25 300

10

20

30

40

50

60

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P5 is in the stiff coal pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P5

50

(e)

0 5 10 15 20 25 300

10

20

30

40

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P6 is in the hard roof above the pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P6

50

(f )

Figure 7 Additional abutment stress evolution during the hard roof activation above the gob (a) Measuring point of P1 (b) Measuringpoint of P2 (c) Measuring point of P3 (d) Measuring point of P4 (e) Measuring point of P5 (f ) Measuring point of P6

8 Advances in Civil Engineering

caving activation for the hard roof When the strength andthe stiffness are insufficient to support the overburden loadsthe hard roof structure experiences fracture and cavingactivation like the limestone shown in Figure 5 4e cu-mulative energy of elastic deformation in the structuremay release the dynamic stress instantaneously [38] Whenthe dynamic stress waves to the underground space likethe retained entry dynamic disasters such as the large

deformation in short time occur even if the retained entry isprotected with a stiff coal pillar such as deformation resultsof the retained entry shown in Figure 9

4e suspended roof encounters bending fracture andcaving activation when the suspended area is largeenough During the activation process overlying loadsabove the worked-out area have a loading effect on theunworked-out area Besides the generating dynamic

0 5 10 15 20 25 30 35

0

1000

2000

3000

4000

Retreating distance of panel 1 (cm)Ri

ng co

unt (

time)

Time (times1000s)S4

0 25 50 65 115 160

Layered caving

Cantilever construction fracture

Applying additional vertical stress

(a)

S4

ndash5 0 5 10 15 20 25 30 35ndash10000

0

10000

20000

30000

40000

50000

60000

70000

ndash5 0 5 10 15 20 250

400

800

1200

1600

2000

Constructionfracture

Layered caving

Retreating distance of panel 1 (cm)

Ener

gy (u

vmiddotm

s)

Time (times1000s)

Applying additional vertical stress

0 25 50 65 115 160

0 25 50 65 115

(b)

ndash5 0 5 10 15 20 25 30 3520

40

60

80

100

Retreating distance of panel 1 (cm)

Am

plitu

de (d

B)

Time (times1000s)

0 25 50 65 115 160

Average 3798dB

S4

(c)

Figure 8 Acoustic emission signals during the activation of the hard roof above the gob (a) Ring count in measuring point S4 (b) Energiesin measuring point S4 (c) Amplitude in measuring point S4

Figure 9 Deformation characteristics of the 195m stiff coal-pillar entry retaining [39] 4e entry experiences the whole hard roofactivation above the gob

Advances in Civil Engineering 9

stress wave to the nearby retained entry which makes therock around the retained entry under the synergy effect ofabutment stress and dynamic stress 4e results of miningground pressure in the physical model of plane stress canclearly illustrate the mechanical behavior of the rockaround the retained entry with stiff coal pillar under thehard roof [40]

However the physical model can only simulate themechanical behavior of the rock strata behind the workingface during the mining process when it is under the plane-stress condition When there are several hard roofs nearthe mining coal seam this experimental method is a greatoption for predicting the mine ground pressure of the stiffcoal-pillar entry retaining while it is inappropriate forpredicting the deformation behavior of the retained entrywhen the dimension of the entry is just 31mm in widthand 25mm in height In addition when monitoring thedynamic stress induced from the hard roof activationthe monitoring system of high-frequency pressure cell ismore convinced than vibration signals with the acousticemission

5 Conclusions

In order to reveal the mine ground pressure of stiff coal-pillar entry retaining and verify whether this entry can beretained to serve the next panel influenced by the hard roofactivation a 2D physical model with plane-stress conditionswas established to simulate the mechanical behavior of hardroofs behind the working face 4e results of the experi-mental method are concluded as follows

(1) 4e hard roof closed to the gob undergoes bendingdown fracture and caving activation successivelyunless its upper hard roof is strong enough tosupport overlying loads 4e cantilever structurewhich is supported by the stiff coal pillar above thegob faces the potential fracture activation above thestiff coal pillar under the front abutment stress in-duced from the retreating of the next panel

(2) Under the synergistic effects of the side varyingabutment stress and dynamic stress the entrycannot be retained to serve next panel successfullyeven though it is protected with a stiff coal pillarOverlying loads above the worked-out area mainlyhave a loading effect in the stiff coal pillar Besidesthe dynamic stress induced from the hard roofactivation can wave to the underneath retainedentry

(3) 4e experimental method can be used to analyze themechanical behavior of the rock strata during themining process Since the geological and engineeringconditions are different the procedure is still nec-essary for other cases

Data Availability

4e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

4e authors declare that they have no conflicts of interest

Acknowledgments

4is work was supported by the National Natural ScienceFoundation of China (contract nos 51804099 51774111 and51704098) the Key Scientific Research Project Fund ofColleges and Universities of Henan Province (19A440011and 19A130001) the Natural Science Foundation of HenanPolytechnic University (B2018-4 and B2018-65) and theRegional Collaborative Innovation Project of the XinjiangUygur Autonomous Region (2017E0292)

References

[1] P K Mandal R Singh J Maiti A K Singh R Kumar andA Sinha ldquoUnderpinning-based simultaneous extraction ofcontiguous sections of a thick coal seam under weak andlaminated partingrdquo International Journal of Rock Mechanicsand Mining Sciences vol 45 no 1 pp 11ndash28 2008

[2] M Colwell D Hill and R Frith ldquoALTS II a longwallgateroad design methodology for Australian collieriesrdquo inProceedings of the First Australasian Ground Control inMining Conference Sydney NSW Australia August 2003

[3] M Shabanimashcool and C C Li ldquoNumerical modelling oflongwall mining and stability analysis of the gates in a coalminerdquo International Journal of Rock Mechanics and MiningSciences vol 51 pp 24ndash34 2012

[4] Y Chen S Q Ma and Y Yu ldquoStability control of un-derground roadways subjected to stresses caused by extrac-tion of a 10-m-thick coal seam a case studyrdquo Rock Mechanicsand Rock Engineering vol 50 no 9 pp 1ndash10 2017

[5] M Colwell R Frith and C Mark ldquoAnalysis of longwalltailgate serviceability (ALTS) a chain pillar design method-ology for Australian conditionsrdquo in Proceedings of the SecondInternational Workshop on Coal Pillar Mechanics and Designpp 33ndash48 1999

[6] J B Bai and C J Hou ldquoNumerical simulation study onstability of narrow coal pillar of roadway driving along goafrdquoChinese Journal of Rock Mechanics and Engineering vol 23no 20 pp 3475ndash3479 2004

[7] E Jirankova V Petros and J Sancer ldquo4e assessment ofstress in an exploited rock mass based on the disturbance ofthe rigid overlying stratardquo International Journal of RockMechanics and Mining Sciences vol 50 pp 77ndash82 2012

[8] G Zhang Y Tan S Liang and H Jia ldquoNumerical estimationof suitable gob-side filling wall width in a highly gassylongwall mining panelrdquo International Journal of Geo-mechanics vol 18 no 8 article 04018091 2018

[9] G Zhang S Liang Y Tan F X Xie S Chen and H JialdquoNumerical modeling for longwall pillar design a case studyfrom a typical longwall panel in Chinardquo Journal of Geophysicsand Engineering vol 15 no 1 pp 121ndash134 2018

