fracturingofthesoftrocksurroundingaroadwaysubjectedto … · 2020. 8. 25. ·...

Research ArticleFracturing of the Soft Rock Surrounding a Roadway Subjected toMining at Kouzidong Coal Mine

Zhili Su12 Wenbing Xie 1 Shengguo Jing2 Xingkai Wang2 and Qingteng Tang2

1State Key Laboratory of Coal Resources and Safe Mining China University of Mining and Technology Xuzhou 221116 China2School of Mines China University of Mining and Technology Xuzhou 221116 China

Correspondence should be addressed to Wenbing Xie tb17020012b0cumteducn

Received 10 September 2019 Revised 27 March 2020 Accepted 6 May 2020 Published 25 August 2020

Academic Editor Yuqing Zhang

Copyright copy 2020 Zhili Su et alis 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

e fracture development and distribution around the deep soft rock roadway are pivotal to any underground design In thispaper both field investigation and numerical simulation were taken to study the fracture evolution and rock deformation of a coalmine roadway at Kouzidong mine Fuyang Anhui Province China Based on the borehole imaging technique we found anasymmetric distribution of the fracture zone in the surrounding rock of the roadway By analyzing the C value of the fractures inthe borehole imageswe found that the fracture interval distribution of the surrounding rock of the tunnel the number of fractureswill fluctuate decrease with the increase of the depth To effectively study the fracture propagation and distribution of the roadwayunder longwall retreatment and roadway excavation the global-local numerical technique was applied via FLAC3D and PFC2DIn the roadway excavation process fractures were first formed in the shallow section of the roadway and progressively propagatedtoward the deeper soft rock layer the main failure mechanism was a tensile failure During longwall retreatment fracturescontinuously developed toward the deeper soft rock layer However the failure mechanism transformed to shear failure Fromnumerical results it can be seen that the stress concentration at the ribs was released which led to shear failure at the roof andfloor Due to the extensive tensile cracks in the shallow section the surrounding rock experienced expansion and fracture edeep shear failure also induced the formation of the nonadjacent crushing zone and elastic zone which is in line with the boreholeimaging results

1 Introduction

Due to the extensive exploitation of coal available resourcesat shallow depth quickly diminish and mining activitiesbelow 1000 meters have gradually gained popularity [1] emechanical behavior of the rock mass is closely related to themining method as the mining-induced stress redistributioncan significantly influence the surrounding rock mass [2]Compared with mining at shallow depth the failuremechanism and mechanical properties of the surroundingrock around roadway are different at deep mining locationswhere the large deformation and rheological phenomenonfrequently occur [3] e deformation of the surroundingrock is mainly due to the stress-induced fracture and ex-pansion To enhance the knowledge on the fracture distri-bution around the roadway and optimize the supporting

design it is pivotal to understand the crack development anddistribution of the surrounding rock around the roadway

To effectively study the fracture propagation around thesoft rock roadway a series of methods have been suggestedincluding field surveys [4] physical similarity modeling [5]and numerical simulations [6 7] Ma et al [8] used boreholeimaging geological radar roof separation monitoring andother means to study the fracture development process ofthe roadway roofey found that the crack opening and theseparation characteristic of this type of roadway are a dy-namic process gradually developing upwards Gao and Stead[9] used the discrete element model (DEM) to analyze therelationship between the major principal stress orientationand fracture distribution ey found that a roadway drivenat a large angle (75degndash90deg) with respect to the maximumhorizontal stress suffers significantly more fracturing than

