Study on Surrounding Rock Deformation Mechanism and

Research ArticleStudy on Surrounding Rock Deformation Mechanism andControl of Roadway with Large Section and Extra-Thick Top Coal

Yuliang Yang 12 Xiaobin Li 1 and Pengfei Li1

1School of Energy and Mining Engineering China University of Mining and Technology (Beijing) Beijing 100083 China2School of Coal Engineering Shanxi Datong University Datong 037003 Shanxi China

Correspondence should be addressed to Yuliang Yang 250219035qqcom and Xiaobin Li lxb162197126com

Received 10 November 2020 Revised 18 December 2020 Accepted 4 March 2021 Published 19 March 2021

Academic Editor Roger Serra

Copyright copy 2021 Yuliang Yang et al 0is 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 order to solve the problem of safe and rapid excavation and support of roadway with large section and extra-thick top coalunder complex geological conditions the deformation mechanism and control of roadway are analyzed by means of fieldinvestigation numerical simulation theoretical analysis and field practice taking the 2203 transportation roadway of a mine inShanxi Province as the engineering background 0e results show the following (1) the concentration of normal tensile stress inthe middle of large-span roadway roof and end shear stress is significant which may easily lead to the separation of roof and theextrusion deformation of surrounding rock (2) the surface shear failure depth of the roadway side is large and the insufficientlength of the bolt the small density of the protective side and the insufficient support strength are easy to cause the bulge andsplitting of the coal wall (3) roof joints and fractures are developed and the dirt band of different thickness occurs so it is easy forthe roof separation and the anchor solids to cut down along the weak surface of the dirt band (4) the geological structure produceshorizontal movement of surrounding rock which easily leads to poor supporting effect of roadway roof and material deformationand failure Finally a safe and economic comprehensive support system of ldquohigh-strength high-resistance and high-prestressedanchor cable support system+high-strength support of the two sides roadway +U-shaped anchor cable combined trussrdquo isproposed and the control mechanism is explained and applied successfully in the field

1 Introduction

In recent years with the continuous improvement of keytechnology of large mining height fully mechanized top coalcaving mining in extra-thick coal seam and the rapid de-velopment of mine mechanical and electrical equipment[1 2] the kind of mining technology characterized by largemining face extra-thick coal seam and rapid advance speedhas been gradually developed and popularized and largesection roadway has been applied However due to thecomplex geological structure developed joints and fissuresthe occurrence of multilayer dirt band and the high miningintensity abnormal ground pressure behavior and otherfactors roadway deformation and damage is severe (roof falland separation) which seriously restricts the safety andefficient production of the mine 0erefore in order to solvethe technical problems there is an urgent need to find a safeefficient and rapid way about how to excavate and support

in the large section and extra-thick coal seam under complexgeological conditions

Scholars at home and abroad have done a lot of re-searches on deformation and failure mechanism and controlin the large section and thick coal seam roadway By ana-lyzing the stress change of surrounding rock and environ-ment Gao et al [3] determined the influencing factors andregional scope of stress concentration in dynamic pressureroadway and proposed strengthening support in key areasand accelerating the advancing speed of working face toreduce the influence of mining dynamic pressure onroadway Chu et al [4] studied the mechanism and controlmethod of large deformation of roadway in extra-thick coalseam in Lu Xin mining area and put forward an integratedsupport system with strong support surface and hightoughness which takes improving the elongation and im-pact toughness of supporting materials and increasing thesurface area and stiffness of supporting components as the

HindawiShock and VibrationVolume 2021 Article ID 6618424 11 pageshttpsdoiorg10115520216618424

core Yang et al [5] analyzed the surrounding rock mi-gration law of large cross section coal roadway with com-posite roof in extra-thick coal seam and the stress conditionof bolt cable of roadway roof and proposed the steppedsupport technology of bolt and anchor cable Yu et al [6]optimized the roadway support parameters of super-thickcomposite top coal and put forward the high-strengthcombined support method of long bolt and cable Wei et al[7ndash9] studied the roof asymmetric deformation and failurecharacteristics of gob side coal roadway in large section fullymechanized top coal caving face and put forward the sup-port countermeasures with ldquoasymmetric anchor beam trussrdquoas the core Xiao et al [10] analyzed the failure mode of thickroof coal roadway under deep mining conditions andproposed combining the support system of high-strengthand high-pretension bolt with cable-stayed anchor cablebeam and applied it in the field In terms of rapid excavationand support technology of roadway domestic and foreignscholars mainly do some researches on improving excava-tion equipment and optimizing auxiliary machinery andcompare the typical integration mode of excavation boltingand transportation [11ndash13] 0e above research results havelaid a certain foundation for surrounding rock deformationand control of large section coal roadway in extra-thick coalseam Generally speaking the research results mostly op-timize the support by increasing the bolt and cable supportdensity improving the strength of the support materialincreasing the length of the anchor or adding the sur-rounding rock control system combined with the defor-mation and failure characteristics of the surrounding rockHowever there are few reports on the rapid excavation andsupport of fully mechanized top coal caving roadway withlarge mining height under complex geological conditionswhich are characterized by ldquoanalyzing the failure mechanismof surrounding rock optimizing the control structure ofsurrounding rock and reducing the supporting materials forsurrounding rockrdquo

0is paper takes 2203 transportation roadway of a coalmine in Shanxi Province as the engineering backgroundcombined with the unique complex geological conditionsthe existing tunneling equipment and the original supportscheme in the process of excavation which show the phe-nomenon of severe deformation of surrounding rock largeconsumption of supporting materials complex excavationsupport and so on which lead to the imbalance of pro-duction 0rough field investigation numerical simulationand theoretical analysis the surrounding rock failuremechanism of large section roadway in extra-thick coal seamis analyzed Scientific safe and economic control measuresare proposed to realize the stability control of surroundingrock and safe and efficient support 0e research resultsprovide a reference for similar conditions of roadway ex-cavation support