[10] E Esterhuizen C Mark and M M Murphy ldquoNumericalmodel calibration for simulating coal pillars gob and over-burden responserdquo in Proceedings of the Twenty-Ninth In-ternational Conference on Ground Control in Miningpp 46ndash57 Morgantown WV USA July 2010

[11] W F Li J B Bai S Peng X Y Wang and Y Xu ldquoNumericalmodeling for yield pillar design a case studyrdquo RockMechanicsand Rock Engineering vol 48 no 1 pp 305ndash318 2014

10 Advances in Civil Engineering

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

Advances in Civil Engineering 11

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Submit your manuscripts atwwwhindawicom

Besides applying additional vertical stress in the top modelis independent of the additional abutment stress in P1 P2and P3 Peaks of the additional abutment stress in P2 and P3are larger than that in P1 and the inflection point occurswhen the coal is mined out above the measuring point Inaddition at first the additional abutment stress increasesslowly then increases sharply decreases sharply afterwardsand presents stabilization in the final in P4 P5 and P6 asshown in Figures 7(d)ndash7(f) Additional abutment stress in P5is larger than that in P4 and P6 in amplification and whoseminimum is in P4 However applying additional verticalstress in the top of the model can increase the abutmentstress in P4 P5 and P6 greatly

33 Characteristics of the Acoustic Emission SignalsDistinct acoustic emission phenomenon occurs during thehard roof activation above the gob as measuring point S4 inFigure 8 4e ring count indicates that the number of the

effective acoustic emission signals exceeds the thresholdvalue Obviously the ring count turns to the saltation stateinstantaneously during the layered caving and cantileverconstruction fracture but it always equals to zero when theroof is relatively stable as shown in Figure 8(a) 4e peak ofthe ring count occurs when applying the additional verticalstress in the top of the model 4e energy the area of thedetection signal envelope reflects the strength of theacoustic emission signal As shown in Figure 8(b) the ringcount turns to the saltation state instantaneously whenlayered caving and cantilever construction fracture occurbut it always equals to zero when the roof is relatively stableWhen additional vertical stress is applied the energymonitored is much greater than that in other time In ad-dition the amplitude the range of the acoustic emissionwave envelope is messy but is relatively large during thehard roof activation above the gob as shown in Figure 8(c)Similarly it reaches the peak when applying the additionalvertical stress in the top of the model

(a) (b) (c)

(d) (e) (f )

(g) (h) (i)

(j) (k) (l)

Figure 5 Roof activation characteristics (a) Roof bending (b) Roof fracture (c) Roof caving (d) Cantilever construction (e) Cantileverconstruction fracture (f ) Cantilever construction caving (g) Cantilever construction (h) Cantilever construction fracture (i) Upper roofcondition (j) Suspended upper roof (k) Upper roof fracture (l) Upper roof fracture and caving

6 Advances in Civil Engineering

0 200 400 600 800 1000ndash12

ndash09

ndash06

ndash03

00

Boundary

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundaryEntry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(a)

0 200 400 600 800 1000ndash25

ndash20

ndash15

ndash10

ndash05

00

Caving

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundary

Boundary

Entry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(b)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Outlier Fracture

Gob boundary

Caving

Entry

Caving down

Bend down

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Boundary

(c)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving

Boundary

Caving down

Outlier

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

Entry

(d)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Fracture

Caving

Caving down

Entry

Boundary

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

(e)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving down

EntryCaving

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

BoundaryBend down

(f )

Figure 6 Vertical displacement of the roofs above the gob (a) Panel 1 retreating 500mm (b) Panel 1 retreating 650mm (c) Panel 1retreating 1150mm (d) Panel 1 retreating 1200mm (e) Panel 1 retreating 1600mm (f) Applying additional abutment stress

Advances in Civil Engineering 7

4 Discussion

In mining excavation stiff coal-pillar entry retaining isunder the condition of strong mine ground pressure which

is validated by the physical method 4e rock around theretained entry experiences not only the evolution of the sideabutment stress and the front abutment stress [37] but alsothe loading of dynamic stress induced from the fracture and

0 5 10 15 20 25 30ndash4

ndash3

ndash2

ndash1

0

1

Appling additionalvertical stress

Increasing

DecreasingStabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P1

50

P1 is in the gob floor

(a)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P2

50

P2 is in the gob floor

(b)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P3

50

P3 is in the gob

(c)

0 5 10 15 20 25 300

5

10

15

20

25

Increasing sharply

Stabilization

Peak

Increasing slowly

Applying additional vertical stress

P4 is in the solid coal

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P4

50

(d)

0 5 10 15 20 25 300

10

20

30

40

50

60

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P5 is in the stiff coal pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P5

50

(e)

0 5 10 15 20 25 300

10

20

30

40

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P6 is in the hard roof above the pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P6

50

(f )

Figure 7 Additional abutment stress evolution during the hard roof activation above the gob (a) Measuring point of P1 (b) Measuringpoint of P2 (c) Measuring point of P3 (d) Measuring point of P4 (e) Measuring point of P5 (f ) Measuring point of P6

8 Advances in Civil Engineering

caving activation for the hard roof When the strength andthe stiffness are insufficient to support the overburden loadsthe hard roof structure experiences fracture and cavingactivation like the limestone shown in Figure 5 4e cu-mulative energy of elastic deformation in the structuremay release the dynamic stress instantaneously [38] Whenthe dynamic stress waves to the underground space likethe retained entry dynamic disasters such as the large

deformation in short time occur even if the retained entry isprotected with a stiff coal pillar such as deformation resultsof the retained entry shown in Figure 9

4e suspended roof encounters bending fracture andcaving activation when the suspended area is largeenough During the activation process overlying loadsabove the worked-out area have a loading effect on theunworked-out area Besides the generating dynamic

0 5 10 15 20 25 30 35

0

1000

2000

3000

4000

Retreating distance of panel 1 (cm)Ri

ng co

unt (

time)

Time (times1000s)S4

0 25 50 65 115 160

Layered caving

Cantilever construction fracture

Applying additional vertical stress

(a)

S4

ndash5 0 5 10 15 20 25 30 35ndash10000

0

10000

20000

30000

40000

50000

60000

70000

ndash5 0 5 10 15 20 250

400

800

1200

1600

2000

Constructionfracture

Layered caving

Retreating distance of panel 1 (cm)

Ener

gy (u

vmiddotm

s)

Time (times1000s)

Applying additional vertical stress

0 25 50 65 115 160

0 25 50 65 115

(b)

ndash5 0 5 10 15 20 25 30 3520

40

60

80

100

Retreating distance of panel 1 (cm)

Am

plitu

de (d

B)

Time (times1000s)

0 25 50 65 115 160

Average 3798dB

S4

(c)

Figure 8 Acoustic emission signals during the activation of the hard roof above the gob (a) Ring count in measuring point S4 (b) Energiesin measuring point S4 (c) Amplitude in measuring point S4

Figure 9 Deformation characteristics of the 195m stiff coal-pillar entry retaining [39] 4e entry experiences the whole hard roofactivation above the gob

Advances in Civil Engineering 9

stress wave to the nearby retained entry which makes therock around the retained entry under the synergy effect ofabutment stress and dynamic stress 4e results of miningground pressure in the physical model of plane stress canclearly illustrate the mechanical behavior of the rockaround the retained entry with stiff coal pillar under thehard roof [40]