HindawiAdvances in Civil EngineeringVolume 2020 Article ID 6858643 17 pageshttpsdoiorg10115520206858643

that driven at a small angle (0ndash15deg) With the development ofnumerical simulation theory the technique of couplingsimulation between the discrete element model (DEM) andthe finite element model (FEM) has been usedis couplingcalculation technique not only is more representative of themechanical properties of nonlinear rock materials but alsoconsiderably reduces the model computation time How-ever the combination of the two models is achieved by thedisplacement boundary conditions [10] where macro-properties of the material in both DEM and FEM have to besimilarWhen simulatingmultiple rock layers the numericalresults are not well aligned with field observations Toovercome the shortcomings of the coupling calculation thispaper implements the global-local simulation model eglobal-local model was originally used for the prediction ofthe stresses in hard rockmine [11 12] and it has been widelyused in solving rock mechanics problems

is paper investigated the fracture development anddeformation of the surrounding rock around the roadway atthe Kouzidong coal mine where fractures were observed andmonitored using borehole imaging at different locationsBased on the collected field data a numerical simulation viaPFC was also carried out to further investigate the failuremode and rock deformation around the roadway efindings of this study will help engineers to better under-stand the fracture distribution around the roadway andtherefore implement the appropriate supporting system

e introduction should be succinct with no sub-headings Limited figures may be included only if they aretruly introductory and contain no new results

2 Field Conditions at Kouzidong Coal Mine

21 Geological Conditions and Supporting SchemeKouzidong coal mine is located at YingdongDistrict FuyangCity Anhui Province as displayed in Figure 1 e longwallpanel for this study (121304 longwall face) locates at the westof the mining area and it the third fully mechanizedlongwall face of the 13-1 coal seam e longwall face isdivided into two parts based on the gas drainage roadwayand the south and north sections each section has a length of2474m and 350m respectively e total length of thelongwall panel is 11953m with an inclined depth of coverfrom 704m to 885me layout of the panel is illustrated inFigure 2 e roof of the longwall panel consists of mud-stone whereas the floor is composed of sandstone seeFigure 3 e two sides of the roadway are pillar and coal tobe recovered e roadway belongs to the deep buried solidcoal roadway with thick seam e roadway design is asemicircular arch with a 62m width and 45m height eillustration is displayed in Figure 4 together with the sup-porting scheme

22 Monitoring Stations To study the fracture developmentand distribution around the roadway under mining activitiesand dynamic loading two stations were installed at theroadway for monitoring purposes see Figure 2 e twomonitoring stations are 70m and 150m away from the

longwall space at the time of installation respectively Everystation contains 7 monitoring boreholes while station 2 alsohas 7 displacement meters the layout can be observed inFigure 5 Boreholes drilling into the roof have a length of10m whereas the boreholes at the ribs are 6m long Basedon the observation from the monitoring stations theroadway experienced significant deformation due to long-wall retreatment As a result the semicircular arch waspressured into a rectangular shape which can be seen inFigure 5 as well

221 Panoramic Digital Intelligent Borehole ImagingObservation e panoramic digital intelligent boreholeimaging system can transform a panoramic image into aplanar image through optical technology Based on thetechnology the panoramic image can either be processedinto 2D or 3D images e system can provide a 360degunfolding image of the borehole wall and can form a 3Dcolumnar borehole image

In this field test the ZKXG30 mine safe drilling tra-jectory detection device was used for monitoring shown inFigure 6 e device mainly consists of a color cameraprobe a video transmission line a guide bar a depthcounter and the main unit e front-view CCD camerahas a diameter of 22mm which can be used to observe theboreholes with diameters greater than 28mm and lengthsless than 30m e camera can detect the cracks that arelarger than 01mm and it is equipped with a high-pre-cision electronic compass with an angular resolution of01deg During monitoring the monitoring depth and imagecan be automatically combined by hand-held micro-receiver and the planar review of the borehole wall imagecan be synthesized in real time

According to the borehole imaging results the fracturedistribution location inclination angle and opening widthcan be estimated rough the observation of multipleboreholes the coalescence of the fractures and the fracturedistribution in larger zones can be analyzed to determine theextent of the loose zone around the roadway and the fracturelevel of the surrounding rock at different depths

Figure 1 Location of Kouzidong coal mine

2 Advances in Civil Engineering

222 Movement of the Surrounding Rock e displacementmeter was used to monitor the movement of the surroundingrock around the roadway which can reflect the degree of crack

opening and closing at different locations from the roadwaysurface KDW-1 type displacement meters were installed at theribs while KDW-2 type displacement meters were mounted at

