AnalysisofOverburdenStructureandPressure-ReliefEffectof...

Research ArticleAnalysis of Overburden Structure and Pressure-Relief Effect ofHard Roof Blasting and Cutting

Hao Liu1 Jin Dai2 Jinquan Jiang12 Pu Wang 12 and Jiqiang Yang3

1State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province andthe Ministry of Science and Technology Shandong University of Science and Technology Qingdao 266590 China2Department of Resources and Civil Engineering Shandong University of Science and Technology Tairsquoan 271019 China3China Coal Tianjin Design Engineering Co Ltd Tianjin 300120 China

Correspondence should be addressed to Pu Wang 15854848872163com

Received 2 March 2019 Revised 8 August 2019 Accepted 26 August 2019 Published 16 September 2019

Academic Editor Zahid Hossain

Copyright copy 2019Hao Liu et al-is is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

When studying the pressure-relief effect of hard roof blasting and cutting the roof-cutting position and angle obviously affect thestability of the rock surrounding the gob-side entry (GSE) In this paper control of the large deformation of rock surrounding theGSE is evaluated on the basis of the overlying structure and pressure-relief principle caused by roof cutting Moreover amechanics model of a three-hinged arch structure (THAS) and a universal distinct element code (UDEC) numerical model withregard to the overlying rock movement were established to study the relationship among the rotation angle of key blocks in theTHAS the width of the roadway and the wall force beside it and the optimal cutting position and cutting angle to reveal thepressure-relief effect of roof blasting and cutting and its influence on the support stability of the roadway-e results show that theoverlying rock can form a stable THAS after roof blasting and cutting and that the wall stress and the coal-wall displacement aresmall which indicates that roof blasting and cutting results in obvious pressure relief -e wall force increases with an increase inthe rotation angle of the key block and decreases with an increase in the roadway width Moreover the optimal roof-cuttingposition (5m) and angle (15deg) are obtained with the specific mining conditions Finally on-site monitoring of the anchor-cableforce and support force in panel 5312 of the Jining no 3 coal mine is used to verify the pressure-relief effect after roof blasting andcutting -e study results can provide a theoretical basis for reasonable technical means and optimization of supporting pa-rameters in field observation and have important application value for roof cutting and pressure relief for GSE retaining(GSER) technology

1 Introduction

Based on green scientific and efficient mining of coal re-sources gob-side entry retaining (GSER) technology has beenwidely applied to underground coal mines -is technologyessentially realizes continuous mining without a coal pillarreduces the roadway excavation rate eases the difference be-tweenmining and excavation and optimizes themining layoutHowever this technology is restricted by several shortcomingsin its development and application such as the diversity of roofposition difficulty in controlling large deformation of thesurrounding rock andmismatch between the characteristics ofthe wall support and the surrounding rock [1ndash4]

For that reason in-depth studies on the key technologies ofGSER such as the surrounding rock activity wall support androadway support have been conducted [5ndash9] Because GSER isapplied along the edge of the goaf after mining of the workingface the stability of the surrounding rock might depend on themechanical response of roof failure -e sliding-rotating (S-R)stability based on the Voussoir beam theory was put forward byQian et al [10 11] regarding the key block and the mechanicscriterion of slipping or rotary instability for the key block wasobtained -e lateral roof of the roadway at the goaf side mightbreak at the elastic-plastic junction thus the fracture position ofkey strata was obtained according to the limit equilibriumtheory [12ndash16] Guo and Zhao [17] determined that the fracture

HindawiAdvances in Civil EngineeringVolume 2019 Article ID 1354652 14 pageshttpsdoiorg10115520191354652

location of the lower roof of the retaining roadway plays aguiding role for the entire roof of the gob-side entry (GSE)

When a hard thick main roof occurs over a coal seamwhere no immediate roof is present or the immediate roof isthinner the wall beside the roadway may have difficulty insupporting the hard roof -erefore it is necessary to presplitthe hard roof and to change the main roof structure thusresulting in effective pressure alleviation of the GSE [18ndash22]At present commonly used methods for roof presplitting areblasting presplitting and hydraulic fracturing [23 24] whichcan effectively cut off the overhanging roof above theretaining roadway and result in roof caving However whenusing hydraulic fracturing for a hard roof the mechanicalproperties of the roof decrease through the interaction of rockand water [25 26]-erefore blasting presplitting is generallyused for a hard roof -e traditional use of roof blasting andpressure relief is to advance the presplitting blasting on theroof which can speed up themovement and reduce the lengthof the cantilever block thus reducing the pressure and thedeformation of the surrounding rock In addition a verticalblastingmodel of bedrock was established through optimizingthe charge structure of borehole and then the influence ofblasting-hole diameter on the blasting effect is determined byusing a numerical simulation and field test [27 28] Cu-mulative blasting technology with directional presplittingunder composite-roof condition was adopted to effectivelycontrol the damage of roof and maintain the integrity of thecollapsed roof [29] A dynamic load numerical model whichregards artificial blasting as the earthquake source wasestablished in order to analyze the failure and deformation ofsurrounding rocks [30] However these previous studies donot consider the importance of the structure formed by roofcollapse and movement

Hence it is particularly important to select the bestcutting position (hole position) and angle (hole angle) whenpresplit blasting the roof to achieve better pressure-reliefeffects In this paper to control the large deformation of rocksurrounding the GSE the overlying structure and pressure-relief principle caused by roof cutting was first analyzed ATHAS mechanics model and a UDEC numerical model withregard to the overlying rock movement were established tostudy the relationship among the rotation angle of key blocksin THAS the width of the roadway and the wall force besideit and the optimal cutting position and cutting angle to revealthe pressure-relief effect of roof blasting and cutting and itsinfluence on the support stability of the roadway -e studyresults can provide a theoretical basis for reasonable technicalmeans and optimized supporting parameters in field obser-vation Moreover they have important application value forroof cutting and pressure relief using GSER technology

2 Analysis of Pressure Relief Caused by RoofBlasting and Cutting

21 Overburden Structure and Pressure-Relief PrincipleCaused by Roof Cutting When a hard thick main roofoccurs directly above a coal seam it is easily suspended at alarge scale owing to its high stiffness and strength whichresults in highly concentrated stress in the surrounding rock

of the roadway [31ndash34] Hence if the roof is presplit byblasting in a certain range outside the GSE the length of thecantilever block can be reduced and the caved rock block canbe squeezed and bitten with the noncaved block to form astable articulated structure thus reducing the pressure andalleviating the deformation of the rock surrounding the GSE

-e overburden structure after roof blasting was appliedis shown in Figure 1 As shown in Figure 1(a) the B2 block isrotated and its right side touches the floor first -e blockstill intersects with and presses against the B1 block to form abeam structure owing to the effect horizontal force and thefrictional resistance of joint-cutting -is results in loadexertion on the roadway and shows a poor pressure-reliefeffect In Figure 1(b) the key B2 block is completely cutdown after roof cutting and has lost mechanical trans-mission with the B1 block which has a short or even nocantilever However the position of roof cutting should notbe too close to the roadway in the field mainly because theblasting vibration caused by roof cutting will cause largedeformation of the rock surrounding the roadway InFigure 1(c) the key B2 block has subsided after roof cuttingand the B1 block is suspended for a certain length -en theB1 block was rotated and squeezed with the B2 block withface mining-is resulted in the formation of a three-hingedarch overlying structure transferred from the cantileverbeam structure and thus reduced the pressure of the wall andsurrounding rock