However the physical model can only simulate themechanical behavior of the rock strata behind the workingface during the mining process when it is under the plane-stress condition When there are several hard roofs nearthe mining coal seam this experimental method is a greatoption for predicting the mine ground pressure of the stiffcoal-pillar entry retaining while it is inappropriate forpredicting the deformation behavior of the retained entrywhen the dimension of the entry is just 31mm in widthand 25mm in height In addition when monitoring thedynamic stress induced from the hard roof activationthe monitoring system of high-frequency pressure cell ismore convinced than vibration signals with the acousticemission

5 Conclusions

In order to reveal the mine ground pressure of stiff coal-pillar entry retaining and verify whether this entry can beretained to serve the next panel influenced by the hard roofactivation a 2D physical model with plane-stress conditionswas established to simulate the mechanical behavior of hardroofs behind the working face 4e results of the experi-mental method are concluded as follows

(1) 4e hard roof closed to the gob undergoes bendingdown fracture and caving activation successivelyunless its upper hard roof is strong enough tosupport overlying loads 4e cantilever structurewhich is supported by the stiff coal pillar above thegob faces the potential fracture activation above thestiff coal pillar under the front abutment stress in-duced from the retreating of the next panel

(2) Under the synergistic effects of the side varyingabutment stress and dynamic stress the entrycannot be retained to serve next panel successfullyeven though it is protected with a stiff coal pillarOverlying loads above the worked-out area mainlyhave a loading effect in the stiff coal pillar Besidesthe dynamic stress induced from the hard roofactivation can wave to the underneath retainedentry

(3) 4e experimental method can be used to analyze themechanical behavior of the rock strata during themining process Since the geological and engineeringconditions are different the procedure is still nec-essary for other cases

Data Availability

4e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

4e authors declare that they have no conflicts of interest

Acknowledgments

4is work was supported by the National Natural ScienceFoundation of China (contract nos 51804099 51774111 and51704098) the Key Scientific Research Project Fund ofColleges and Universities of Henan Province (19A440011and 19A130001) the Natural Science Foundation of HenanPolytechnic University (B2018-4 and B2018-65) and theRegional Collaborative Innovation Project of the XinjiangUygur Autonomous Region (2017E0292)

References

[1] P K Mandal R Singh J Maiti A K Singh R Kumar andA Sinha ldquoUnderpinning-based simultaneous extraction ofcontiguous sections of a thick coal seam under weak andlaminated partingrdquo International Journal of Rock Mechanicsand Mining Sciences vol 45 no 1 pp 11ndash28 2008

[2] M Colwell D Hill and R Frith ldquoALTS II a longwallgateroad design methodology for Australian collieriesrdquo inProceedings of the First Australasian Ground Control inMining Conference Sydney NSW Australia August 2003

[3] M Shabanimashcool and C C Li ldquoNumerical modelling oflongwall mining and stability analysis of the gates in a coalminerdquo International Journal of Rock Mechanics and MiningSciences vol 51 pp 24ndash34 2012

[4] Y Chen S Q Ma and Y Yu ldquoStability control of un-derground roadways subjected to stresses caused by extrac-tion of a 10-m-thick coal seam a case studyrdquo Rock Mechanicsand Rock Engineering vol 50 no 9 pp 1ndash10 2017

[5] M Colwell R Frith and C Mark ldquoAnalysis of longwalltailgate serviceability (ALTS) a chain pillar design method-ology for Australian conditionsrdquo in Proceedings of the SecondInternational Workshop on Coal Pillar Mechanics and Designpp 33ndash48 1999

[6] J B Bai and C J Hou ldquoNumerical simulation study onstability of narrow coal pillar of roadway driving along goafrdquoChinese Journal of Rock Mechanics and Engineering vol 23no 20 pp 3475ndash3479 2004

[7] E Jirankova V Petros and J Sancer ldquo4e assessment ofstress in an exploited rock mass based on the disturbance ofthe rigid overlying stratardquo International Journal of RockMechanics and Mining Sciences vol 50 pp 77ndash82 2012

[8] G Zhang Y Tan S Liang and H Jia ldquoNumerical estimationof suitable gob-side filling wall width in a highly gassylongwall mining panelrdquo International Journal of Geo-mechanics vol 18 no 8 article 04018091 2018

[9] G Zhang S Liang Y Tan F X Xie S Chen and H JialdquoNumerical modeling for longwall pillar design a case studyfrom a typical longwall panel in Chinardquo Journal of Geophysicsand Engineering vol 15 no 1 pp 121ndash134 2018

[10] E Esterhuizen C Mark and M M Murphy ldquoNumericalmodel calibration for simulating coal pillars gob and over-burden responserdquo in Proceedings of the Twenty-Ninth In-ternational Conference on Ground Control in Miningpp 46ndash57 Morgantown WV USA July 2010

[11] W F Li J B Bai S Peng X Y Wang and Y Xu ldquoNumericalmodeling for yield pillar design a case studyrdquo RockMechanicsand Rock Engineering vol 48 no 1 pp 305ndash318 2014

10 Advances in Civil Engineering

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

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

0 200 400 600 800 1000ndash12

ndash09

ndash06

ndash03

00

Boundary

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundaryEntry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(a)

0 200 400 600 800 1000ndash25

ndash20

ndash15

ndash10

ndash05

00

Caving

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Gob boundary

Boundary

Entry

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

(b)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Outlier Fracture

Gob boundary

Caving

Entry

Caving down

Bend down

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Boundary

(c)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving

Boundary

Caving down

Outlier

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

Entry

(d)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Fracture

Caving

Caving down

Entry

Boundary

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

Bend down

Gob boundary

(e)

Measuring line 1Measuring line 2Measuring line 3

Measuring line 4Measuring line 5Measuring line 6

0 200 400 600 800 1000ndash80

ndash60

ndash40

ndash20

0

Caving down

EntryCaving

Fracture

Roof

ver

tical

disp

lace

men

t (m

m)

Distance from the gob center (mm)

BoundaryBend down

(f )

Figure 6 Vertical displacement of the roofs above the gob (a) Panel 1 retreating 500mm (b) Panel 1 retreating 650mm (c) Panel 1retreating 1150mm (d) Panel 1 retreating 1200mm (e) Panel 1 retreating 1600mm (f) Applying additional abutment stress

Advances in Civil Engineering 7

4 Discussion

In mining excavation stiff coal-pillar entry retaining isunder the condition of strong mine ground pressure which

is validated by the physical method 4e rock around theretained entry experiences not only the evolution of the sideabutment stress and the front abutment stress [37] but alsothe loading of dynamic stress induced from the fracture and

0 5 10 15 20 25 30ndash4

ndash3

ndash2

ndash1

0

1

Appling additionalvertical stress

Increasing

DecreasingStabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P1

50

P1 is in the gob floor

(a)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P2

50

P2 is in the gob floor

(b)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P3

50

P3 is in the gob

(c)

0 5 10 15 20 25 300

5

10

15

20

25

Increasing sharply

Stabilization

Peak

Increasing slowly

Applying additional vertical stress

P4 is in the solid coal

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P4

50

(d)

0 5 10 15 20 25 300

10

20

30

40

50

60

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P5 is in the stiff coal pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P5