2 Overview of the Project

21 General Situation of Engineering Geology 0e N8203working face of a coal mine in Shanxi is mainly mining coal3ndash5 with the buried depth of 350m 0ere are 6 layers of

carbonaceous mudstone and gangue with different thick-ness and the maximum thickness is about 05m 0e av-erage thickness of the coal seam is about 16m the averagedip angle is 3deg the strike length of the working face is 1250mand the inclined length is 210m 0e width of coal pillarbetween adjacent working faces is 20m 0e fracture jointsof top coal are abnormally developed and the Proctor co-efficient is 11 As shown in Figure 1 the immediate roof ofcoal seam is mudstone (18m) the basic roof is fine sand-stone (83m) the immediate floor is medium sandstone(21m) and the basic floor is medium fine sandstone (58m)2203 transportation roadway in N8203 working face is arectangular large section roadway with a width of 56m anda height of 37m 0e specific support scheme is shown inFigure 2

22 Deformation and Failure Characteristics of Roadway inOriginal Support Scheme With the support scheme inFigure 1 some phenomena are prone to occur in some areasof the roadway including the failure of W-shaped steel stripfalling off the roof roof bolt cutting and coal pillar sideswelling and splitting 0rough a large number of fieldobservations and analyses it is found that the deformationand failure of roadway are mainly characterized by hori-zontal extrusion dislocation deformation roof separationand coal side internal extrusion 0is can be summarized asfollows

221 Horizontal Extrusion Deformation of Top Coal 0ecombined action of high shear stress and horizontal com-pressive stress leads to the deformation of surrounding rockextrusion dislocation forming extrusion fracture zone 0eviolent horizontal movement of roof leads to the failure ofsupporting structure which is manifested as the bendingdeformation of W-shaped steel strip and the failure of roof(Figure 3(a))

222 Overall Slip and Dislocation of Multilayer Gangue0ere are many layers of gangue with different thicknesses inthe top coal structure It is quite common for the gangue tofall off from the upper layer in the process of excavation0en it is easy to cause the overall sliding and dislocation ofthe roof resulting in the cutting roof bolt or roof fallingaccident (Figure 3(b))

223 Side Heave Splitting Failure of Coal Pillar 0e twosides of the tunnel have the characteristics of splitting andflaky failure for many times and the large area of the overallmesh bag bulges at the side of the coal pillar resulting in theserious deformation of the metal mesh and the shear of thebolt at the side (Figure 3(c))

23 Roadway Deformation Observation In order to clarifythe supporting effect of the original support scheme afterthe formation of the roadway section the contact conver-gence measurement system is used to monitor the roadway

2 Shock and Vibration

surface displacement the roof separation meter is used tomonitor the roof separation amount and the bolt and cableaxial force is monitored by the bolt hydraulic pillow

A survey line is arranged at 600m away from theopening of the roadway to analyze the convergence ofsurrounding rock (Figure 4) In the initial stage theconvergence rate of the roof is faster than that of the twosides and the convergence rate of the roof and floor tends

to be stable after a higher step convergence and themaximum convergence amount is 295mm meanwhile theconvergence rate of the two sides increases linearly in theinitial and middle stages and tends to be stable and lagsbehind the roof and floor and the maximum convergenceamount is 375mm

Four different measuring points 1 2 3 and 4 arearranged at 150m 450m 750m and 1050m away from

readed steel bolt φ 22mm times 2400mm

Row spacing 1000mm times 1000mm

Cable φ 178mm times 8300mmRow spacing 2000mm times 2000mm

Steel mesh φ 6mm W-shaped steel stripRow 2000mm

Nylon net Steel mesh φ 6mm35

0020

05600

1200

1200

readed steel bolt φ20mmtimes 2200mm

Row spacing 1200mmtimes 1000mm

readed steel bolt φ22mm times 2200 mm


Unit mm

Figure 2 0e support scheme of 2203 transportation roadway

(a) (b) (c)

Figure 3 Actual picture of support failure of air return roadway of 2203 (a) Failure of W-shaped steel (b) Roof bolt cutting (c) Coal pillarbulge

Lithology ickness (m) Roof type

Fine sandstone 83 Basic roof

Mudstone 18 Immediate roof

Coal seam 16 Coal seam

Medium sandstone 21 Immediate floor

Medium fine sandstone 58 Basic floor

Figure 1 Generalized stratigraphy column of the working face

Shock and Vibration 3

the roadway to monitor the roof separation 0e statisticaldata are shown in Figure 5 After the excavation ofroadway the layer separation increases rapidly and tendsto be stable after 10 days of monitoring and the separationrange is 18mmndash481mm 0e bolt anchoring force of theroof and the two sides is monitored by the bolt hydraulicpillow As shown in Figure 6 the growth rate of theanchoring force of the roof bolt is faster than that of thetwo sides 0e maximum anchoring force of the top an-chor is 65 kN and the maximum anchoring force of theside anchor is 85 kN

According to the analysis of the above monitoringdata the deformation of the surrounding rock of the twosides of the roadway is large and the deformation rate isfast At the same time according to the field observationthe local area has the phenomena of swelling and splittingso the optimized scheme should strengthen the support ofthe two sides Under the premise of ensuring the overallstability of roadway the layout of roof anchor cableshould be adjusted to increase the support stability andreduce roof separation

3 Numerical Analysis of Surrounding RockStability of Roadway

According to the actual geological condition of 2203transportation roadway FLAC3D numerical calculationmodel is established to analyze the influence of different topcoal thickness and roadway width on surrounding rockstability and the stress state of support body in the originalsupport scheme 0e displacement boundary is adopted onthe left and right front and back and bottom surface of themodel the stress boundary is used on the upper part and theloading stress is the weight of overlying strata 0e modelsize is lengthtimeswidthtimes height 50mtimes 30mtimes 25m 0econstitutive relationship is based on the Mohr-Coulombmodel 0e material parameters of each rock stratum in thenumerical simulation are measured by the mechanics ex-periment of 2203 transportation roadway top and floor asshown in Table 1

31 2e Influence of Top Coal 2ickness and Roadway Widthon Surrounding Rock Stability

311 Influence of Top Coal 2ickness on Deformation andFailure of Roadway Surrounding Rock 0e simulationschemes with different top coal thickness of 4m 6m 8m10m 12m and 14m are designed to study the influence ondeformation and failure of surrounding rock withoutsupport