22 Determining Parameters of Roof Cutting According tothe aforementioned analysis the overlying structure afterroof cutting is very important for the stability of the sur-rounding rock in GSER technology -e basic parametersdetermining the overlying structure are the position and theangle of roof cutting

2210eoretical Analysis of Roof-Cutting Angle According tothe Voussoir beam theory [10] in order to ensure theslipping of block B2 the shear force must be greater than thefriction force between the two blocks as

R

Tge tan(φ minus β) (1)

where R is the shear force with the block failure N Tis horizontal force N and β is the angle of the roof cutting

-e possibility of slipping instability of the structureincreases with an increase in the cutting angle However thecutting angle should not be too large which may cause thedrill-hole depth to increase thus increasing the difficulty ofconstruction

222 0eoretical Analysis of Roof-Cutting Position If the B2block slips and loses stability after roof cutting the relationshipamong the rotation angle cutting angle and cutting position isdescribed by drawing a method according to the geometricrelationship of the blocks as shown in Figure 2 -e B1 blockrotated more easily and sank with a decrease in the cuttingangle then it made contact with the B2 block to form a THAS

2 Advances in Civil Engineering

According to the above analysis the THAS easily formswith a large cutting position or small cutting angle Howevera longer cantilever relates to high support stress of theroadway with a larger cutting position thus the B2 block mayslip more easily with a large cutting angle according toequation (1) Hence it is necessary to choose an appropriatecutting angle and cutting position to form a THAS

3 Mechanical and Parameter Analysis ofOverburden Structure Caused byRoof Cutting

31 Mechanical Model and Numerical Example Analysis ofOverburden Structure In order to better understand thepressure-relief effect of THAS after roof cutting the

Hard roof

Block A

Block B1Block B2 Block C

Presplit

Roadway wallIntegrated coal Goaf

L1 L2

Coal

Floor

θ1θ2

(a)

Hard roof

Block A

Block B1

Block CBlock B2

Presplit


L1 L2

Coal

Floor

θ1

(b)

Hard roof

Block A

Block B1

Block CBlock B2

Presplit


L1 L2

Coal

Floor

θ1

(c)

Figure 1 Roof structure of GSE affected by roof cutting

Advances in Civil Engineering 3

short-arm beam structure was set as the matched group themechanical model of the key block was established and theengineering example was analyzed

Figure 3 shows the force condition of the key strata withthe THAS formation According to the S-R stability theoryequation (2) is obtained

1113944 MA 0e

2T +

12

qL12

minus fL1

minus P a + b +c

21113874 1113875 minus T(h minus m) 0

(2)

where T is the horizontal force and T qL122(h minus

L1 sin θ1) f is the friction force between two adjacent blocksand f T tanφ tan φ is the friction coefficient P is the wallforce N q is the uniform load q cihi ci and hi are thedensity and the height of the main roof and its overlyingstrata respectively and e 12(h minus L1 sin θ1) Henceequation (3) can be expressed by the above parameters

P (q tanφ) 2 h minus L1 sin θ1( 1113857( 1113857( 1113857L1

3 minus q m minus 3L1 sin θ1( 1113857( 1113857 8 h minus L1 sin θ1( 1113857( 1113857( 1113857L12

a + b +(c2) (3)

Figure 4 shows the force condition of the key strata withthe cantilever beam structure -us the following equationsare obtained

1113944 MA 012

qL12

minus P a + b +c

21113874 1113875 0 (4)

P qL1

2

2a + 2b + c (5)

Hence when the cantilever beam structure and THAS areformed the wall force increases with an increase in L1

Among them the wall force P of the cantilever beamstructure is minimal with L1 a+ b+ c when a THAS formsL1 needs to satisfy the geometric relations in Figure 2

In order to study the problem intuitively panel 5312 ofthe Jining No 3 coal mine was used as the miningbackground -e depth of panel 5312 is 581m the mining

height is 3m the coal seam dip is 3ndash6deg and the length and thestrike length are 150m and 626m respectively-e excavationsize of the GSE is 45mtimes 3m and the width of the wall is27m Moreover the roof is composed mainly of interbeddedsandstone and mudstone -e physical and mechanical pa-rameters of the coal and the roof are listed in Table 1

-e length L of the B block can be obtained as [8]

L 2u

17

10z

u1113874 1113875

2+ 102

1113971

minus 10z

u⎛⎝ ⎞⎠ (6)

where u is the length of working face m z is the periodicweighting distance obtained by field observation or calcu-lated by z 2h

(RTq)

1113968 and RT is the tensile strength MPa

Considering the effect of the elastic foundation thehorizontal distance between the break line of the roof andthe roadway can be obtained as [1]

Block B1Block B2

L1

β

θ1

(a)

5 10 15 20 25

2

3

4

5

6

7

8

β (deg

)

L1 (m)

β = 5degβ = 10degβ = 15deg

β = 20degβ = 25deg

(b)

Figure 2 Relationship among rotation angle cutting angle and cutting position (a) Geometric relationship between blocks(b) relationship between the rotation angle and cutting position


a arctan rβQ0 + 2β2M0s1113872 1113873 r2M0 + βrQ0( 11138571113960 1113961

β (7)

where E is the elastic modulus of main roof GPa k is thefoundation coefficient and k Eprimem Eprime is the elastic mod-ulus of the coal seam and Eprime E(1 minus v2) I is the bendingmodulus of main roof and I h312M0 is bending momentabove the coal wall and Q0 is the shear force above the coalwall In addition r

(kEprimeI)

1113968 s TEprimeI β (r2)12

Q0 qL and M0 qL22According to the geological conditions of panel 5312 the

parameters z 317m L 306m and a 37m can becalculated by equations (6) and (7) According to previousresearch [9] the rotation angle of the main roof was set at 4deghence the relationship among the roof cutting the wall forceof the cantilever beam structure and THAS is shown inFigure 5

As can be seen from Figure 5 whether the roof is in acantilever beam or a THAS reducing the length of the blockby cutting the roof can play amore obvious pressure-relief effectWhen the cantilever beam structure is formed after roof cuttingthe minimum roof-cutting position is L1 a+b+ c 87m atthis moment the roof cantilever length is 0m and the wallforce is 3633 kN While when the wall force is 3633 kN theTHAS is formed after roof cutting and the cutting position is13m and the roof cantilever length is 43m According to theanalysis of Section 22 the longer the cantilever length is theeasier the THAS will be formed Considering the field en-gineering the cutting position should not be too close to theroadway because the blasting impact and the roof subsidenceafter presplit blasting will cause serious deformation of sur-rounding rocks which is not conducive to the stability of theroadway Hence it can be concluded that the THAS is moreconducive to the stability of the rock surrounding the GSE in

Table 1 Physical and mechanical parameters of coal and roof

Lithology -ickness(m)

Density(kNmiddotmminus 3)

Modulus of elasticity(GPa)

Poissonrsquosratio

Tensile strength(MPa)