Term

inal

min

ing

line

1213

04 w

orki

ng fa

ce1

N

Displacement monitoring station

Gob of 121303 coalface

Gas drainage roadway

2

Hau

lage

road

way

for m

uck

Machine roadway

Return-air roadwayMai

n ha

ulag

e roa

dway

Trac

k m

ain

haul

age r

oadw

ay

Figure 2 121304 longwall face schematic view

Column Lithology Thickness(m) Geologic description

Sandymudstone 290

Grey partial rust yellow blotch fractureand slide surface development

Finesandstone 29

Light gray fine-grained slow wavybedding dense and hard lithology

Sandymudstone 41


Siltstone 89Gray silty structure containing a small

amount of mud parallel joints

Mediumsandstone 53

Gray white mainly quartz medium grainstructure lithologic compact and hard

Finesandstone 43


Mudstone 121Black gray containing pyrite gentle slop

bedding

13-1 coal 49Black dark coal-based columnar and

powdery

Finesandstone 13


Sandymudstone 17



bedding

Sandymudstone 84


Finesandstone 51



bedding

Finesandstone 30


Figure 3 Geological structure at the mine site

Advances in Civil Engineering 3

the roof see Figures 7 and 8 respectively According to thesupport design of the roadway the installation points are de-termined to be 1m 2m 25m 3m and 6m from the ribs andthe installation points are 1m 2m 25m 4m and 9m awayfrom the roof 1 and 2 displacement meters were mounted inthe surrounding rock of the pillar side of the roadway 6 and 7displacement meters were positioned at the mining side of theroadway 3ndash5 were placed at the roof of the roadway asshown in Figure 5 again

3 Field Data Analysis

31 Deformation of the Surrounding Rock 2 displacementmeter aims tomonitor the deformation of the surrounding rockat different depths of the 121304 longwall face during the

mining processe deformation of the surrounding rock of theroadway can be represented by the displacement meter mea-surements e deformation of the rock mass between twoadjacent installation points can be expressed by the difference indisplacement between the two installation points

Figure 9 depicts an overview of the roadway section ex-axis represents the width of the roadway section the y-axisrepresents the height of the roadway section the z-axisrepresents the deformation of the rock mass between ad-jacent installation points of displacement meters and thecolor label indicates the compressive or tensile deformationof the rock mass As the color changes from purple to darkred the deformation of rockmass also increases accordinglye positions of cylinders in the figure indicate locations ofinstallation points in the surrounding rock and the height of

1400

800

6200

4500

1400

75iexclatilde

Bolt brvbar Otilde22iexcl Aacute2500

RibcablebrvbarOtilde218iexclAacute4100

Roof cable brvbar Otilde218iexcl Aacute9200

Unit mm

670

Figure 4 e primary support scheme

6m

6m

25m

1m2m

25m

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1

2

3 4

7

65

1m2m

25m3m

4m9m

2m

25m3m

4m9m

Base point of multipoint displacement meter

Figure 5 Borehole imaging tool locations and displacement meter locations


the cylinder denotes the amount of deformation of the rockmass while the color of the cylinder corresponds to differentdeformation intervals as shown in the color label Accordingto this diagram it is possible to analyze the deformation ofthe surrounding rock at different depths from the surface of

the roadway under the influence of the dynamic loadingcaused by longwall mining

Figure 9 also shows the relative displacement of thesurrounding rock at different depths from the surface of theroadway when station 2 is 130m 90m 50m and 10m

Figure 6 ZKXG30 mine safe drilling trajectory detection device

(a) (b)

Figure 7 KDW-1 displacement meter at the rib (a) displacement meter (b) installation at the rib

(a) (b)