50

(e)

0 5 10 15 20 25 300

10

20

30

40

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P6 is in the hard roof above the pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P6

50

(f )

Figure 7 Additional abutment stress evolution during the hard roof activation above the gob (a) Measuring point of P1 (b) Measuringpoint of P2 (c) Measuring point of P3 (d) Measuring point of P4 (e) Measuring point of P5 (f ) Measuring point of P6

8 Advances in Civil Engineering

caving activation for the hard roof When the strength andthe stiffness are insufficient to support the overburden loadsthe hard roof structure experiences fracture and cavingactivation like the limestone shown in Figure 5 4e cu-mulative energy of elastic deformation in the structuremay release the dynamic stress instantaneously [38] Whenthe dynamic stress waves to the underground space likethe retained entry dynamic disasters such as the large

deformation in short time occur even if the retained entry isprotected with a stiff coal pillar such as deformation resultsof the retained entry shown in Figure 9

4e suspended roof encounters bending fracture andcaving activation when the suspended area is largeenough During the activation process overlying loadsabove the worked-out area have a loading effect on theunworked-out area Besides the generating dynamic

0 5 10 15 20 25 30 35

0

1000

2000

3000

4000

Retreating distance of panel 1 (cm)Ri

ng co

unt (

time)

Time (times1000s)S4

0 25 50 65 115 160

Layered caving

Cantilever construction fracture

Applying additional vertical stress

(a)

S4

ndash5 0 5 10 15 20 25 30 35ndash10000

0

10000

20000

30000

40000

50000

60000

70000

ndash5 0 5 10 15 20 250

400

800

1200

1600

2000

Constructionfracture

Layered caving

Retreating distance of panel 1 (cm)

Ener

gy (u

vmiddotm

s)

Time (times1000s)

Applying additional vertical stress

0 25 50 65 115 160

0 25 50 65 115

(b)

ndash5 0 5 10 15 20 25 30 3520

40

60

80

100

Retreating distance of panel 1 (cm)

Am

plitu

de (d

B)

Time (times1000s)

0 25 50 65 115 160

Average 3798dB

S4

(c)

Figure 8 Acoustic emission signals during the activation of the hard roof above the gob (a) Ring count in measuring point S4 (b) Energiesin measuring point S4 (c) Amplitude in measuring point S4

Figure 9 Deformation characteristics of the 195m stiff coal-pillar entry retaining [39] 4e entry experiences the whole hard roofactivation above the gob

Advances in Civil Engineering 9

stress wave to the nearby retained entry which makes therock around the retained entry under the synergy effect ofabutment stress and dynamic stress 4e results of miningground pressure in the physical model of plane stress canclearly illustrate the mechanical behavior of the rockaround the retained entry with stiff coal pillar under thehard roof [40]

However the physical model can only simulate themechanical behavior of the rock strata behind the workingface during the mining process when it is under the plane-stress condition When there are several hard roofs nearthe mining coal seam this experimental method is a greatoption for predicting the mine ground pressure of the stiffcoal-pillar entry retaining while it is inappropriate forpredicting the deformation behavior of the retained entrywhen the dimension of the entry is just 31mm in widthand 25mm in height In addition when monitoring thedynamic stress induced from the hard roof activationthe monitoring system of high-frequency pressure cell ismore convinced than vibration signals with the acousticemission

5 Conclusions

In order to reveal the mine ground pressure of stiff coal-pillar entry retaining and verify whether this entry can beretained to serve the next panel influenced by the hard roofactivation a 2D physical model with plane-stress conditionswas established to simulate the mechanical behavior of hardroofs behind the working face 4e results of the experi-mental method are concluded as follows

(1) 4e hard roof closed to the gob undergoes bendingdown fracture and caving activation successivelyunless its upper hard roof is strong enough tosupport overlying loads 4e cantilever structurewhich is supported by the stiff coal pillar above thegob faces the potential fracture activation above thestiff coal pillar under the front abutment stress in-duced from the retreating of the next panel

(2) Under the synergistic effects of the side varyingabutment stress and dynamic stress the entrycannot be retained to serve next panel successfullyeven though it is protected with a stiff coal pillarOverlying loads above the worked-out area mainlyhave a loading effect in the stiff coal pillar Besidesthe dynamic stress induced from the hard roofactivation can wave to the underneath retainedentry

(3) 4e experimental method can be used to analyze themechanical behavior of the rock strata during themining process Since the geological and engineeringconditions are different the procedure is still nec-essary for other cases

Data Availability

4e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

4e authors declare that they have no conflicts of interest

Acknowledgments

4is work was supported by the National Natural ScienceFoundation of China (contract nos 51804099 51774111 and51704098) the Key Scientific Research Project Fund ofColleges and Universities of Henan Province (19A440011and 19A130001) the Natural Science Foundation of HenanPolytechnic University (B2018-4 and B2018-65) and theRegional Collaborative Innovation Project of the XinjiangUygur Autonomous Region (2017E0292)

References

[1] P K Mandal R Singh J Maiti A K Singh R Kumar andA Sinha ldquoUnderpinning-based simultaneous extraction ofcontiguous sections of a thick coal seam under weak andlaminated partingrdquo International Journal of Rock Mechanicsand Mining Sciences vol 45 no 1 pp 11ndash28 2008

[2] M Colwell D Hill and R Frith ldquoALTS II a longwallgateroad design methodology for Australian collieriesrdquo inProceedings of the First Australasian Ground Control inMining Conference Sydney NSW Australia August 2003

[3] M Shabanimashcool and C C Li ldquoNumerical modelling oflongwall mining and stability analysis of the gates in a coalminerdquo International Journal of Rock Mechanics and MiningSciences vol 51 pp 24ndash34 2012

[4] Y Chen S Q Ma and Y Yu ldquoStability control of un-derground roadways subjected to stresses caused by extrac-tion of a 10-m-thick coal seam a case studyrdquo Rock Mechanicsand Rock Engineering vol 50 no 9 pp 1ndash10 2017

[5] M Colwell R Frith and C Mark ldquoAnalysis of longwalltailgate serviceability (ALTS) a chain pillar design method-ology for Australian conditionsrdquo in Proceedings of the SecondInternational Workshop on Coal Pillar Mechanics and Designpp 33ndash48 1999

[6] J B Bai and C J Hou ldquoNumerical simulation study onstability of narrow coal pillar of roadway driving along goafrdquoChinese Journal of Rock Mechanics and Engineering vol 23no 20 pp 3475ndash3479 2004

[7] E Jirankova V Petros and J Sancer ldquo4e assessment ofstress in an exploited rock mass based on the disturbance ofthe rigid overlying stratardquo International Journal of RockMechanics and Mining Sciences vol 50 pp 77ndash82 2012

[8] G Zhang Y Tan S Liang and H Jia ldquoNumerical estimationof suitable gob-side filling wall width in a highly gassylongwall mining panelrdquo International Journal of Geo-mechanics vol 18 no 8 article 04018091 2018

[9] G Zhang S Liang Y Tan F X Xie S Chen and H JialdquoNumerical modeling for longwall pillar design a case studyfrom a typical longwall panel in Chinardquo Journal of Geophysicsand Engineering vol 15 no 1 pp 121ndash134 2018