Internal frictionangle (deg) Note

Coal seam 3 135 22 043 041 148Siltstone 907 241 22 027 42 32 Main roofSand shaleinterbed 893 257 156 029 37 31 Compensated

load

h

m

a b c

C

B

A

q

TT

P

05eBlock B1

Block B2

L1

θ1

Figure 3 Mechanical model of the THAS

Block B1

q

P

a b c

L1

A

Figure 4 Mechanical model of the cantilever beam structure


panel 5312 and that the best position of roof presplitting isabout 5m outside the roadway

32 Analysis of Key Parameters of GSER According toequation (5) many factors such as the coal-seam thicknessoverlying load key block movement and roadway widthaffect the wall force In this study the objective geologicalfactors (eg coal seam thickness and overlying load) werenot considered Instead we studied the relationship of thekey-block rotation angle the roadway width (wall width)and the wall force

Figure 6 shows the variation curve of the relationshipamong the rotation angle of the key block roadway width(wall width) and the wall force It can be concluded that thewall force increases with an increase in the rotation angle ofthe key block whereas it decreases with an increase in theroadway width Moreover the rotation angle of θ1 decreaseswith increases in the stiffness of the wall and in the coal seambecause it is obviously affected by these parameters and thestress in the rock surrounding the roadway increases with anincrease in θ1 Hence bolt support at the coal side can beadopted or high-strength wall-filling material can be usedthus increasing the bearing capacity and effectively im-proving the stability of the rock surrounding the roadway Inaddition a decrease in the wall force will inevitably lead to anincrease in the coal force of the roadway according to themechanical balance for the B1 block which leads to largedeformation and is not conducive to controlling the rocksurrounding the roadway Hence it is necessary to design areasonable roadway width for GSE stability

4 Analysis of Numerical Simulation

41 Establishment of the Numerical Model In order tofurther reveal the influence of roof presplitting and cuttingtechnology on the stress and deformation of the surrounding

rock for GSER UDEC numerical simulation was used tostudy the pressure-relief effects of the roof cutting angle andcutting position As a result the best roof-cutting angle andcutting position were obtained Hence a total of 32 differentcombination schemes were designed by setting differentcutting angles such as 0deg 10deg 15deg and 25deg and differentcutting positions such as 1m 3m 5m 7m 9m 11m 13mand 15m-e sizes of the simulationmodel and the roadwaywere 200m (length)times 81m (height) and 45m (width)times 3m(height) respectively and the wall width was 27mMoreover the boundary conditions of the bottom and bothsides of this model were full-displacement constraints andhorizontal-displacement constraints respectively and themodel top applied 125MPa vertical stress to compensate forthe failed simulation strata -e MohrndashCoulomb model wasadopted for the coal and rockmass and the strain-hardeningmodel was adopted for the wall An overview of the sim-ulation model and its parameters are shown in Figure 7

42 Analysis of the Angle Effect of Roof Cutting -e simu-lation results of the 32 aforementioned schemes revealedthat the roof structure changes similarly with the cutting-angle variation at different cutting positions Hence thecutting position of 5m was chosen and the structure var-iations with different cutting angles as shown in Figure 8were analyzed

-e different cutting angles had different effects on themovement of key blocks after roof cutting It was easier forthe B2 block to be fully cut down to the horizontal state withan increase in the cutting angle When the cutting angle wasless than 15deg as shown in Figures 8(a) and 8(b) the influenceof roof cutting on the overburden structure was small themovement of overburden is slight and the pressure-reliefeffect was not obvious When the cutting angle was greaterthan 15deg (Figure 8(d)) the B2 block was completely cut downand was relatively isolated therefore it could not makecontact with the cantilever of the B1 block to form a stableTHAS However when the cutting angle was 15deg as shownin Figure 8(c) the B2 block was cut down and the B1 blockwas squeezed and occluded to form a THAS which can havean obvious pressure-relief effect Hence the optimal angle ofroof cutting for pressure relief is 15deg for these simulationconditions

43 Analysis of the Position Effect of Roof CuttingAccordingly in order to study the position effect of roofcutting for pressure relief the cutting angle of 15deg waschosen and the structure variations with different cuttingpositions as shown in Figure 9 are analyzed

When the cutting angle was 15deg the blocks with differentcutting positions can be squeezed and bitten however thepressure-relief effect for the main roof is different When thecantilever length is less than 5m (Figures 9(a) and 9(b)) thekey block can form an articulated structure but the B2 blockabove the goaf cannot fully move which affects the stabilityof the articulated structure and the stress of the surroundingrock for GSE When the cantilever length is 5m as shown inFigure 9(c) the B2 block can be sufficiently cut down to form

0 2 4 6 8 10 12 148 10 12 14

16 18 20 22

21 times 104

18 times 104

15 times 104

12 times 104

90 times 103

60 times 103

30 times 103

00

Supp

ort r

esist

ance

(N)

Coal Roadway Wall GobL1 (m)

Minimum cutting location

THASCantilever

Figure 5 Relationship between the roof cutting and the wall forceof different overburden structure


a stable three-hinged arch structure with the B1 block In thiscase the pressure-relief effect for the surrounding rock isremarkable and the deformation of the coal side can beeffectively controlled When the cantilever length is greaterthan 5m (Figure 9(d)) the key B2 block can still be cut downsufficiently although the increase in cantilever length willload more pressure to the rock surrounding the roadwayHence the optimal position of roof cutting for pressure reliefis a cantilever length of 5m under these simulation con-ditions -is result is essentially consistent with the theo-retical analysis results of 43m which indicates that thenumerical simulation design is more reasonable

44 Effect of THAS on Rock Surrounding the GSE -e THASof the main roof is beneficial to the stability of rock sur-rounding the GSE however THAS formation is closelyrelated to the cutting angle and the cutting position-roughthe study and analysis of 32 schemes it was found that thecritical values for THAS formation are a cutting angle of 10degcutting position of 13m angle of 15deg and position of 5m as

shown in Figure 10 -e displacement variations of the coalside of the GSE before and after the THAS formation aredepicted in Figure 11

As shown in Figures 10(a) 10(c) and 11 the THAS wasnot formed after roof cutting and the stability of the mainroof above the roadway was poor causing serious de-formation to the coal side and floor heaving of the GSEwhich seriously affect the normal use of the roadwayHowever Figures 10(b) 10(d) and 11 show THAS for-mation in which the roadway deformation at the coal side isrelatively uniform

-e wall beside the roadway can provide effective sup-port for the roadway and can share part of the load for thesolid coal body of the roadway Hence the stress concen-tration in the wall is obviously reduced after the THASformation As shown in Figures 10(c) and 10(d) the verticalstress in the wall was 253MPa before the THAS formationbut fell to 189MPa with a decrease rate of 25 after thestructure formed Hence to alleviate the pressure andcontrol the deformation of the surrounding rock it is of

Roadway position3m times 45m

Thickness

15m10m

16m

9m

9m3m

9m

10m

Lithology

LimestoneMudstoneMediumgrained

sandstoneSandy

mudstoneSiltstone

CoalFine

sandstone

Andymudstone

Figure 7 Numerical model

0 1 2 3 4 5 6 7

3680

3660

3640

3620

3600

3580

3560

Supp

ort r

esist

ance

(N)

Rotation angle (deg)