Figure 8 KDW-2 displacement meter at the roof (a) displacement meter (b) installation at the roof


away from the longwall face From the figure the followingcan be seen (1) With the retreatment of the longwall facethere were extensive cracks quickly formed within 1m fromthe roadway surface the maximum deformation recordedwas 334mm ereby the deformation was also observedbetween 4 and 6m distance from the ribs with a maximumdeformation of 209mm (2) e deformation of the sur-rounding rock in the 2sim4m range of the roadway was lessthan other intervals and the surrounding rock deformationin between was mainly elastic deformation It shows that thesurrounding rock of the roadway can be divided into threezones from the surface ie crushing zone-elastic zone-crushing zone (3) Although the surrounding rock in therange of 4sim9m of the roadway roof has a larger deformationthan the surrounding rock in the range of 3sim4m it is still

under elastic condition (4) e deformation at the ribs isconsiderably higher than that of the roof indicating that thedeformation compatibility between the ribs and the roof andfloor of the roadway gradually deteriorates

From Figure 9 it can also be observed that the defor-mation in the ranges of 0sim1m and 4sim6m is higher sug-gesting that the fracture degree of the surrounding rockfracture is significantly larger than that of the adjacent zonesnear the surface of the roadway and within the supportingzone According to the bolt bearing arch theory [13] thecomposite material is formed by the rock bolts and thesurrounding rock such that the integrity and supporting ofrock in the range of the arch are better On the other handrock bolts are not anchored near the surface of the roadwaywhile the surrounding rock is also subjected to the tensile

350

300250200150100

50

ndash10

Width (m)

Roof surrounding rock

Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

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02

46

810

3900

Unit mm

34132925243819501463975048750000

12

10

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2

0

(a)

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ndash8ndash6

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Width (m)


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ive d

isplac

emen

t of a

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ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

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Unit mm

1261111039450787563004725315015750000

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(b)

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Width (m)


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ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

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46

810

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2370

Unit mm

20751780148511908950600030501000

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8

6

4

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0

(c)

350300250200150100

50ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

Unit mm

334029242508209116751259842542630000

12

10

8

6

4

2

0

(d)

Figure 9 Monitoring results from displacement meters at station 2 (a) 130m from the longwall face (b) 90m from the longwall face (c)50m from the longwall face (d) 10m from the longwall face


stress caused by the compression from the bolt ends istensile stress also aggravated the deformation and damage ofthe surrounding rock in this area

32 Fracture Development and Distribution of the Sur-rounding Rock After the excavation of roadway at deepcover depth surrounding fractures will be formed due tostress redistribution roadway advancement temperatureand humidity change e extent and degree of damage aswell as fracture evolution of the surrounding area can beevaluated to determine the stability and support design ofrock mass [14] When station 2 was 150m away from thelongwall surface we have got the borehole images which arenot influenced by longwall mining By comparing the crackdistribution at station 2 and station 1 the research pur-pose can be effectively studied

321 Analysis of Fracture Distribution in the SurroundingRock Based on two monitoring stations a total number of14 boreholes were collected with a total imaging length of108m According to the observation there are five kinds ofcracks in the surrounding rock of the roadway includingcrushing area circumferential crack longitudinal crackoblique crack and various cracks as shown in Figure 10

Figures 11 and 12 show borehole images collected from1 and 2 stations respectively e images were used tomonitor the influence of longwall retreatment (station2)and roadway excavation (station 1) on fracture distributionand development Figure 11 (1) is the 2D view of theborehole from 0 to 360deg whereas the zoomed-in views ofselected sections (red squares) can be observed in Figure 11(2) to study the detail of cracks Due to the integrity of othersections they were not analyzed in detail e length inFigure 11 (1) represents the distance from the surface of theroof to the imaging location For example 2m means thatthe distance from the roof of the roadway to the image is 2me distribution and development of the cracks in thesurrounding rock of the roadway can be seen from theborehole image

Figure 11 is the distribution and development of cracks inthe surrounding rock of the roadway arch under the influenceof excavation In the depth of 0ndash2m from the roadway archcracks fully developed into two crushing zones and the widthsof the crushing zones are 05m and 08m respectivelyereby there are also cracks that can be seen between 6 and8m whereas one fracture is parallel to the borehole axis Basedon the results it is clear that cracks only developed at shallowand deep locations from the roadway and cracks are moreintensive at the shallow location Other sections of the rockmass remained relatively competent and there were not anynoticeable cracks observed