As shown in Figure 7 the convergence of roof and twosides increases linearly and monotonously with the increaseof top coal thickness At the same time the convergence rateof roof is faster than that of two sides and the thickness oftop coal has a strong influence on roof subsidence

0rough numerical simulation it is found that differenttop coal thicknesses have a greater impact on the plasticfailure of the roof but they have almost no impact on the twosides of the roadway and the floor 0ere is a small range oftensile stress in the middle of the roadway ledge and it can beapproximated that only the shear failure with a failure depthof 35m occurs on the surface of the roadway ledge As thethickness of the top coal increases the plastic failure range of

Conv

erge

nt d

efor

mat

ion

(mm

)

Convergence of top and bottomConvergence of wall rock

0

50

100

150

200

250

300

350

400

2 4 6 8 10 12 14 16 18 20 22 24 260Observation days

Figure 4 Convergence diagram of surrounding rock of roadway

Roof

sepa

ratio

n (m

m)

150m450m

750m1050m

3 5 7 9 11 13 151Observation days

05

101520253035404550

Figure 5 Roof separation of roadway

Anc

hore

d fo

rce (

kN)

RoofThe two sides roadway


0

10

20

30

40

50

60

70

80

90

Figure 6 Anchoring force of bolt


the roof changes from an ldquoinverted trapezoidrdquo shape to anldquoarch shaperdquo 0e reason is that when the thickness of the topcoal is small the coal-rock interface is prone to be separatedfrom the layer failing to form a falling arch 0e middleposition of the shallow part of the large-span roof is prone totensile failure and as the thickness of the top coal increasesthe shear failure gradually develops to the deep part

312 2e Influence of Roadway Width on the Stability ofSurrounding Rock 0e model assumes that the roadway is35m high and the top coal thickness is 12m Four differentroadway widths of 45m 55m 65m and 75m aredesigned to analyze the vertical stress distribution in themiddle of the roof under unsupported conditions

By analyzing the changes in vertical stress at differentpositions of the roof under different roadway spans thestress value gradually increases from 0MPa to the originalrock stress 0e vertical stress of the roof shows a downwardtrend as the width of the roadway increases With the in-crease of the roadway span the degree and scope of thedamage to the surrounding rock in the shallow part of theroof become larger

32 Force Analysis of Surrounding Rock Support Body inOriginal Support Scheme In order to further understand theunreasonable layout of the original support plan numericalsimulation of the original roadway support plan was carried

out0e stress of the anchor cable in the surrounding rock ofthe roadway was analyzed to lay the foundation for theoptimized design plan

321 Analysis of the Force of the Bolt After the roadway isexcavated the initial surface displacement change rate of theroadway is relatively large After the bolt support is rein-forced the axial force increases linearly and the supportstrength increases accordingly 0e degree of convergence ofthe roadway surface and the growth rate of the bolt axialforce show a downward trend 0e convergence of theroadway surface is similar to the parabolic growth 0e axialforce of the roadway bolt is distributed (Figure 8) 0e axialforce of the roof bolt of the roadway is smaller than that ofthe two sides of the roadway and the axial force of the bolt atthe shoulder and socket is smaller 0e axial force of theanchor rod in the middle of the two gangs decreases mo-notonously to the two ends and the peak value is located inthe middle of the right side of the roadway and its value is150 kN 0e peak axial force of the roof bolt is located at theposition of the anchor orifice and it decreases monoto-nously toward the depth According to the monitoring dataanalysis of bolt axial force the maximum value is 785 kNand the minimum value is only 335 kN 0e peak value ofthe bolt axial force at the roadway ledge is located at theshallow and middle part of the bolt Based on the aboveanalysis the optimization scheme should appropriately re-duce the roof bolt support density especially the supportdensity at the top corner Meanwhile the support strengthon both sides of the roadway should be strengthened andthe bolt with larger diameter and length should be selected

322 Analysis of Anchor Cable Stress As shown in Figure 9according to the distribution of the axial force of the anchorcable on the roof of the roadway the peak value of the axialforce is located at the anchor cable in the middle of the roofand the maximum value is 2131 kN 0e axial force of asingle anchor cable is distributed in a ldquobell shaperdquo with thepeak value at the central monitoring points 4 and 5 while thedeep and shallow monitoring points have the smallest axialforce 0erefore comprehensively considering the distri-bution of roof bolts and anchor cable axial forces the ar-rangement of roadway roof anchor cables should bereasonably selected to strengthen the support strength of theanchor cables in the middle of the roadway roof and reducethe amount of roof subsidence

0rough field investigation and numerical simulationthe failure mechanism of surrounding rock of the 2203transportation roadway is analyzed (1)0e concentration of

Table 1 Material parameters of each stratum in the model

Surrounding rock E (GPa) υ C (MPa) Ψ (deg) Ρ (Kgmiddotmminus3) Δ (MPa)Sandy mudstone 125 038 1634 236 1950 252Packsand 381 037 2025 354 2550 381Coal seam 546 035 587 153 1550 128Medium sandstone 428 035 2224 322 2650 418Middle-fine sandstone 381 041 2656 363 2750 538

Conv

erge

nt d

efor

mat

ion

(mm

)

Convergence of wall rockConvergence of top and bottom

6 8 10 12 144The thickness of the top-coal (m)

0

200

400

600

800

1000

1200

Figure 7 Convergence of surrounding rock with different top coalthickness


tensile stress and end shear stress appears in the middle ofthe roof of a large-span roadway It is easy to cause roofseparation and surrounding rock squeezing and dislocationdeformation (2) 0e surface of the two sides of the roadwayhas a large shear failure depth the length of the anchor boltsat the sides is less than the failure depth and the supportingdensity is small and the strength is low which is easy to causecoal wall bulge splitting (3) Roof joints and cracks aredeveloped and gangues of different thicknesses are presentwhich are prone to roof separation and anchor solids are cutoff along the weak surface of the gangue (4) 0e geologicalstructure induces the horizontal movement of surroundingrock resulting in poor support effect and material defor-mation failure