(a)

4800

4400

4000

3600

3200

280030 35 40 45 50 55 60 65

Supp

ort r

esist

ance

(kN

)

Roadway width (m)

(b)

Figure 6 Relationship among (a) rotation angle of the key block and the wall force and (b) roadway width and wall force


(a) (b)

(c) (d)

Figure 9 Variations of roof structure with different cutting positions (a) 1m (b) 3m (c) 5m and (d) 7m

(a) (b)

(c)

B1B2

Not contact

(d)

Figure 8 Variations of the roof structure with different cutting angles (a) 0deg (b) 10deg (c) 15deg and (d) 25deg


great significance to reasonably choose the cutting angle andcutting position

-e vertical stress of the wall in Figure 10(b) is obvi-ously less than that of the wall in Figure 10(d) and thedeformation of the former is less than that of the latter asshown in Figure 11 Hence the optimal scheme of roofcutting was determined to be a 15deg cutting angle and a 5mcutting position Moreover referring to the previousstudies [35ndash38] it can be found that the simulation resultsfrom this paper are basically consistent with the results

from those which proves the scientificity of the simulationresults and the rationality of the simulation methods to acertain extent

45 Comparative Analysis of Pressure-Relief Effect betweenRoof Cutting and Non-Roof-Cutting According to the afore-mentioned optimal scheme of roof cutting (cutting angle of15deg and cutting position of 5m) the vertical stress distributionand its variations of roof cutting and non-roof-cutting were

Backfill wall

Roof

CoalFloor

ndash4500E + 07ndash4000E + 07ndash3500E + 07ndash3000E + 07ndash2500E + 07ndash2000E + 07ndash1500E + 07ndash1000E + 07ndash5000E + 06

0000E + 00

(a)


0000E + 00

(b)


0000E + 00

(c)


0000E + 00

(d)

Figure 10 Stress distribution of surrounding rock before and after the THAS formation (a) Cutting angle 10deg and position 11m (b) cuttingangle 10deg and position 13m (c) cutting angle 15deg and position 3m and (d) cutting angle 15deg and position 5m

08

07

06

05

04

03

02

01

0000 05 10 15 20 25 30

Gob-side entry height (m)

Disp

lace

men

t (m

)

Cutting angle 10deg andposition 11mCutting angle 10deg andposition 13m


Figure 11 Displacement variation of coal side of GSER before and after the THAS formation


studied by setting up two monitoring lines 05m above theroadway as shown in Figure 12

Because of the roadway excavation and face mining astress concentration zone occurs in the solid coal and in thewall of the roadway with and without roof cutting Howeverthe roadway is in the stress relaxation zone between the twozones of stress concentration -e vertical stress of the wallwithout roof cutting was 179MPa whereas that of the wallwith roof cutting was 119MPa showing a 33 decreaseMoreover compared with that without roof cutting thestress concentration zone moved forward after roof cuttingand the influence range decreased Hence the pressure-reliefeffect with roof cutting is obvious

Figure 13 shows the displacement variations of the rocksurrounding of the roadway with and without roof cuttingBefore roof cutting the stress concentration was large in thewall and in the solid side of the roadway owing to the highstrength and stiffness of the main roof resulting in obviousdeformation of the roadway After roof cutting the mainroof inside the cutting line rotated and sank In addition aTHAS formed with the block outside the cutting line whichdecreased the stress of the surrounding rock and controlledthe deformation of the roadway Among factors the pres-sure-relief effect of the roadway at the solid coal side was themost remarkable

5 Field Observations

Based on the geological conditions of panel 5312 in theJining No 3 coal mine the optimal cutting position andangle of presplitting blasting for pressure relief were ob-tained In order to further explain the effects of roof cuttingand pressure relief this section discusses on-site monitoringperformed during the mining process of panel 5312 andanalyzes the force of the roof anchor cable and the variationof the support stress

51 Force Monitoring of Roof Anchor Cable According tothe objectives of this study a total of seven anchor-cableforce sensors marked as A1ndashA7 were installed in thetarget roadway-e distances between the sensors and theopen-off cut were 30 m 150 m 215m 230m 350 m450 m and 650m for A1 to A7 respectively and theanchor-cable force was monitored by using a remoteonline-monitoring system Figure 14 describes the forcevariations of A2 A4 and A7 anchor cables with typicalmining conditions

Distance of gob-side entry (m)

ndash30 ndash25 ndash20 ndash15 ndash10 ndash5 0 5 10 15 20 25 30

Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall

Entity coal Gob side

No pressure reliefAfter pressure relief

Figure 12 Stress distribution and its variations of roof cutting and non-roof-cutting

0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)

Gob-side entry width (m)

0 1 2 3 4 5Gob-side entry height (m)

Y-disp of roof withnon-roof-cutting

X-disp of wall withnon-roof-cutting

X-disp of coal side withnon-roof-cutting

Y-disp of roof withroof-cutting

X-disp of wall withroof-cutting

X-disp of coal side withroof-cutting

Backfill wall

Figure 13 Displacement variations of surrounding rocks of theroadway with roof cutting or non-roof-cutting


-e force variations of the roof anchor cables in the threemonitoring positions were similar and the influence rangeof mining dynamic pressure was essentially stable at 30ndash35m -e force of the anchor cable began to increase about10m between the monitoring point and the working face-e growth rate gradually intensified When the distancebetween the face and the point was about 8m the force ofanchor cable reached its peak value and then rapidly de-creased When the working face pushed through themonitoring point for 30m the force essentially stabilized at150 kN indicating that the roof of the retaining roadway hadbeen cut down along the presplitting face to successfullyrelieve the pressure

52 Stress Monitoring of Supports During the mining pro-cess of panel 5312 a total of 100 hydraulic supports of typeZY7200-18534 were selected -e rated working resistanceof the support was 7200 kN (40MPa) and the maximumsupport height was 3400mm -e stress monitoring pointsof the supports were arranged as shown in Figure 15 Astress-monitoring point was arranged in increments of eightsupports ie on support Nos 3 11 19 27 35 43 51 59 6775 83 91 and 99 for on-line real-time monitoring of thestress data

According to the aforementioned monitoring schemethe stope can be divided into three areas the roof-cutting-affected zone the unaffected area in the middle and the zone

150m

51 913

Roof cuttingaffected zone

Gob-side entry

Non-roof-cuttingaffected zone

Middle unaffectedzone

Gob

Figure 15 Monitoring points of support stress

350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60

Distance behind the coal face (m)

Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7

Figure 14 Monitoring curve of anchor-cable force


not affected by roof cutting -ree hydraulic supports Nos3 51 and 91 were selected to monitor and analyze the rockpressure Among them support No 3 was located in thezone not affected by roof cutting No 51 was located in themiddle unaffected zone and No 91 was located in the roof-cutting-affected zone

Figure 16 and Table 2 show statistical curves of thesupport load and the weighting step -e first weighting andperiodic weighting of support No 3 in the zone not affectedby roof cutting were 44m and 26m respectively those of No91 in the zone affected by roof cutting were 50m and 31mrespectively -e two parameters of the latter are obviouslylarger than those of the former indicating that a stable THASformed between the collapsed and noncollapsed roof afterroof cutting and that the rotary deformation of the non-collapsed roof was small -is prevented the main roof fromeasily breaking that is the breaking span of the main roofincreased -e decrease in support resistance indicates that acaving roof provides a certain degree of support for a non-caving roof and that the pressure of the noncaving roof on therock surrounding the GSE decreases correspondingly