[10] E Esterhuizen C Mark and M M Murphy ldquoNumericalmodel calibration for simulating coal pillars gob and over-burden responserdquo in Proceedings of the Twenty-Ninth In-ternational Conference on Ground Control in Miningpp 46ndash57 Morgantown WV USA July 2010

[11] W F Li J B Bai S Peng X Y Wang and Y Xu ldquoNumericalmodeling for yield pillar design a case studyrdquo RockMechanicsand Rock Engineering vol 48 no 1 pp 305ndash318 2014

10 Advances in Civil Engineering

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

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

4 Discussion

In mining excavation stiff coal-pillar entry retaining isunder the condition of strong mine ground pressure which

is validated by the physical method 4e rock around theretained entry experiences not only the evolution of the sideabutment stress and the front abutment stress [37] but alsothe loading of dynamic stress induced from the fracture and

0 5 10 15 20 25 30ndash4

ndash3

ndash2

ndash1

0

1

Appling additionalvertical stress

Increasing

DecreasingStabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P1

50

P1 is in the gob floor

(a)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P2

50

P2 is in the gob floor

(b)

0 5 10 15 20 25 30ndash3

ndash2

ndash1

0

1

2

3

4

Applying additional vertical stress

Increasing

Decreasing

Stabilization

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P3

50

P3 is in the gob

(c)

0 5 10 15 20 25 300

5

10

15

20

25

Increasing sharply

Stabilization

Peak

Increasing slowly

Applying additional vertical stress

P4 is in the solid coal

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tress

(kPa

)

Time (times1000s)

P4

50

(d)

0 5 10 15 20 25 300

10

20

30

40

50

60

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P5 is in the stiff coal pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P5

50

(e)

0 5 10 15 20 25 300

10

20

30

40

Stabilization

Peak

Increasing sharply

Increasing slowly

Applying additional vertical stress

P6 is in the hard roof above the pillar

1601156525Retreating distance of panel 1 (cm)

Add

ition

al ab

utm

ent s

tres

s (kP

a)

Time (times1000s)

P6

50

(f )

Figure 7 Additional abutment stress evolution during the hard roof activation above the gob (a) Measuring point of P1 (b) Measuringpoint of P2 (c) Measuring point of P3 (d) Measuring point of P4 (e) Measuring point of P5 (f ) Measuring point of P6

8 Advances in Civil Engineering

caving activation for the hard roof When the strength andthe stiffness are insufficient to support the overburden loadsthe hard roof structure experiences fracture and cavingactivation like the limestone shown in Figure 5 4e cu-mulative energy of elastic deformation in the structuremay release the dynamic stress instantaneously [38] Whenthe dynamic stress waves to the underground space likethe retained entry dynamic disasters such as the large

deformation in short time occur even if the retained entry isprotected with a stiff coal pillar such as deformation resultsof the retained entry shown in Figure 9

4e suspended roof encounters bending fracture andcaving activation when the suspended area is largeenough During the activation process overlying loadsabove the worked-out area have a loading effect on theunworked-out area Besides the generating dynamic

0 5 10 15 20 25 30 35

0

1000

2000

3000

4000

Retreating distance of panel 1 (cm)Ri

ng co

unt (

time)

Time (times1000s)S4

0 25 50 65 115 160

Layered caving

Cantilever construction fracture

Applying additional vertical stress

(a)

S4

ndash5 0 5 10 15 20 25 30 35ndash10000

0

10000

20000

30000

40000

50000

60000

70000

ndash5 0 5 10 15 20 250

400

800

1200

1600

2000

Constructionfracture

Layered caving

Retreating distance of panel 1 (cm)

Ener

gy (u

vmiddotm

s)

Time (times1000s)

Applying additional vertical stress

0 25 50 65 115 160

0 25 50 65 115

(b)

ndash5 0 5 10 15 20 25 30 3520

40

60

80

100

Retreating distance of panel 1 (cm)

Am

plitu

de (d

B)

Time (times1000s)

0 25 50 65 115 160

Average 3798dB

S4

(c)

Figure 8 Acoustic emission signals during the activation of the hard roof above the gob (a) Ring count in measuring point S4 (b) Energiesin measuring point S4 (c) Amplitude in measuring point S4

Figure 9 Deformation characteristics of the 195m stiff coal-pillar entry retaining [39] 4e entry experiences the whole hard roofactivation above the gob

Advances in Civil Engineering 9

stress wave to the nearby retained entry which makes therock around the retained entry under the synergy effect ofabutment stress and dynamic stress 4e results of miningground pressure in the physical model of plane stress canclearly illustrate the mechanical behavior of the rockaround the retained entry with stiff coal pillar under thehard roof [40]

However the physical model can only simulate themechanical behavior of the rock strata behind the workingface during the mining process when it is under the plane-stress condition When there are several hard roofs nearthe mining coal seam this experimental method is a greatoption for predicting the mine ground pressure of the stiffcoal-pillar entry retaining while it is inappropriate forpredicting the deformation behavior of the retained entrywhen the dimension of the entry is just 31mm in widthand 25mm in height In addition when monitoring thedynamic stress induced from the hard roof activationthe monitoring system of high-frequency pressure cell ismore convinced than vibration signals with the acousticemission

5 Conclusions

In order to reveal the mine ground pressure of stiff coal-pillar entry retaining and verify whether this entry can beretained to serve the next panel influenced by the hard roofactivation a 2D physical model with plane-stress conditionswas established to simulate the mechanical behavior of hardroofs behind the working face 4e results of the experi-mental method are concluded as follows

(1) 4e hard roof closed to the gob undergoes bendingdown fracture and caving activation successivelyunless its upper hard roof is strong enough tosupport overlying loads 4e cantilever structurewhich is supported by the stiff coal pillar above thegob faces the potential fracture activation above thestiff coal pillar under the front abutment stress in-duced from the retreating of the next panel

(2) Under the synergistic effects of the side varyingabutment stress and dynamic stress the entrycannot be retained to serve next panel successfullyeven though it is protected with a stiff coal pillarOverlying loads above the worked-out area mainlyhave a loading effect in the stiff coal pillar Besidesthe dynamic stress induced from the hard roofactivation can wave to the underneath retainedentry

(3) 4e experimental method can be used to analyze themechanical behavior of the rock strata during themining process Since the geological and engineeringconditions are different the procedure is still nec-essary for other cases

Data Availability

4e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

4e authors declare that they have no conflicts of interest

Acknowledgments

4is work was supported by the National Natural ScienceFoundation of China (contract nos 51804099 51774111 and51704098) the Key Scientific Research Project Fund ofColleges and Universities of Henan Province (19A440011and 19A130001) the Natural Science Foundation of HenanPolytechnic University (B2018-4 and B2018-65) and theRegional Collaborative Innovation Project of the XinjiangUygur Autonomous Region (2017E0292)

References

[1] P K Mandal R Singh J Maiti A K Singh R Kumar andA Sinha ldquoUnderpinning-based simultaneous extraction ofcontiguous sections of a thick coal seam under weak andlaminated partingrdquo International Journal of Rock Mechanicsand Mining Sciences vol 45 no 1 pp 11ndash28 2008

[2] M Colwell D Hill and R Frith ldquoALTS II a longwallgateroad design methodology for Australian collieriesrdquo inProceedings of the First Australasian Ground Control inMining Conference Sydney NSW Australia August 2003