4 Control Strategy and Technology

41 Analysis of Control Countermeasures According to theanalysis of the failure mechanism of surrounding rock it isnecessary to optimize and adjust roof anchor cable roofangle anchor bolt and two sidesrsquo anchor bolt rationally inorder to realize the stability control of roadway with large

section of extra-thick top coal and at the same time to addreasonable support structure for roof separation roof cav-ing and horizontal movement On this basis a safe andeconomic comprehensive support system of ldquohigh-strengthhigh-resistance and high-prestress anchor cable supportsystem+ high-strength support of the two sides road-way +U-shaped anchor cable combined trussrdquo is proposed

(1) High-strength high-resistance and high-prestressyield anchor cable support system At present theoverall deformation of roadway is large the roof isdetached and the bolt cable fails On the premise ofmeeting the high support resistance the strength ofbolt and anchor cable should be increased At thesame time the support system allows certain de-formation which has the yield function to resist theinfluence of mining pressure near and on theworking face 20MnSi left-handed nonlongitudinalribbed high-strength (HRB500) and high-resistancebolt of 22mmtimes 2400mm was selected as the boltbody and the yield pressure tube and arch high-strength tray were matched with the yield pressuredistance of 35mm Birdrsquos nest anchor cable withdiameter of 178mm is selected to cooperate withdouble bubble yield pressure tube with pressurepoint of 21 tsim25 t and high-strength spherical tray0emetal mesh is made of cold drawn steel bars witha diameter of 60 mm

(2) High-strength support at the side 0e upper boltsupport system is adopted at side bolt At the sametime two rows of bolts at the upper shoulder socketof the original plan are arranged at side of roadway0e spacing between rows is changed from1200mmtimes 1000mm to 1000mmtimes 1000mm whichenhances the bolt length and increases the supportdensity and at the same time high pretension isapplied for timely support 0e bolt body is the sameas the roof support

(3) U-shaped anchor cable combined truss Originalroof anchor cable ldquofive-sided arrangementrdquo layoutchanged into ldquotwo-twordquo layout with a row spacingof 1500mm One row is between two W sectionsteel belts and the other row is at both ends of the W

Tension

Compression

Cable axial forceMagfac = 1000e + 000

Maximum = 1500e + 005

Figure 8 Distribution diagram of axial force of roadway bolt

Tension

Compression


Maximum = 2131e + 005

Figure 9 Distribution of axial force of anchor cable


section steel belts to replace the roof angle anchorrods (at an angle of 30deg with the vertical direction)for alternate support W-shaped steel strip 4shallow bolts and 2 deep anchor cables couplingsupport form U-shaped anchor cable combinedtruss 0e combination of high-strength high-re-sistance and high-prestress shallow bolt andW-shaped steel strip forms a stable bearing struc-ture with good integrity effectively controls thephenomenon of top coal crushing deformation andsurface stress concentration and achieves the effectof strong protective surface which can be defined asthe supporting system of first-level bolt compositebeam0e roof angle anchor cable on theW-shapedsteel strip anchors the support system at the deepstable place and the huge preload anchor cableeffectively controls the phenomenon of shear stressconcentration in the middle and end of the roof andlimits the horizontal slip and dislocation betweenthe weak surface layers of the gangue Acting at acertain angle on the deep stability of the two sides ithinders the top coal extrusion dislocation defor-mation to a certain extent It can prevent pullingfailure in the middle of top coal and protect loosecoal and rock mass Considering the overall supportscope the first-level composite beam support sys-tem can be defined as a ldquopalletrdquo with certainthickness and strength and the high-strength andhigh-prestress anchor cable at the end forms astrong locking structure under the bearing action ofW-shaped steel belt which can be defined as thesecond-level anchor cable support structure 0etwo-level support structure acts synergistically toform the U-shaped anchor cable combined trusssystem (Figure 10)

In the original support scheme the single anchor cableexerts a vertical upward force on the upper rock throughpoint contact and the surrounding rock cannot be in thethree-direction stress state and the radial support range islimited so it is difficult to effectively improve the stress stateof surrounding rock 0e anchor points of the U-shapedanchor cable combined truss are stable and in planar contactwith the roof of the roadway forming a closed bearingstructure with the deformation of the anchor solid andmaking the neutral axis of the anchor solid move down theanchor solid is in three-direction stress state in a widerrange and the horizontal deformation movement of thesurrounding rock is effectively controlled

42 Stability Analysis of Coal Strata under the Support ofU-ShapedAnchorCableCombinedTruss 0e roof rock layerof the roadway is a coal seam with an average thickness of12m 0e combined beam structure formed by the boltingsupport of a part of the coal seam at the lower part of the roofcan be approximately regarded as thin plate with elasticbody0e support strength provided by a single anchor cableis much larger than that of a single anchor bolt Since theroadway span is far less than the axial length it can be

approximately considered as a plane strain mechanicalmodel According to the mechanical analysis the combinedbeam structure of bolt support can be simplified into themodel of ldquosimply supported beamrdquo One end is supported bycoal pillar the other end is supported by solid coal and theend is suspended by two anchor cables anchored into thedeep stable place which is equivalent to adding two con-straints Figure 11 shows the model of ldquosecondary staticallyindeterminate beamrdquo [14]

As shown in Figure 11(b) symmetric semistructure canbe calculated and analyzed as the load bornes by both B andC are equal

δ11 δ22 l1 + l2

3EI (1)

δ12 δ21 l2

6EI (2)

Δ1p Δ2p minusq l1

3+ l2

31113872 1113873

24EI (3)

0e legislative equation of quadratic statically indeter-minate is

[δ] X + Δp1113966 1113967 Δ (4)

Substituting equations (1)ndash(3) into equation (4) thefollowing equation can be obtained

X1 X2 l13

+ l23

4 2l1 + 3l2( 1113857q (5)

where δii δij and Δip respectively represent the displace-ment generated by unit force Xi 1 Xj 1 and load actingalong the action direction at the action point of additionalunknown force Xi m Xi is the extra unknown force N EIrepresents the bending stiffness of the beam N middot m2 q

represents the uniform load on the beam l1 and l2 representthe support spacing l1 08m and l2 4m