6 Conclusions

Regarding the pressure-relief effects of hard roof blastingand cutting the factors selected for the roof cutting positionand its angle obviously affects the surrounding rock stabilityof the GSE In this study which focused on controlling thelarge deformation of this rock the following results wereobtained

(1) Based on the analysis of the overlying structure andpressure-relief principle caused by roof cutting amechanical model of a THAS is established It wasdetermined that the overlying rock can form a stableTHAS after roof blasting and cutting In addition thewall stress and the coal-wall displacement were smallwhich indicates that roof blasting and cutting hasobvious effects of pressure relief

(2) Taking panel 5312 of the Jining No 3 coal mine asthe engineering background the relationshipamong the rotation angle of the key block the widthof roadway and the wall force beside the roadwaywas studied -e wall force was found to increasewith an increase in the rotation angle of the keyblock but decreased with an increase in the roadwaywidth

(3) -e effects of roof-cutting position and angle werestudied with optimal results found to be 5m and 15degrespectively Finally on-site monitoring of the an-chor-cable force and the support force in panel 5312of the Jining No 3 coal mine was used to verify thepressure relief effect after roof blasting and cutting

-ese study results can provide a theoretical basis forreasonable technical means and optimization of supportingparameters in field observation Moreover they have im-portant application value for roof cutting and pressure reliefin GSER technology

Data Availability

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

Conflicts of Interest

-e authors declare that there are no conflicts of interest

0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)

Face advance distance (m)

3 support51 support91 support

Average value 259MPa

Average value 173MPa Average value 212MPa

Figure 16 Variation curve of support load

Table 2 Statistics of weighting and support stress

No First weighting (m) Periodic weighting (m) Support stress(MPa)

3 50 31 17351 40 19 25991 44 26 212


Acknowledgments

-is study was funded by the National Natural ScienceFoundation of China (nos 51574155 and 51804182) Scienceand Technology Development Plan of Tairsquoan (no2018GX0045) Shandong Provincial Natural Science Foun-dation (no ZR2019BEE065) Scientific Research Foundationof Shandong University of Science and Technology forRecruited Talents (no 2015RCJJ057) and Shandong Pro-vincial Key RampD Plan (Public Welfare Special Program) ofChina (no 2017GGX20125)

References

[1] Q Wang M He J Yang H Gao B Jiang and H Yu ldquoStudyof a no-pillar mining technique with automatically formedgob-side entry retaining for longwall mining in coal minesrdquoInternational Journal of Rock Mechanics and Mining Sciencesvol 110 no 1 pp 1ndash8 2018

[2] L S Jiang P Kong J M Shu and K G Fan ldquoNumericalanalysis of support designs based on a case study of longwallentryrdquo Rock Mechanics and Rock Engineering pp 1ndash12 2019

[3] P Wang L S Jiang X Y Li G P Qin and E Y WangldquoPhysical simulation of mining effect caused by A fault tec-tonicrdquo Arabian Journal of Geosciences vol 11 no 23 p 7412018

[4] P Wang L S Jiang X Y Li P Q Zheng and G P QinldquoEffects of strength weakening and interface slipping on rockmass with different dip angle structure planesrdquo Acta Geo-dynamica et Geomaterialia vol 15 no 4 pp 329ndash338 2018

[5] S Yan T Liu J Bai andWWu ldquoKey parameters of gob-sideentry retaining in a gassy and thin coal seam with hard roofrdquoProcesses vol 6 no 5 p 51 2018

[6] J G Ning XS Liu J Tan QH Gu Y L Tan and J WangldquoControl mechanisms and design for a ldquocoal-backfill-ganguerdquosupport system for coal mine gob-side entry retainingrdquo In-ternational Journal of Oil Gas and Coal Technology vol 18no 3-4 pp 444ndash466 2018

[7] D W Yang Z G Ma and F Z Qi ldquoOptimization study onroof break direction of gob-side entry retaining by roof breakand filling in thick-layer soft rock layerrdquo Geomechanics andEngineering vol 13 no 2 pp 195ndash215 2017

[8] X Li M Ju Q Yao J Zhou and Z Chong ldquoNumericalinvestigation of the effect of the location of critical rock blockfracture on crack evolution in a gob-side filling wallrdquo RockMechanics and Rock Engineering vol 49 no 3 pp 1041ndash10582016

[9] G C Zhang Y L Tan S J Liang and H-G Jia ldquoNumericalestimation of suitable gob-side filling wall width in a highlygassy longwall mining panelrdquo International Journal of Geo-mechanics vol 2018 no 8 Article ID 04018091 2018

[10] M G Qian Rock Stratum Control and the Scientific Collectionof Coal China University of Mining and Technology PressXuzhou China 2011

[11] Z Zhang J XuW Zhu and Z Shan ldquoSimulation research onthe influence of eroded primary key strata on dynamic stratapressure of shallow coal seams in gully terrainrdquo InternationalJournal of Mining Science and Technology vol 22 no 1pp 51ndash55 2012

[12] X Wang J Xu W Zhu and Y Li ldquoRoof pre-blasting toprevent support crushing and water inrush accidentsrdquo In-ternational Journal of Mining Science and Technology vol 22no 3 pp 379ndash384 2012

[13] W X Zheng Q W Bu and Y Q Hu ldquoPlastic failure analysisof roadway floor surrounding rocks based on unified strengththeoryrdquo Advances in Civil Engineering vol 2018 Article ID7475698 10 pages 2018

[14] Y Pan Z Q Wang and A W Li ldquoAnalysis of hard roofdeflection bending moment and energy change during thefirst fracturerdquo Chinese Journal of Rock Mechanics and Engi-neering vol 31 no 1 pp 32ndash41 2012

[15] Z Li J Xu J Ju W Zhu and J Xu ldquo-e effects of therotational speed of voussoir beam structures formed by keystrata on the ground pressure of stopesrdquo International Journalof Rock Mechanics and Mining Sciences vol 108 pp 67ndash792018

[16] M G Qian X X Miao and J L Xu0eory of Key Stratum inGround Control China University of Mining and TechnologyPress Beijing China 2010

[17] J W Guo and J W Zhao ldquo-e study on the breaking rule andcontrol mechanism of gob-side entry retaining of the lowerroofrdquo Journal of Mining amp Safety Engineering vol 29 no 6pp 802ndash807 2012

[18] Z Zhang N Zhang H Shimada T Sasaoka and S WahyudildquoOptimization of hard roof structure over retained goaf-sidegateroad by pre-split blasting technologyrdquo InternationalJournal of Rock Mechanics and Mining Sciences vol 100pp 330ndash337 2017

[19] J Ning J Wang L Jiang N Jiang X Liu and J JiangldquoFracture analysis of double-layer hard and thick roof and thecontrolling effect on strata behavior a case studyrdquo Engi-neering Failure Analysis vol 81 pp 117ndash134 2017