[3] M Shabanimashcool and C C Li ldquoNumerical modelling oflongwall mining and stability analysis of the gates in a coalminerdquo International Journal of Rock Mechanics and MiningSciences vol 51 pp 24ndash34 2012

[4] Y Chen S Q Ma and Y Yu ldquoStability control of un-derground roadways subjected to stresses caused by extrac-tion of a 10-m-thick coal seam a case studyrdquo Rock Mechanicsand Rock Engineering vol 50 no 9 pp 1ndash10 2017

[5] M Colwell R Frith and C Mark ldquoAnalysis of longwalltailgate serviceability (ALTS) a chain pillar design method-ology for Australian conditionsrdquo in Proceedings of the SecondInternational Workshop on Coal Pillar Mechanics and Designpp 33ndash48 1999

[6] J B Bai and C J Hou ldquoNumerical simulation study onstability of narrow coal pillar of roadway driving along goafrdquoChinese Journal of Rock Mechanics and Engineering vol 23no 20 pp 3475ndash3479 2004

[7] E Jirankova V Petros and J Sancer ldquo4e assessment ofstress in an exploited rock mass based on the disturbance ofthe rigid overlying stratardquo International Journal of RockMechanics and Mining Sciences vol 50 pp 77ndash82 2012

[8] G Zhang Y Tan S Liang and H Jia ldquoNumerical estimationof suitable gob-side filling wall width in a highly gassylongwall mining panelrdquo International Journal of Geo-mechanics vol 18 no 8 article 04018091 2018

[9] G Zhang S Liang Y Tan F X Xie S Chen and H JialdquoNumerical modeling for longwall pillar design a case studyfrom a typical longwall panel in Chinardquo Journal of Geophysicsand Engineering vol 15 no 1 pp 121ndash134 2018

[10] E Esterhuizen C Mark and M M Murphy ldquoNumericalmodel calibration for simulating coal pillars gob and over-burden responserdquo in Proceedings of the Twenty-Ninth In-ternational Conference on Ground Control in Miningpp 46ndash57 Morgantown WV USA July 2010

[11] W F Li J B Bai S Peng X Y Wang and Y Xu ldquoNumericalmodeling for yield pillar design a case studyrdquo RockMechanicsand Rock Engineering vol 48 no 1 pp 305ndash318 2014

10 Advances in Civil Engineering

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

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

caving activation for the hard roof When the strength andthe stiffness are insufficient to support the overburden loadsthe hard roof structure experiences fracture and cavingactivation like the limestone shown in Figure 5 4e cu-mulative energy of elastic deformation in the structuremay release the dynamic stress instantaneously [38] Whenthe dynamic stress waves to the underground space likethe retained entry dynamic disasters such as the large

deformation in short time occur even if the retained entry isprotected with a stiff coal pillar such as deformation resultsof the retained entry shown in Figure 9

4e suspended roof encounters bending fracture andcaving activation when the suspended area is largeenough During the activation process overlying loadsabove the worked-out area have a loading effect on theunworked-out area Besides the generating dynamic

0 5 10 15 20 25 30 35

0

1000

2000

3000

4000

Retreating distance of panel 1 (cm)Ri

ng co

unt (

time)

Time (times1000s)S4

0 25 50 65 115 160

Layered caving

Cantilever construction fracture

Applying additional vertical stress

(a)

S4

ndash5 0 5 10 15 20 25 30 35ndash10000

0

10000

20000

30000

40000

50000

60000

70000

ndash5 0 5 10 15 20 250

400

800

1200

1600

2000

Constructionfracture

Layered caving

Retreating distance of panel 1 (cm)

Ener

gy (u

vmiddotm

s)

Time (times1000s)

Applying additional vertical stress

0 25 50 65 115 160

0 25 50 65 115

(b)

ndash5 0 5 10 15 20 25 30 3520

40

60

80

100

Retreating distance of panel 1 (cm)

Am

plitu

de (d

B)

Time (times1000s)

0 25 50 65 115 160

Average 3798dB

S4

(c)

Figure 8 Acoustic emission signals during the activation of the hard roof above the gob (a) Ring count in measuring point S4 (b) Energiesin measuring point S4 (c) Amplitude in measuring point S4

Figure 9 Deformation characteristics of the 195m stiff coal-pillar entry retaining [39] 4e entry experiences the whole hard roofactivation above the gob

Advances in Civil Engineering 9

stress wave to the nearby retained entry which makes therock around the retained entry under the synergy effect ofabutment stress and dynamic stress 4e results of miningground pressure in the physical model of plane stress canclearly illustrate the mechanical behavior of the rockaround the retained entry with stiff coal pillar under thehard roof [40]

However the physical model can only simulate themechanical behavior of the rock strata behind the workingface during the mining process when it is under the plane-stress condition When there are several hard roofs nearthe mining coal seam this experimental method is a greatoption for predicting the mine ground pressure of the stiffcoal-pillar entry retaining while it is inappropriate forpredicting the deformation behavior of the retained entrywhen the dimension of the entry is just 31mm in widthand 25mm in height In addition when monitoring thedynamic stress induced from the hard roof activationthe monitoring system of high-frequency pressure cell ismore convinced than vibration signals with the acousticemission

5 Conclusions

In order to reveal the mine ground pressure of stiff coal-pillar entry retaining and verify whether this entry can beretained to serve the next panel influenced by the hard roofactivation a 2D physical model with plane-stress conditionswas established to simulate the mechanical behavior of hardroofs behind the working face 4e results of the experi-mental method are concluded as follows

(1) 4e hard roof closed to the gob undergoes bendingdown fracture and caving activation successivelyunless its upper hard roof is strong enough tosupport overlying loads 4e cantilever structurewhich is supported by the stiff coal pillar above thegob faces the potential fracture activation above thestiff coal pillar under the front abutment stress in-duced from the retreating of the next panel

(2) Under the synergistic effects of the side varyingabutment stress and dynamic stress the entrycannot be retained to serve next panel successfullyeven though it is protected with a stiff coal pillarOverlying loads above the worked-out area mainlyhave a loading effect in the stiff coal pillar Besidesthe dynamic stress induced from the hard roofactivation can wave to the underneath retainedentry

(3) 4e experimental method can be used to analyze themechanical behavior of the rock strata during themining process Since the geological and engineeringconditions are different the procedure is still nec-essary for other cases

Data Availability

4e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

4e authors declare that they have no conflicts of interest

Acknowledgments

4is work was supported by the National Natural ScienceFoundation of China (contract nos 51804099 51774111 and51704098) the Key Scientific Research Project Fund ofColleges and Universities of Henan Province (19A440011and 19A130001) the Natural Science Foundation of HenanPolytechnic University (B2018-4 and B2018-65) and theRegional Collaborative Innovation Project of the XinjiangUygur Autonomous Region (2017E0292)

References

[1] P K Mandal R Singh J Maiti A K Singh R Kumar andA Sinha ldquoUnderpinning-based simultaneous extraction ofcontiguous sections of a thick coal seam under weak andlaminated partingrdquo International Journal of Rock Mechanicsand Mining Sciences vol 45 no 1 pp 11ndash28 2008

[2] M Colwell D Hill and R Frith ldquoALTS II a longwallgateroad design methodology for Australian collieriesrdquo inProceedings of the First Australasian Ground Control inMining Conference Sydney NSW Australia August 2003