Figure 12 is the distribution and development of cracksin the surrounding rock of the roadway arch under theinfluence of longwall retreatment Compared with theborehole results from station 2 the zone of cracks is largerin the shallow part of the surrounding rock ere were fivegroups of crushing zones observed in the borehole while theabscission layer was also found at the depth of 88m (the

white material was used for camera protection) Accordingto the enlarged view of the section it can be seen that denserfractures were formed in the surrounding rock e com-parison shows that the longwall retreatment facilitated thedevelopment of cracks inside the surrounding rock of theroadway arch

322 Analysis of Fracture Distribution in the SurroundingRock e value of the circularity (C) reflects the complexityof the boundary of the measured object Hence it was usedin this study to determine the boundary complexity of thefractures in the surrounding rock Based on the C-index ofthe surrounding rock at various borehole depths thethickness of the loose zone can be effectively identified [15]e C value can be estimated using the following equation

C P2

4πA (1)

where P is the perimeter of the surrounding rock crack andA is the area of the surrounding rock crack [16]

For example Figure 13 shows some typical fracturesobtained in station 2 and station 4 e numbers in thepictures represent the distance from the borehole surface tothe fracture location and the fractures were extracted by thegreyscale of the pixel in the picture P andA values from eachfigure can be estimated and used for the calculation of Cvalues of each crack

By analyzing the circularity C values of the surroundingrock fractures in each borehole the extent of the loose zoneand degree of fracture can be measured at station 2

In Figure 14 the x-axis is the distance of the crack fromthe borehole and the y-axis is the circularity C value of thecrack at this point

As depicted in Figure 14 there are spaces between thecolumns of data indicating that the cracks are not evenlydistributed and C values of cracks of the surrounding rock atdifferent depths are different Maximum C values appear atdifferent locations InterestinglyC values at deeper locationsfrom the roof are higher than those of the loose zone Resultshere show that at different depths the crushing zone andelastic zone were not adjacent to each other which may bedue to the zonal disintegration in the surrounding rock

Based on the results from station 1 it can be observedthat the distribution of C values is similar to station 2although fractures are less dense In conjunction with thedeformation behavior of the surrounding rock it is knownthat many fractures and compression occur at deep roadwayunder high dynamic pressure [17] ereby the crushingzones gradually develop and get wider such that the rockmass between these zones are compressed

rough field measurement and analysis it can be seenthat due to the longwall retreatment the surrounding stressstate is continuously changing where the surrounding rockalso deforms accordingly However at different depths thestress state fracture development and deformation aresignificantly different Since the fracture initiation and de-velopment cannot be monitored at all times further in-vestigation is carried out via numerical modeling


4 Numerical Simulation

To better simulate the crack distribution and development ofthe surrounding rock under the influence of dynamicpressure the simulation used the 3D global and discreteelement 2D local combination model e principal stress inthe direction of the roadway ahead of the longwall face wasextracted from the global model and then used as theboundary stress of the 2D model

e stress at the deep roadway is generally calculatedbased on the depth of cover and the empirical equationWhittanker and Potts [18] studied the stress around thelongwall face and found that the vertical stress ahead of thelongwall face increases first and then decreases to theoriginal stress level as the distance from the face increases

Compared with the theoretical analysis the discreteelement 3D model can better simulate the distribution anddevelopment of surrounding rock cracks during excavationHowever to accurately model the fracture development theparticle size in the numerical model must be very small ismeans that a significant number of particles are required toconstruct the model which makes the computation time toolong On the other hand if a 2D model is implemented theparticle size can be reduced while keeping the calculationtime short us the global-local model can yield bettersimulation results on the influence of longwall retreatmenton the fracture development around the roadway

41 Rock Mass and Material Properties To determine therock properties at different layers the geological strengthindex (GSI) method was used According to the ISRMstandard rock samples obtained from the mine site wereanalyzed to obtain the density uniaxial compressive strength