[20] M C He S Y Chen Z B Guo J Yang and Y B GaoldquoControl of surrounding rock structure for gob-side entryretaining by cutting roof to release pressure and its engi-neering applicationrdquo Journal of China University of Mining ampTechnology vol 46 no 5 pp 959ndash969 2017

[21] L H He J G Wang and J Q Xiao ldquoPre-splitting blastingvibration reduction effect research on weak rock massrdquo In-ternational Journal of Rock Mechanics amp Mining Sciencesvol 6 pp 338ndash343 2013

[22] P K Singh M P Roy and R K Paswan ldquoControlled blastingfor long term stability of pit-wallsrdquo International Journal ofRock Mechanics and Mining Sciences vol 70 pp 388ndash3992014

[23] F Wang S Tu Y Yuan Y Feng F Chen and H Tu ldquoDeep-hole pre-split blasting mechanism and its application forcontrolled roof caving in shallow depth seamsrdquo InternationalJournal of Rock Mechanics and Mining Sciences vol 64pp 112ndash121 2013

[24] B Huang Q Cheng X Zhao and C Kang ldquoHydraulicfracturing of hard top coal and roof for controlling gas duringthe initial mining stages in longwall top coal caving a casestudyrdquo Journal of Geophysics and Engineering vol 15 no 6pp 2492ndash2506 2018

[25] D Zhao Z C Feng and Y S Zhao Effects and Influencesof Water Injection on Coalbed Exploitation in MiningEngineering pp 731ndash735 Press-Taylor amp Francis GroupBoca Raton FL USA 2018

[26] N Zhang C Liu and B Chen ldquoA case study of presplittingblasting parameters of hard and massive roof based on theinteraction between support and overlying stratardquo Energiesvol 11 no 6 p 1363 2018

[27] Z T Zheng Y Xu J H Dong Q Zong and L P WangldquoHard rock deep hole cutting blasting technology in verticalshaft freezing bedrock section constructionrdquo Journal ofVibroengineering vol 17 no 3 pp 1105ndash1119 2015


[28] Z Zheng Y Xu D Li and J Dong ldquoNumerical analysis andexperimental study of hard roofs in fully mechanized miningfaces under sleeve fracturingrdquo Minerals vol 5 no 4pp 758ndash777 2015

[29] Z M Ma J Wang M C He Y B Gao J Z Hu and J WangldquoKey technologies and application test of an innovativenoncoal pillar mining approach a case studyrdquo Energiesvol 11 no 10 Article ID 2853 2018

[30] Q W Li L Qiao G Dasgupta S W Ma L P Wang andJ H Dong ldquoBlasting vibration safety criterion analysis withequivalent elastic boundary based on accurate loadingmodelrdquo Shock and Vibration vol 2015 Article ID 6046832015

[31] PWang L S Jiang J Q Jiang P Q Zheng andW 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 ArticleID 04017135 2018

[32] P Wang L S Jiang P Q Zheng G P Qin and C ZhangldquoInducing mode analysis of rock burst in fault-affected zonewith a hardndashthick stratum occurrencerdquo Environmental EarthSciences vol 78 p 467 2019

[33] F Meng H Zhou Z Wang et al ldquoExperimental study on theprediction of rockburst hazards induced by dynamic struc-tural plane shearing in deeply buried hard rock tunnelsrdquoInternational Journal of Rock Mechanics and Mining Sciencesvol 86 pp 210ndash223 2016

[34] L S Jiang P Wang P Q Zheng H J Luan and C ZhangldquoInfluence of different advancing directions on mining effectcaused by a faultrdquo Advances in Civil Engineering vol 2019Article ID 7306850 10 pages 2019

[35] C L Han Stress optimization and structure stability controlfor the surrounding rock of gob-side entry retaining PhDthesis China University of Mining and Technology BeijingChina 2013

[36] X G Ma M C He Z Li Y X Liu G Y Yu and H R DuldquoStudy on key parameters of roof cutting blasting design forself-formed roadway with composite roof without coal pillarrdquoJournal of China University of Mining amp Technology vol 48no 02 pp 236ndash277 2019

[37] J Q Tang W J Song L B Song and Z B Guo ldquoCuttingseam design and study of gob-side entry retaining by roofcutting and pressure reliefrdquo Safety in Coal Mines vol 47no 09 pp 53ndash59 2016

[38] X M Sun X Liu G F Liang D Wang and Y L Jiang ldquoKeyparameters of gob-side entry retaining formed by Roof cutand pressure releasing in thin coal seamsrdquo Chinese Journal ofRock Mechanics and Engineering vol 33 no 07 pp 1449ndash1456 2014


International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

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Hindawiwwwhindawicom Volume 2018


Active and Passive Electronic Components

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

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Journal of

Advances inOptoElectronics

Hindawiwwwhindawicom

Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

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Control Scienceand Engineering

Journal of



Journal ofEngineeringVolume 2018

SensorsJournal of



RotatingMachinery


Modelling ampSimulationin EngineeringHindawiwwwhindawicom Volume 2018


Chemical EngineeringInternational Journal of Antennas and

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Navigation and Observation


Hindawi

wwwhindawicom Volume 2018

Advances in

Multimedia

Submit your manuscripts atwwwhindawicom

location of the lower roof of the retaining roadway plays aguiding role for the entire roof of the gob-side entry (GSE)

When a hard thick main roof occurs over a coal seamwhere no immediate roof is present or the immediate roof isthinner the wall beside the roadway may have difficulty insupporting the hard roof -erefore it is necessary to presplitthe hard roof and to change the main roof structure thusresulting in effective pressure alleviation of the GSE [18ndash22]At present commonly used methods for roof presplitting areblasting presplitting and hydraulic fracturing [23 24] whichcan effectively cut off the overhanging roof above theretaining roadway and result in roof caving However whenusing hydraulic fracturing for a hard roof the mechanicalproperties of the roof decrease through the interaction of rockand water [25 26]-erefore blasting presplitting is generallyused for a hard roof -e traditional use of roof blasting andpressure relief is to advance the presplitting blasting on theroof which can speed up themovement and reduce the lengthof the cantilever block thus reducing the pressure and thedeformation of the surrounding rock In addition a verticalblastingmodel of bedrock was established through optimizingthe charge structure of borehole and then the influence ofblasting-hole diameter on the blasting effect is determined byusing a numerical simulation and field test [27 28] Cu-mulative blasting technology with directional presplittingunder composite-roof condition was adopted to effectivelycontrol the damage of roof and maintain the integrity of thecollapsed roof [29] A dynamic load numerical model whichregards artificial blasting as the earthquake source wasestablished in order to analyze the failure and deformation ofsurrounding rocks [30] However these previous studies donot consider the importance of the structure formed by roofcollapse and movement

Hence it is particularly important to select the bestcutting position (hole position) and angle (hole angle) whenpresplit blasting the roof to achieve better pressure-reliefeffects In this paper to control the large deformation of rocksurrounding the GSE the overlying structure and pressure-relief principle caused by roof cutting was first analyzed ATHAS mechanics model and a UDEC numerical model withregard to the overlying rock movement were established tostudy the relationship among the rotation angle of key blocksin THAS the width of the roadway and the wall force besideit and the optimal cutting position and cutting angle to revealthe pressure-relief effect of roof blasting and cutting and itsinfluence on the support stability of the roadway -e studyresults can provide a theoretical basis for reasonable technicalmeans and optimized supporting parameters in field obser-vation Moreover they have important application value forroof cutting and pressure relief using GSER technology