According to the solution of force method in structuralmechanics the support reaction of B and C can be obtainedas follows

60degC60degC

W-shaped strap

First class bolt support system

U-shaped anchor cable truss

Anchor cable

Anchorbolt

Anchor cable

Figure 10 U-shaped anchor cable combined truss


YB YC 5l1

3+ 6l1

2l2 + l2

3

4 2l12

+ 3l1l21113872 1113873q (6)

Suppose the included angle between single anchor cableand vertical direction in the U-shaped anchor cable com-bined truss is α then the force along the direction of thesingle anchor cable of the truss is

Y1 YB

cos α (7)

In order to avoid large-scale roof separation and in-stability and caving accidents the minimum supportingforce of a single anchor cable per meter along the axialdirection of the roadway is as follows

Ymin Y1 26ch (8)

where c stands for the average unit weight of potential fallingrocks kNm3 taking 13 kNm3 and h is the potential fallingheight m

In the support scheme the diameter of anchor cable is178mm and the maximum supporting force provided byanchor cable can reach 463kN After the optimization of thescheme the row spacing of the U-shaped anchor cable com-bined truss is 2m so the control range of a single anchor cablein the axial direction of the roadway is 2m and the supportingforce provided per meter is 2315 kN 0e potential fallingheight is calculated by numerical simulation and themaximumvalue is about 6m According to formula (8) the minimumsupporting force required to be provided by a single anchorcable in each meter along the axial direction of the roadway is2028 kN which is less than the supporting force provided by asingle anchor cable in eachmeter along the axial direction of theroadway which is 2315 kN 0erefore the U-shaped anchorcable truss can control the stability of roof rock

5 Optimization of Support Scheme andField Measurement

51 Optimal Design of Support Scheme According to theabove analysis and considering the economic and constructioncosts the optimized scheme (Figure 12) is implemented in the2205 transportation roadway in the next working face

52 Optimization of Support Technology In order to realizethe fast support of large section coal roadway the support isdivided into two times by using the technique of letting the

pressure divide the support For the first time the roofW-shaped steel belt anchor rod anchor cable and two upperbolts on each row of the two sides are installed 0e secondsupport adopts the 20m position of lag heading face and theanchor cable between the W-shaped steel belt and two boltson the lower part of the two sides is installed 0e firstsupport is timely supported along with the roadway ef-fectively controlling the roof separation After the roofpressure is released the anchor cable and bolt under the endare strengthened for a second time It can not only effectivelycontrol the stability of the surrounding rock of the roof butalso realize parallel operation and speed up roadwayexcavation

0e field test shows that the optimized supportingscheme and construction technology can effectively solve theproblems of surrounding rock failure and slow supporting inroadway After optimization the plan is compared with theoriginal plan0e two roof angle bolts of roadway section aretransferred to two sides for installation In this processsupport time is saved about 210min per 100m Anchor cableis installed in the steel belt hole instead of bolt 4 bolts and 2anchor cables are saved in every 6 rows and 2628min issaved in support per 100m At the same time multi-procedure parallel operation is more conducive to the re-alization of digging and supporting balance 0e original2203 transportation roadway has an average footage of201m per month while the optimized scheme has an av-erage footage of 321m per month an increase of nearly 60

53 FieldMeasurement Analysis To verify the support effectof the new scheme a vertical hole is made for every 80malong the direction of the opening between 2205 transportroadway and the roadway and a total of 3 holes are arrangedEach hole is equipped with two sets of roof separation in-struments0e deep base points are arranged at 7m from theroof and the shallow base points are arranged at 25m fromthe roof

As shown in Figure 13 the maximum amount of dis-sociation of the top plate of the 1 2 and 3 measurementstations is 1mm 2mm and 3mm respectively By analyzingthe swelling instability of surrounding rock it can beconsidered that the roof has no separation phenomenonAccording to the surface displacement observation therelative displacement of roof floor and two sides is within acontrollable range which indicates that the supportingstrength of bolt and cable is reasonable and the deformationand failure of surrounding rock are effectively controlled

A B C D

l1 l2 l1

q

(a)

ABrsquo Brdquo C

D

X1q q

(b)

Figure 11 Simplification and calculation of roadway surface layer (a) Simplified model of roof surface layer (b) Calculation model ofsecondary statically indeterminate beam


Conv

erge

nt d

efor

mat

ion

(mm

)

Within the anchorage rangeOutside the anchorage rangee total amount of abscission layer

5 10 15 20 250Observation days

ndash02

03

08

13

18

(a)



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

(b)

Figure 13 Continued

Glass reinforced plasticbolt φ 22mm times 2400mm


readed steel bolt φ22mm times 2400mm


Cold drawn steel coils φ 6mm

Grids 80mm times80mm

W-shaped steel strip Row 1000mm

Plastic tray150mm times 150mm

times 10mm

3500

200

1000

1000

1000

5600

1000

1000

1000

60deg 60deg

Arched tray150mm times 150mm times 10mm

Metal plate300mm times 300mm times

20mm

High strength polyester fiber meshGrids 50mm times 50mm


readed steel bolt φ 22mm times 2400mmRow spacing 1000mm times 1000mm

Unit mm

Figure 12 Supporting section diagram of 2205 transportation roadway


6 Conclusion

(1) Field investigation and numerical simulation resultsshow that significant stress concentration unrea-sonable support parameters support structure andcomplex geological conditions are the main reasonsfor the failure and deformation of surrounding rock

(2) A safe and economic comprehensive support systemof ldquohigh-strength high-resistance and high-pre-stress anchor cable support system+ high-strengthsupport of the two sides roadway +U-type anchorcable combined trussrdquo is proposed Reasonablesupport structure is added for roof separation roofcaving and horizontal movement

(3) 0e new support system effectively controls thefailure and deformation of surrounding rocks andimproves the excavation support efficiency 0e fieldmeasurement results show that the average footageof the optimized scheme is 321m per month and theroadway rate is increased by 60

Data Availability

0e data used to support the findings of this research areincluded within the paper