[3] M Shabanimashcool and C C Li ldquoNumerical modelling oflongwall mining and stability analysis of the gates in a coalminerdquo International Journal of Rock Mechanics and MiningSciences vol 51 pp 24ndash34 2012

[4] Y Chen S Q Ma and Y Yu ldquoStability control of un-derground roadways subjected to stresses caused by extrac-tion of a 10-m-thick coal seam a case studyrdquo Rock Mechanicsand Rock Engineering vol 50 no 9 pp 1ndash10 2017

[5] M Colwell R Frith and C Mark ldquoAnalysis of longwalltailgate serviceability (ALTS) a chain pillar design method-ology for Australian conditionsrdquo in Proceedings of the SecondInternational Workshop on Coal Pillar Mechanics and Designpp 33ndash48 1999

[6] J B Bai and C J Hou ldquoNumerical simulation study onstability of narrow coal pillar of roadway driving along goafrdquoChinese Journal of Rock Mechanics and Engineering vol 23no 20 pp 3475ndash3479 2004

[7] E Jirankova V Petros and J Sancer ldquo4e assessment ofstress in an exploited rock mass based on the disturbance ofthe rigid overlying stratardquo International Journal of RockMechanics and Mining Sciences vol 50 pp 77ndash82 2012

[8] G Zhang Y Tan S Liang and H Jia ldquoNumerical estimationof suitable gob-side filling wall width in a highly gassylongwall mining panelrdquo International Journal of Geo-mechanics vol 18 no 8 article 04018091 2018

[9] G Zhang S Liang Y Tan F X Xie S Chen and H JialdquoNumerical modeling for longwall pillar design a case studyfrom a typical longwall panel in Chinardquo Journal of Geophysicsand Engineering vol 15 no 1 pp 121ndash134 2018

[10] E Esterhuizen C Mark and M M Murphy ldquoNumericalmodel calibration for simulating coal pillars gob and over-burden responserdquo in Proceedings of the Twenty-Ninth In-ternational Conference on Ground Control in Miningpp 46ndash57 Morgantown WV USA July 2010

[11] W F Li J B Bai S Peng X Y Wang and Y Xu ldquoNumericalmodeling for yield pillar design a case studyrdquo RockMechanicsand Rock Engineering vol 48 no 1 pp 305ndash318 2014

10 Advances in Civil Engineering

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

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

stress wave to the nearby retained entry which makes therock around the retained entry under the synergy effect ofabutment stress and dynamic stress 4e results of miningground pressure in the physical model of plane stress canclearly illustrate the mechanical behavior of the rockaround the retained entry with stiff coal pillar under thehard roof [40]

However the physical model can only simulate themechanical behavior of the rock strata behind the workingface during the mining process when it is under the plane-stress condition When there are several hard roofs nearthe mining coal seam this experimental method is a greatoption for predicting the mine ground pressure of the stiffcoal-pillar entry retaining while it is inappropriate forpredicting the deformation behavior of the retained entrywhen the dimension of the entry is just 31mm in widthand 25mm in height In addition when monitoring thedynamic stress induced from the hard roof activationthe monitoring system of high-frequency pressure cell ismore convinced than vibration signals with the acousticemission

5 Conclusions

In order to reveal the mine ground pressure of stiff coal-pillar entry retaining and verify whether this entry can beretained to serve the next panel influenced by the hard roofactivation a 2D physical model with plane-stress conditionswas established to simulate the mechanical behavior of hardroofs behind the working face 4e results of the experi-mental method are concluded as follows

(1) 4e hard roof closed to the gob undergoes bendingdown fracture and caving activation successivelyunless its upper hard roof is strong enough tosupport overlying loads 4e cantilever structurewhich is supported by the stiff coal pillar above thegob faces the potential fracture activation above thestiff coal pillar under the front abutment stress in-duced from the retreating of the next panel

(2) Under the synergistic effects of the side varyingabutment stress and dynamic stress the entrycannot be retained to serve next panel successfullyeven though it is protected with a stiff coal pillarOverlying loads above the worked-out area mainlyhave a loading effect in the stiff coal pillar Besidesthe dynamic stress induced from the hard roofactivation can wave to the underneath retainedentry

(3) 4e experimental method can be used to analyze themechanical behavior of the rock strata during themining process Since the geological and engineeringconditions are different the procedure is still nec-essary for other cases

Data Availability

4e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

4e authors declare that they have no conflicts of interest

Acknowledgments

4is work was supported by the National Natural ScienceFoundation of China (contract nos 51804099 51774111 and51704098) the Key Scientific Research Project Fund ofColleges and Universities of Henan Province (19A440011and 19A130001) the Natural Science Foundation of HenanPolytechnic University (B2018-4 and B2018-65) and theRegional Collaborative Innovation Project of the XinjiangUygur Autonomous Region (2017E0292)

References

[1] P K Mandal R Singh J Maiti A K Singh R Kumar andA Sinha ldquoUnderpinning-based simultaneous extraction ofcontiguous sections of a thick coal seam under weak andlaminated partingrdquo International Journal of Rock Mechanicsand Mining Sciences vol 45 no 1 pp 11ndash28 2008

[2] M Colwell D Hill and R Frith ldquoALTS II a longwallgateroad design methodology for Australian collieriesrdquo inProceedings of the First Australasian Ground Control inMining Conference Sydney NSW Australia August 2003

[3] M Shabanimashcool and C C Li ldquoNumerical modelling oflongwall mining and stability analysis of the gates in a coalminerdquo International Journal of Rock Mechanics and MiningSciences vol 51 pp 24ndash34 2012

[4] Y Chen S Q Ma and Y Yu ldquoStability control of un-derground roadways subjected to stresses caused by extrac-tion of a 10-m-thick coal seam a case studyrdquo Rock Mechanicsand Rock Engineering vol 50 no 9 pp 1ndash10 2017

[5] M Colwell R Frith and C Mark ldquoAnalysis of longwalltailgate serviceability (ALTS) a chain pillar design method-ology for Australian conditionsrdquo in Proceedings of the SecondInternational Workshop on Coal Pillar Mechanics and Designpp 33ndash48 1999

[6] J B Bai and C J Hou ldquoNumerical simulation study onstability of narrow coal pillar of roadway driving along goafrdquoChinese Journal of Rock Mechanics and Engineering vol 23no 20 pp 3475ndash3479 2004

[7] E Jirankova V Petros and J Sancer ldquo4e assessment ofstress in an exploited rock mass based on the disturbance ofthe rigid overlying stratardquo International Journal of RockMechanics and Mining Sciences vol 50 pp 77ndash82 2012

[8] G Zhang Y Tan S Liang and H Jia ldquoNumerical estimationof suitable gob-side filling wall width in a highly gassylongwall mining panelrdquo International Journal of Geo-mechanics vol 18 no 8 article 04018091 2018

[9] G Zhang S Liang Y Tan F X Xie S Chen and H JialdquoNumerical modeling for longwall pillar design a case studyfrom a typical longwall panel in Chinardquo Journal of Geophysicsand Engineering vol 15 no 1 pp 121ndash134 2018