2 Analysis of Pressure Relief Caused by RoofBlasting and Cutting

21 Overburden Structure and Pressure-Relief PrincipleCaused by Roof Cutting When a hard thick main roofoccurs directly above a coal seam it is easily suspended at alarge scale owing to its high stiffness and strength whichresults in highly concentrated stress in the surrounding rock

of the roadway [31ndash34] Hence if the roof is presplit byblasting in a certain range outside the GSE the length of thecantilever block can be reduced and the caved rock block canbe squeezed and bitten with the noncaved block to form astable articulated structure thus reducing the pressure andalleviating the deformation of the rock surrounding the GSE

-e overburden structure after roof blasting was appliedis shown in Figure 1 As shown in Figure 1(a) the B2 block isrotated and its right side touches the floor first -e blockstill intersects with and presses against the B1 block to form abeam structure owing to the effect horizontal force and thefrictional resistance of joint-cutting -is results in loadexertion on the roadway and shows a poor pressure-reliefeffect In Figure 1(b) the key B2 block is completely cutdown after roof cutting and has lost mechanical trans-mission with the B1 block which has a short or even nocantilever However the position of roof cutting should notbe too close to the roadway in the field mainly because theblasting vibration caused by roof cutting will cause largedeformation of the rock surrounding the roadway InFigure 1(c) the key B2 block has subsided after roof cuttingand the B1 block is suspended for a certain length -en theB1 block was rotated and squeezed with the B2 block withface mining-is resulted in the formation of a three-hingedarch overlying structure transferred from the cantileverbeam structure and thus reduced the pressure of the wall andsurrounding rock

22 Determining Parameters of Roof Cutting According tothe aforementioned analysis the overlying structure afterroof cutting is very important for the stability of the sur-rounding rock in GSER technology -e basic parametersdetermining the overlying structure are the position and theangle of roof cutting

2210eoretical Analysis of Roof-Cutting Angle According tothe Voussoir beam theory [10] in order to ensure theslipping of block B2 the shear force must be greater than thefriction force between the two blocks as

R

Tge tan(φ minus β) (1)

where R is the shear force with the block failure N Tis horizontal force N and β is the angle of the roof cutting

-e possibility of slipping instability of the structureincreases with an increase in the cutting angle However thecutting angle should not be too large which may cause thedrill-hole depth to increase thus increasing the difficulty ofconstruction

222 0eoretical Analysis of Roof-Cutting Position If the B2block slips and loses stability after roof cutting the relationshipamong the rotation angle cutting angle and cutting position isdescribed by drawing a method according to the geometricrelationship of the blocks as shown in Figure 2 -e B1 blockrotated more easily and sank with a decrease in the cuttingangle then it made contact with the B2 block to form a THAS





Hard roof

Block A


Presplit


L1 L2

Coal

Floor

θ1θ2

(a)

Hard roof

Block A

Block B1

Block CBlock B2

Presplit


L1 L2

Coal

Floor

θ1

(b)

Hard roof

Block A

Block B1

Block CBlock B2

Presplit


L1 L2

Coal

Floor

θ1

(c)





1113944 MA 0e

2T +

12

qL12

minus fL1

minus P a + b +c

21113874 1113875 minus T(h minus m) 0

(2)





a + b +(c2) (3)


1113944 MA 012

qL12

minus P a + b +c

21113874 1113875 0 (4)

P qL1

2

2a + 2b + c (5)






L 2u

17

10z

u1113874 1113875

2+ 102

1113971

minus 10z

u⎛⎝ ⎞⎠ (6)


(RTq)



Block B1Block B2

L1

β

θ1

(a)

5 10 15 20 25

2

3

4

5

6

7

8

β (deg

)

L1 (m)



(b)




β (7)


(kEprimeI)









Poissonrsquosratio




load

h

m

a b c

C

B

A

q

TT

P

05eBlock B1

Block B2

L1

θ1


Block B1

q

P

a b c

L1

A













0 2 4 6 8 10 12 148 10 12 14

16 18 20 22

21 times 104

18 times 104

15 times 104

12 times 104

90 times 103

60 times 103

30 times 103

00

Supp

ort r

esist

ance

(N)



THASCantilever









Thickness

15m10m

16m

9m

9m3m

9m

10m

Lithology


sandstoneSandy

mudstoneSiltstone

CoalFine

sandstone

Andymudstone


0 1 2 3 4 5 6 7

3680

3660

3640

3620

3600

3580

3560

Supp

ort r

esist

ance

(N)


(a)

4800

4400

4000

3600

3200

280030 35 40 45 50 55 60 65

Supp

ort r

esist

ance

(kN

)

Roadway width (m)

(b)



(a) (b)

(c) (d)


(a) (b)

(c)

B1B2

Not contact

(d)







Backfill wall

Roof

CoalFloor


0000E + 00

(a)


0000E + 00

(b)


0000E + 00

(c)


0000E + 00

(d)


08

07

06

05

04

03

02

01

0000 05 10 15 20 25 30


Disp

lace

men

t (m

)













Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall




0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)









Backfill wall






150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





Hard roof

Block A


Presplit


L1 L2

Coal

Floor

θ1θ2

(a)

Hard roof

Block A

Block B1

Block CBlock B2

Presplit


L1 L2

Coal

Floor

θ1

(b)

Hard roof

Block A

Block B1

Block CBlock B2

Presplit


L1 L2

Coal

Floor

θ1

(c)





1113944 MA 0e

2T +

12

qL12

minus fL1

minus P a + b +c

21113874 1113875 minus T(h minus m) 0

(2)





a + b +(c2) (3)


1113944 MA 012

qL12

minus P a + b +c

21113874 1113875 0 (4)

P qL1

2

2a + 2b + c (5)






L 2u

17

10z

u1113874 1113875

2+ 102

1113971

minus 10z

u⎛⎝ ⎞⎠ (6)


(RTq)



Block B1Block B2

L1

β

θ1

(a)

5 10 15 20 25

2

3

4

5

6

7

8

β (deg

)

L1 (m)



(b)




β (7)


(kEprimeI)









Poissonrsquosratio




load

h

m

a b c

C

B

A

q

TT

P

05eBlock B1

Block B2

L1

θ1


Block B1

q

P

a b c

L1

A













0 2 4 6 8 10 12 148 10 12 14

16 18 20 22

21 times 104

18 times 104

15 times 104

12 times 104

90 times 103

60 times 103

30 times 103

00

Supp

ort r

esist

ance

(N)



THASCantilever









Thickness

15m10m

16m

9m

9m3m

9m

10m

Lithology


sandstoneSandy

mudstoneSiltstone

CoalFine

sandstone

Andymudstone


0 1 2 3 4 5 6 7

3680

3660

3640

3620

3600

3580

3560

Supp

ort r

esist

ance

(N)


(a)

4800

4400

4000

3600

3200

280030 35 40 45 50 55 60 65

Supp

ort r

esist

ance

(kN

)

Roadway width (m)

(b)



(a) (b)

(c) (d)


(a) (b)

(c)

B1B2

Not contact

(d)