Conflicts of Interest

0e authors declare that they have no conflicts of interest

Acknowledgments

0e authors gratefully acknowledge the financial support bythe Key RampD Program of Datong City Shanxi Province(2019025) and the program of Shanxi Natural Foundation ofChina (201901D111305)

References

[1] J H Wang ldquoKey technology for fully-mechanized top coalcaving with large mining height in extra-thick coal seamrdquoJournal of China Coal Society vol 38 no 12 pp 2089ndash20982013

[2] HM Li D J Jiang and D Y Li ldquoAnalysis of ground pressureand roof movement in fully-mechanized top coal caving withlarge mining height in ultra-thick seamrdquo Journal of china CoalSociety vol 39 no 10 pp 1956ndash1960 2014

[3] F Q Gao J S Xue and X W Yin ldquoStudy on the law ofdynamic pressurerdquo Coal Science and Technology vol 43 no 1pp 28ndash32 2015

[4] X W Chu Y Z Wu and M Shi ldquoLarge deformationmechanism and control technology of jointed brittle and extrathick coal seam roadwayrdquo Coal Science and Technologyvol 46 no 12 pp 98ndash106 2018

[5] Q S Yang S Li M S Gao et al ldquoLarge section and thick layercomposite roof coal roadway top supporting technologyrdquoCoal Mine Safety vol 46 no 7 pp 102ndash108 2015

[6] Y J Yu Y Zhao Y X Hao et al ldquoOptimization of supportparameters of large section coal roadway with huge thickcomposite roof coalrdquo Journal of Liaoning University of En-gineering and Technology vol 30 no 5 pp 693ndash696 2011

[7] Z Wei F L He G C Zhang et al ldquoFailure mechanism andcable truss control of large-scale section gob-side entry roofwith fully-mechanized cavingrdquo Journal of Mining amp SafetyEngineering vol 34 no 1 pp 1ndash8 2017

[8] G C Zhang and F L He ldquoAsymmetric failure and controlmeasures of large cross-section entry roof with strong miningdisturbance and fully-mechanized caving miningrdquo ChineseJournal of Rock Mechanics and Engineering vol 35 no 4pp 806ndash818 2016

[9] G C Zhang and F L He ldquoPillar width determination andsurrounding rocks control of gob-side entry with large cross-section and fully-mechanized miningrdquo Rock and Soil Me-chanics vol 37 no 6 pp 1721ndash1736 2016

[10] T Q Xiao J B Bai X Y Wang et al ldquoStability principle andcontrol of surrounding rock in deep coal roadway with large



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)

Figure 13 Roof separation of the station (a) 1 measurement station (b) 2 measurement station (c) 3 measurement station


section and thick top-coalrdquo Rock and Soil Mechanics vol 32no 6 pp 1874ndash1880 2011

[11] Z G Zhang ldquoDevelopment trend and key technology of coallane rapid driving systemrdquo Coal Science and Technologyvol 44 no 1 pp 55ndash60 2016

[12] H Zhao ldquoCurrent situation and Prospect of rapid tunnelingtechnology of coal mine rock roadway in Chinardquo Coal Scienceand Technology vol 40 no 1 pp 5ndash7 2012

[13] Y D Liu J Lin J W Yang et al ldquoRapid excavation andsupport technology of super thick coal roadway based on theintegration of excavation and anchoringrdquo Coal Science andTechnology vol 45 no 10 pp 60ndash65 2017

[14] Y F Zeng Y P Wu X P Lai et al ldquoAnalysis of roof cavinginstability mechanism of large section roadway under com-plex conditionsrdquo Journal of Mining amp Safety Engineeringvol 26 no 4 pp 423ndash427 2009


core Yang et al [5] analyzed the surrounding rock mi-gration law of large cross section coal roadway with com-posite roof in extra-thick coal seam and the stress conditionof bolt cable of roadway roof and proposed the steppedsupport technology of bolt and anchor cable Yu et al [6]optimized the roadway support parameters of super-thickcomposite top coal and put forward the high-strengthcombined support method of long bolt and cable Wei et al[7ndash9] studied the roof asymmetric deformation and failurecharacteristics of gob side coal roadway in large section fullymechanized top coal caving face and put forward the sup-port countermeasures with ldquoasymmetric anchor beam trussrdquoas the core Xiao et al [10] analyzed the failure mode of thickroof coal roadway under deep mining conditions andproposed combining the support system of high-strengthand high-pretension bolt with cable-stayed anchor cablebeam and applied it in the field In terms of rapid excavationand support technology of roadway domestic and foreignscholars mainly do some researches on improving excava-tion equipment and optimizing auxiliary machinery andcompare the typical integration mode of excavation boltingand transportation [11ndash13] 0e above research results havelaid a certain foundation for surrounding rock deformationand control of large section coal roadway in extra-thick coalseam Generally speaking the research results mostly op-timize the support by increasing the bolt and cable supportdensity improving the strength of the support materialincreasing the length of the anchor or adding the sur-rounding rock control system combined with the defor-mation and failure characteristics of the surrounding rockHowever there are few reports on the rapid excavation andsupport of fully mechanized top coal caving roadway withlarge mining height under complex geological conditionswhich are characterized by ldquoanalyzing the failure mechanismof surrounding rock optimizing the control structure ofsurrounding rock and reducing the supporting materials forsurrounding rockrdquo

0is paper takes 2203 transportation roadway of a coalmine in Shanxi Province as the engineering backgroundcombined with the unique complex geological conditionsthe existing tunneling equipment and the original supportscheme in the process of excavation which show the phe-nomenon of severe deformation of surrounding rock largeconsumption of supporting materials complex excavationsupport and so on which lead to the imbalance of pro-duction 0rough field investigation numerical simulationand theoretical analysis the surrounding rock failuremechanism of large section roadway in extra-thick coal seamis analyzed Scientific safe and economic control measuresare proposed to realize the stability control of surroundingrock and safe and efficient support 0e research resultsprovide a reference for similar conditions of roadway ex-cavation support