[10] E Esterhuizen C Mark and M M Murphy ldquoNumericalmodel calibration for simulating coal pillars gob and over-burden responserdquo in Proceedings of the Twenty-Ninth In-ternational Conference on Ground Control in Miningpp 46ndash57 Morgantown WV USA July 2010

[11] W F Li J B Bai S Peng X Y Wang and Y Xu ldquoNumericalmodeling for yield pillar design a case studyrdquo RockMechanicsand Rock Engineering vol 48 no 1 pp 305ndash318 2014

10 Advances in Civil Engineering

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

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

[12] M Shabanimashcool and C C Li ldquoA numerical study ofstress changes in barrier pillars and a border area in a longwallcoal minerdquo International Journal of Coal Geology vol 106pp 39ndash47 2013

[13] H Wang Y Jiang Y Zhao J Zhu and S Liu ldquoNumericalinvestigation of the dynamic mechanical state of a coal pillarduring longwall mining panel extractionrdquo Rock Mechanicsand Rock Engineering vol 46 no 5 pp 1211ndash1221 2013

[14] J B Bai W L Shen G L Guo X Y Wang and Y Yu ldquoRoofdeformation failure characteristics and preventive tech-niques of gob-side entry driving heading adjacent to theadvancing working facerdquo Rock Mechanics and Rock Engi-neering vol 48 no 6 pp 2447ndash2458 2015

[15] B Yu Z Zhang T Kuang and J Liu ldquoStress changes anddeformation monitoring of longwall coal pillars located inweak groundrdquo Rock Mechanics and Rock Engineering vol 49no 8 pp 3293ndash3305 2016

[16] H Mohammadi M A E Farsangi H Jalalifar andA R Ahmadi ldquoA geometric computational model for cal-culation of longwall face effect on gate roadwaysrdquo RockMechanics and Rock Engineering vol 49 no 1 pp 303ndash3142016

[17] W L Shen J B Bai W F Li and X Y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[18] W L Shen T Q Xiao M Wang J B Bai and X Y WangldquoNumerical modeling of entry position design a field caserdquoInternational Journal of Mining Science and Technology 2018In press

[19] Z Z Zhang J B Bai Y Chen and S Yan ldquoAn innovativeapproach for gob-side entry retaining in highly gassy fully-mechanized longwall top-coal cavingrdquo International Journalof Rock Mechanics amp Mining Sciences vol 80 pp 1ndash11 2015

[20] L Jiang P Zhang L Chen et al ldquoNumerical approach forgoaf-side entry layout and yield pillar design in fracturedground conditionsrdquo Rock Mechanics and Rock Engineeringvol 50 no 11 pp 3049ndash3071 2017

[21] L Jiang A Sainoki H S Mitri N Ma H Liu and Z HaoldquoInfluence of fracture-induced weakening on coal minegateroad stabilityrdquo International Journal of Rock Mechanics ampMining Sciences vol 88 pp 307ndash317 2016

[22] G C Zhang F L He Y H Lai and H G Jia ldquoGroundstability of an underground gateroad with 1 km burial deptha case study from Xingdong coal mine Chinardquo Journal ofCentral South University vol 25 no 6 pp 1386ndash1398 2018

[23] S H Advani T S Lee and R H Dean ldquoVariational prin-ciples for hydraulic fracturingrdquo Journal of Applied Mechanicsvol 59 no 4 pp 819ndash826 1992

[24] A Van As and R G Jeffrey ldquoHydraulic fracturing as a caveinducement technique at Northparkes minesrdquo in Proceedingsof MASSMIN 2000 Conference pp 165ndash172 Brisbane QLDAustralia October 2000

[25] K Matsui H Shimada and H Z Anzwar ldquoAcceleration ofmassive roof caving in a longwall gob using a hydraulicfracturingrdquo in Proceedings of Fourth International Symposiumon Mining Science and Technology pp 43ndash46 Beijing ChinaAugust 1999

[26] B X Huang Y Wang and S Cao ldquoCavability control byhydraulic fracturing for top coal caving in hard thick coalseamsrdquo International Journal of Rock Mechanics and MiningSciences vol 74 pp 45ndash57 2015

[27] C Lin J Deng Y Liu Q Yang and H Duan ldquoExperimentsimulation of hydraulic fracture in colliery hard roof controlrdquo

Journal of Petroleum Science and Engineering vol 138 no 49pp 265ndash271 2016

[28] C L Han N Zhang B Y Li G Y Si and X G ZhengldquoPressure relief and structure stability mechanism of hard rooffor gob-side entry retainingrdquo Journal of Central South Uni-versity vol 22 no 11 pp 4445ndash4455 2015

[29] B X Huang S Chen and X Zhao ldquoHydraulic fracturingstress transfer methods to control the strong strata behavioursin gob-side gateroads of longwall minesrdquo Arabian Journal ofGeosciences vol 10 no 11 p 236 2017

[30] Q Bai S Tu F Wang and C Zhang ldquoField and numericalinvestigations of gateroad system failure induced by hardroofs in a longwall top coal caving facerdquo International Journalof Coal Geology vol 173 pp 176ndash199 2017

[31] K Xia C Chen X Liu Z Yuan and F Hua ldquoGroundmovement mechanism in tectonic stress metal mines withsteep structure planesrdquo Journal of Central South Universityvol 24 no 9 pp 2092ndash2104 2017

[32] K Xia C Chen H Fu Y Pan and Y Deng ldquoMining-inducedground deformation in tectonic stress metal mines a casestudyrdquo Bulletin of Engineering Geology and the Environmentvol 210 no 3 pp 212ndash230 2016

[33] K Xia C Chen X Liu H Fu Y Pan and Y Deng ldquoMining-induced ground movement in tectonic stress metal minesa case studyrdquo Bulletin of Engineering Geology and the Envi-ronment vol 75 no 3 pp 1089ndash1115 2016

[34] B Ghabraie G Ren X Zhang and J Smith ldquoPhysicalmodelling of subsidence from sequential extraction of par-tially overlapping longwall panels and study of substratamovement characteristicsrdquo International Journal of CoalGeology vol 140 pp 71ndash83 2015

[35] S H Tu Experimental Method andMeasurement Technique ofRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[36] M G Qian P W Shi and J L XuMine Ground Pressure andRock Control China University of Mining and TechnologyPress Xuzhou China 2010

[37] Q Yao Z Jian Y Li Y Tan and Z Jiang ldquoDistribution ofside abutment stress in roadway subjected to dynamicpressure and its engineering applicationrdquo Shock and Vibra-tion vol 2015 Article ID 929836 11 pages 2015

[38] Y Hamiel V Lyakhovsky and Y Ben-Zion ldquo4e elasticstrain energy of damaged solids with applications to non-linear deformation of crystalline rocksrdquo Pure and AppliedGeophysics vol 168 no 12 pp 2199ndash2210 2011

[39] W L Shen J B Bai X Y Wang and Y Yu ldquoResponse andcontrol technology for entry loaded by mining abutmentstress of a thick hard roofrdquo International Journal of RockMechanics and Mining Sciences vol 90 pp 26ndash34 2016

[40] P Wang L Jiang J Jiang P Zheng and W Li ldquoStratabehaviors and rock-burst-inducing mechanism under thecoupling effect of a hard thick stratum and a normal faultrdquoInternational Journal of Geomechanics vol 18 no 2 article04017135 2018

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

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