Backfill wall

Roof

CoalFloor


0000E + 00

(a)


0000E + 00

(b)


0000E + 00

(c)


0000E + 00

(d)


08

07

06

05

04

03

02

01

0000 05 10 15 20 25 30


Disp

lace

men

t (m

)













Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall




0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)









Backfill wall






150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia




1113944 MA 0e

2T +

12

qL12

minus fL1

minus P a + b +c

21113874 1113875 minus T(h minus m) 0

(2)





a + b +(c2) (3)


1113944 MA 012

qL12

minus P a + b +c

21113874 1113875 0 (4)

P qL1

2

2a + 2b + c (5)






L 2u

17

10z

u1113874 1113875

2+ 102

1113971

minus 10z

u⎛⎝ ⎞⎠ (6)


(RTq)



Block B1Block B2

L1

β

θ1

(a)

5 10 15 20 25

2

3

4

5

6

7

8

β (deg

)

L1 (m)



(b)




β (7)


(kEprimeI)









Poissonrsquosratio




load

h

m

a b c

C

B

A

q

TT

P

05eBlock B1

Block B2

L1

θ1


Block B1

q

P

a b c

L1

A













0 2 4 6 8 10 12 148 10 12 14

16 18 20 22

21 times 104

18 times 104

15 times 104

12 times 104

90 times 103

60 times 103

30 times 103

00

Supp

ort r

esist

ance

(N)



THASCantilever









Thickness

15m10m

16m

9m

9m3m

9m

10m

Lithology


sandstoneSandy

mudstoneSiltstone

CoalFine

sandstone

Andymudstone


0 1 2 3 4 5 6 7

3680

3660

3640

3620

3600

3580

3560

Supp

ort r

esist

ance

(N)


(a)

4800

4400

4000

3600

3200

280030 35 40 45 50 55 60 65

Supp

ort r

esist

ance

(kN

)

Roadway width (m)

(b)



(a) (b)

(c) (d)


(a) (b)

(c)

B1B2

Not contact

(d)







Backfill wall

Roof

CoalFloor


0000E + 00

(a)


0000E + 00

(b)


0000E + 00

(c)


0000E + 00

(d)


08

07

06

05

04

03

02

01

0000 05 10 15 20 25 30


Disp

lace

men

t (m

)













Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall




0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)









Backfill wall






150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



β (7)


(kEprimeI)









Poissonrsquosratio




load

h

m

a b c

C

B

A

q

TT

P

05eBlock B1

Block B2

L1

θ1


Block B1

q

P

a b c

L1

A













0 2 4 6 8 10 12 148 10 12 14

16 18 20 22

21 times 104

18 times 104

15 times 104

12 times 104

90 times 103

60 times 103

30 times 103

00

Supp

ort r

esist

ance

(N)



THASCantilever









Thickness

15m10m

16m

9m

9m3m

9m

10m

Lithology


sandstoneSandy

mudstoneSiltstone

CoalFine

sandstone

Andymudstone


0 1 2 3 4 5 6 7

3680

3660

3640

3620

3600

3580

3560

Supp

ort r

esist

ance

(N)


(a)

4800

4400

4000

3600

3200

280030 35 40 45 50 55 60 65

Supp

ort r

esist

ance

(kN

)

Roadway width (m)

(b)



(a) (b)

(c) (d)


(a) (b)

(c)

B1B2

Not contact

(d)







Backfill wall

Roof

CoalFloor


0000E + 00

(a)


0000E + 00

(b)


0000E + 00

(c)


0000E + 00

(d)


08

07

06

05

04

03

02

01

0000 05 10 15 20 25 30


Disp

lace

men

t (m

)













Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall




0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)









Backfill wall






150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia












0 2 4 6 8 10 12 148 10 12 14

16 18 20 22

21 times 104

18 times 104

15 times 104

12 times 104

90 times 103

60 times 103

30 times 103

00

Supp

ort r

esist

ance

(N)



THASCantilever









Thickness

15m10m

16m

9m

9m3m

9m

10m

Lithology


sandstoneSandy

mudstoneSiltstone

CoalFine

sandstone

Andymudstone


0 1 2 3 4 5 6 7

3680

3660

3640

3620

3600

3580

3560

Supp

ort r

esist

ance

(N)


(a)

4800

4400

4000

3600

3200

280030 35 40 45 50 55 60 65

Supp

ort r

esist

ance

(kN

)

Roadway width (m)

(b)



(a) (b)

(c) (d)


(a) (b)

(c)

B1B2

Not contact

(d)







Backfill wall

Roof

CoalFloor


0000E + 00

(a)


0000E + 00

(b)


0000E + 00

(c)


0000E + 00

(d)


08

07

06

05

04

03

02

01

0000 05 10 15 20 25 30


Disp

lace

men

t (m

)













Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall




0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)









Backfill wall






150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia








Thickness

15m10m

16m

9m

9m3m

9m

10m

Lithology


sandstoneSandy

mudstoneSiltstone

CoalFine

sandstone

Andymudstone


0 1 2 3 4 5 6 7

3680

3660

3640

3620

3600

3580

3560

Supp

ort r

esist

ance

(N)


(a)

4800

4400

4000

3600

3200

280030 35 40 45 50 55 60 65

Supp

ort r

esist

ance

(kN

)

Roadway width (m)

(b)



(a) (b)

(c) (d)


(a) (b)

(c)

B1B2

Not contact

(d)







Backfill wall

Roof

CoalFloor


0000E + 00

(a)


0000E + 00

(b)


0000E + 00

(c)


0000E + 00

(d)


08

07

06

05

04

03

02

01

0000 05 10 15 20 25 30


Disp

lace

men

t (m

)













Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall




0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)









Backfill wall






150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


(a) (b)

(c) (d)


(a) (b)

(c)

B1B2

Not contact

(d)







Backfill wall

Roof

CoalFloor


0000E + 00

(a)


0000E + 00

(b)


0000E + 00

(c)


0000E + 00

(d)


08

07

06

05

04

03

02

01

0000 05 10 15 20 25 30


Disp

lace

men

t (m

)













Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall




0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)









Backfill wall






150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia






Backfill wall

Roof

CoalFloor


0000E + 00

(a)


0000E + 00

(b)


0000E + 00

(c)


0000E + 00

(d)


08

07

06

05

04

03

02

01

0000 05 10 15 20 25 30


Disp

lace

men

t (m

)













Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall




0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)









Backfill wall






150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia










Stre

ss (M

Pa)

0

5

10

15

20

25

30

Gob-sideentry

Backfillwall




0 1 2 3 4 501

02

03

04

05

06

07

08

Disp

lace

men

t (m

)









Backfill wall






150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





150m

51 913


Gob-side entry



Gob


350

300

250

200

150

100ndash20 ndash10 0 10 20 30 40 50 60


Anc

hor-

cabl

e for

ce (k

N)

A4A2

A7





6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia




6 Conclusions






Data Availability




0

10

20

30

40

4 16 28 40 52 64 76 88 100

Supp

ort p

ress

ure (

MPa

)








3 50 31 17351 40 19 25991 44 26 212


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


Acknowledgments


References











































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia
















RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


AnalysisofOverburdenStructureandPressure-ReliefEffectof...

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