2 Overview of the Project

21 General Situation of Engineering Geology 0e N8203working face of a coal mine in Shanxi is mainly mining coal3ndash5 with the buried depth of 350m 0ere are 6 layers of

carbonaceous mudstone and gangue with different thick-ness and the maximum thickness is about 05m 0e av-erage thickness of the coal seam is about 16m the averagedip angle is 3deg the strike length of the working face is 1250mand the inclined length is 210m 0e width of coal pillarbetween adjacent working faces is 20m 0e fracture jointsof top coal are abnormally developed and the Proctor co-efficient is 11 As shown in Figure 1 the immediate roof ofcoal seam is mudstone (18m) the basic roof is fine sand-stone (83m) the immediate floor is medium sandstone(21m) and the basic floor is medium fine sandstone (58m)2203 transportation roadway in N8203 working face is arectangular large section roadway with a width of 56m anda height of 37m 0e specific support scheme is shown inFigure 2

22 Deformation and Failure Characteristics of Roadway inOriginal Support Scheme With the support scheme inFigure 1 some phenomena are prone to occur in some areasof the roadway including the failure of W-shaped steel stripfalling off the roof roof bolt cutting and coal pillar sideswelling and splitting 0rough a large number of fieldobservations and analyses it is found that the deformationand failure of roadway are mainly characterized by hori-zontal extrusion dislocation deformation roof separationand coal side internal extrusion 0is can be summarized asfollows

221 Horizontal Extrusion Deformation of Top Coal 0ecombined action of high shear stress and horizontal com-pressive stress leads to the deformation of surrounding rockextrusion dislocation forming extrusion fracture zone 0eviolent horizontal movement of roof leads to the failure ofsupporting structure which is manifested as the bendingdeformation of W-shaped steel strip and the failure of roof(Figure 3(a))

222 Overall Slip and Dislocation of Multilayer Gangue0ere are many layers of gangue with different thicknesses inthe top coal structure It is quite common for the gangue tofall off from the upper layer in the process of excavation0en it is easy to cause the overall sliding and dislocation ofthe roof resulting in the cutting roof bolt or roof fallingaccident (Figure 3(b))

223 Side Heave Splitting Failure of Coal Pillar 0e twosides of the tunnel have the characteristics of splitting andflaky failure for many times and the large area of the overallmesh bag bulges at the side of the coal pillar resulting in theserious deformation of the metal mesh and the shear of thebolt at the side (Figure 3(c))

23 Roadway Deformation Observation In order to clarifythe supporting effect of the original support scheme afterthe formation of the roadway section the contact conver-gence measurement system is used to monitor the roadway











0020

05600

1200

1200





Unit mm


(a) (b) (c)


















Conv

erge

nt d

efor

mat

ion

(mm

)


0

50

100

150

200

250

300

350

400



Roof

sepa

ratio

n (m

m)

150m450m

750m1050m


05

101520253035404550


Anc

hore

d fo

rce (

kN)



0

10

20

30

40

50

60

70

80

90













Conv

erge

nt d

efor

mat

ion

(mm

)



0

200

400

600

800

1000

1200










Tension

Compression


Maximum = 1500e + 005


Tension

Compression


Maximum = 2131e + 005








δ11 δ22 l1 + l2

3EI (1)

δ12 δ21 l2

6EI (2)

Δ1p Δ2p minusq l1

3+ l2

31113872 1113873

24EI (3)


[δ] X + Δp1113966 1113967 Δ (4)


X1 X2 l13

+ l23

4 2l1 + 3l2( 1113857q (5)




60degC60degC

W-shaped strap



Anchor cable

Anchorbolt

Anchor cable



YB YC 5l1

3+ 6l1

2l2 + l2

3

4 2l12

+ 3l1l21113872 1113873q (6)


Y1 YB

cos α (7)


Ymin Y1 26ch (8)










A B C D

l1 l2 l1

q

(a)

ABrsquo Brdquo C

D

X1q q

(b)



Conv

erge

nt d

efor

mat

ion

(mm

)



ndash02

03

08

13

18

(a)



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

(b)

Figure 13 Continued









times 10mm

3500

200

1000

1000

1000

5600

1000

1000

1000

60deg 60deg



20mm




Unit mm



6 Conclusion




Data Availability




Acknowledgments


References













Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)


















0020

05600

1200

1200





Unit mm


(a) (b) (c)


















Conv

erge

nt d

efor

mat

ion

(mm

)


0

50

100

150

200

250

300

350

400



Roof

sepa

ratio

n (m

m)

150m450m

750m1050m


05

101520253035404550


Anc

hore

d fo

rce (

kN)



0

10

20

30

40

50

60

70

80

90













Conv

erge

nt d

efor

mat

ion

(mm

)



0

200

400

600

800

1000

1200










Tension

Compression


Maximum = 1500e + 005


Tension

Compression


Maximum = 2131e + 005








δ11 δ22 l1 + l2

3EI (1)

δ12 δ21 l2

6EI (2)

Δ1p Δ2p minusq l1

3+ l2

31113872 1113873

24EI (3)


[δ] X + Δp1113966 1113967 Δ (4)


X1 X2 l13

+ l23

4 2l1 + 3l2( 1113857q (5)




60degC60degC

W-shaped strap



Anchor cable

Anchorbolt

Anchor cable



YB YC 5l1

3+ 6l1

2l2 + l2

3

4 2l12

+ 3l1l21113872 1113873q (6)


Y1 YB

cos α (7)


Ymin Y1 26ch (8)










A B C D

l1 l2 l1

q

(a)

ABrsquo Brdquo C

D

X1q q

(b)



Conv

erge

nt d

efor

mat

ion

(mm

)



ndash02

03

08

13

18

(a)



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

(b)

Figure 13 Continued









times 10mm

3500

200

1000

1000

1000

5600

1000

1000

1000

60deg 60deg



20mm




Unit mm



6 Conclusion




Data Availability




Acknowledgments


References













Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)

















Conv

erge

nt d

efor

mat

ion

(mm

)


0

50

100

150

200

250

300

350

400



Roof

sepa

ratio

n (m

m)

150m450m

750m1050m


05

101520253035404550


Anc

hore

d fo

rce (

kN)



0

10

20

30

40

50

60

70

80

90













Conv

erge

nt d

efor

mat

ion

(mm

)



0

200

400

600

800

1000

1200










Tension

Compression


Maximum = 1500e + 005


Tension

Compression


Maximum = 2131e + 005








δ11 δ22 l1 + l2

3EI (1)

δ12 δ21 l2

6EI (2)

Δ1p Δ2p minusq l1

3+ l2

31113872 1113873

24EI (3)


[δ] X + Δp1113966 1113967 Δ (4)


X1 X2 l13

+ l23

4 2l1 + 3l2( 1113857q (5)




60degC60degC

W-shaped strap



Anchor cable

Anchorbolt

Anchor cable



YB YC 5l1

3+ 6l1

2l2 + l2

3

4 2l12

+ 3l1l21113872 1113873q (6)


Y1 YB

cos α (7)


Ymin Y1 26ch (8)










A B C D

l1 l2 l1

q

(a)

ABrsquo Brdquo C

D

X1q q

(b)



Conv

erge

nt d

efor

mat

ion

(mm

)



ndash02

03

08

13

18

(a)



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

(b)

Figure 13 Continued









times 10mm

3500

200

1000

1000

1000

5600

1000

1000

1000

60deg 60deg



20mm




Unit mm



6 Conclusion




Data Availability




Acknowledgments


References













Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)



















Conv

erge

nt d

efor

mat

ion

(mm

)



0

200

400

600

800

1000

1200










Tension

Compression


Maximum = 1500e + 005


Tension

Compression


Maximum = 2131e + 005








δ11 δ22 l1 + l2

3EI (1)

δ12 δ21 l2

6EI (2)

Δ1p Δ2p minusq l1

3+ l2

31113872 1113873

24EI (3)


[δ] X + Δp1113966 1113967 Δ (4)


X1 X2 l13

+ l23

4 2l1 + 3l2( 1113857q (5)




60degC60degC

W-shaped strap



Anchor cable

Anchorbolt

Anchor cable



YB YC 5l1

3+ 6l1

2l2 + l2

3

4 2l12

+ 3l1l21113872 1113873q (6)


Y1 YB

cos α (7)


Ymin Y1 26ch (8)










A B C D

l1 l2 l1

q

(a)

ABrsquo Brdquo C

D

X1q q

(b)



Conv

erge

nt d

efor

mat

ion

(mm

)



ndash02

03

08

13

18

(a)



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

(b)

Figure 13 Continued









times 10mm

3500

200

1000

1000

1000

5600

1000

1000

1000

60deg 60deg



20mm




Unit mm



6 Conclusion




Data Availability




Acknowledgments


References













Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)
















Tension

Compression


Maximum = 1500e + 005


Tension

Compression


Maximum = 2131e + 005








δ11 δ22 l1 + l2

3EI (1)

δ12 δ21 l2

6EI (2)

Δ1p Δ2p minusq l1

3+ l2

31113872 1113873

24EI (3)


[δ] X + Δp1113966 1113967 Δ (4)


X1 X2 l13

+ l23

4 2l1 + 3l2( 1113857q (5)




60degC60degC

W-shaped strap



Anchor cable

Anchorbolt

Anchor cable



YB YC 5l1

3+ 6l1

2l2 + l2

3

4 2l12

+ 3l1l21113872 1113873q (6)


Y1 YB

cos α (7)


Ymin Y1 26ch (8)










A B C D

l1 l2 l1

q

(a)

ABrsquo Brdquo C

D

X1q q

(b)



Conv

erge

nt d

efor

mat

ion

(mm

)



ndash02

03

08

13

18

(a)



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

(b)

Figure 13 Continued









times 10mm

3500

200

1000

1000

1000

5600

1000

1000

1000

60deg 60deg



20mm




Unit mm



6 Conclusion




Data Availability




Acknowledgments


References













Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)














δ11 δ22 l1 + l2

3EI (1)

δ12 δ21 l2

6EI (2)

Δ1p Δ2p minusq l1

3+ l2

31113872 1113873

24EI (3)


[δ] X + Δp1113966 1113967 Δ (4)


X1 X2 l13

+ l23

4 2l1 + 3l2( 1113857q (5)




60degC60degC

W-shaped strap



Anchor cable

Anchorbolt

Anchor cable



YB YC 5l1

3+ 6l1

2l2 + l2

3

4 2l12

+ 3l1l21113872 1113873q (6)


Y1 YB

cos α (7)


Ymin Y1 26ch (8)










A B C D

l1 l2 l1

q

(a)

ABrsquo Brdquo C

D

X1q q

(b)



Conv

erge

nt d

efor

mat

ion

(mm

)



ndash02

03

08

13

18

(a)



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

(b)

Figure 13 Continued









times 10mm

3500

200

1000

1000

1000

5600

1000

1000

1000

60deg 60deg



20mm




Unit mm



6 Conclusion




Data Availability




Acknowledgments


References













Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)









YB YC 5l1

3+ 6l1

2l2 + l2

3

4 2l12

+ 3l1l21113872 1113873q (6)


Y1 YB

cos α (7)


Ymin Y1 26ch (8)










A B C D

l1 l2 l1

q

(a)

ABrsquo Brdquo C

D

X1q q

(b)



Conv

erge

nt d

efor

mat

ion

(mm

)



ndash02

03

08

13

18

(a)



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

(b)

Figure 13 Continued









times 10mm

3500

200

1000

1000

1000

5600

1000

1000

1000

60deg 60deg



20mm




Unit mm



6 Conclusion




Data Availability




Acknowledgments


References













Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)









Conv

erge

nt d

efor

mat

ion

(mm

)



ndash02

03

08

13

18

(a)



Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

(b)

Figure 13 Continued









times 10mm

3500

200

1000

1000

1000

5600

1000

1000

1000

60deg 60deg



20mm




Unit mm



6 Conclusion




Data Availability




Acknowledgments


References













Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)









6 Conclusion




Data Availability




Acknowledgments


References













Conv

erge

nt d

efor

mat

ion

(mm

)

ndash02

03

08

13

18

23

28

33

38

43

(c)















Documents

Study on Surrounding Rock Deformation Mechanism and