(a) (b) (c) (d) (e)

Figure 10 Crack types in the surrounding rock of the roadway (a) crushing area (b) circumferential crack (c) longitudinal crack (d)oblique crack (e) various cracks

00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m

Figure 11 Borehole imaging of borehole 4 at station 1 under theinfluence of excavation(1) the 2D view of the borehole from 0 to360deg (2) the zoomed-in views of selected sections

00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m

Figure 12 Borehole imaging of borehole 4 at station 2 under theinfluence of longwall retreatment (1) the 2D view of the boreholefrom 0 to 360deg (2) the zoomed-in views of selected sections


(a) (b) (c) (d) (e)

Figure 13 Crack characteristics (a) 012m (b) 156m (c) 242m (d) 612m and (e) 713m

Rdations of circular degree C

0

2

4

6

8

10

12

14

Rdat

ions

of c

ircul

ar d

egre

e C

1 2 3 4 5 60Depth in borehole (m)

(a)


0

5

10

15

20

25

Rdat

ions

of c

ircul

ar d

egre

e C


(b)


0

2

4

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8

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16

Rdat

ions

of c

ircul

ar d

egre

e C

2 4 6 8 100Depth in borehole (m)

(c)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(d)

Figure 14 Continued


σci internal friction angleΦmi Poissonrsquos ratio μ and elasticmodulus Ei see Table 1 However due to the preexistingdefects (such as joints cracks bedding and different mineralcompositions) in the rock mass the strength of the rockmass is lower than the rock strength measured in the lab-oratory erefore the specimen strength was converted tothe rock mass strength [19] e elastic modulus Emass wasthen calculated using the empirical formula proposed byHoek and Diederichs [20] e value of GSI was determinedaccording to the latest GSI value table [21] which gives theGSI reference value according to the rock type

Emass Ei 002 +1 minus (D2)

1 + e(60+15 Dminus GSI11)1113888 1113889 (2)

In the tableD which is the disturbance factor is assumedto be 0 according to the actual situation of the project ecalculation results are shown in Table 1

42 3D Global Model FLAC3D e FLAC3D with Mohr-Coulomb constitutive model was used for stress analysisahead of the longwall face e layout of the model can beseen in Figure 15 Since the monitoring stations were faraway from the initial gas drainage roadway the model onlysimulated the longwall face within the 300m from themonitoring stationse numerical longwall face is 300m inlength and 350m in width at the height of 177m To bettersimulate the stress around the gob area the low stiffnessmaterial was selected during model construction rather than


0

2

4

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16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


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Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)

Figure 14e distribution of C value at various borehole depths (a) borehole 1 at station 2 (b) borehole 2 at station 2 (c) borehole 3at station 2 (d) borehole 4 at station 2 (e) borehole 5 at station 2 (f ) borehole 6 at station 2 (g) borehole 7 at station 2


a blank space Kose and Cebi [22] suggested that the elasticmodulus of the material at gob is generally 15sim3500MPae elastic modulus has a great influence on the stressbehind the longwall face but it has less influence on the coalto be recovered [23] As this study only focused on thesection of the roadway where the coal was yet to be re-covered the elastic modulus of this part of the mesh was setto 250MPa and Poissonrsquos ratio was set to 025

e bottom boundary of the model is fixed and the topboundary is free to move whereas the other four boundariescan only roll in a vertical direction According to the depth ofcover of the upper boundary of the model vertical stress of1735MPa was applied and the stress coefficient was cal-culated according to the shallow crustal stress in the Chinesemainland [24]

06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)

where σH is the maximum horizontal principal stress σV isthe vertical stress H is the depth of cover and k is the stresscoefficient Given 800m depth of cover of the roadwayequation (4) estimated the k value to be 128

Based on different rock strata the mechanical propertiesare also different (Table 1) Gravity was applied to the modeland the model was processed until the equilibrium wasreached e space behind the longwall was then replacedwith the selected soft material e boundary stress of the 2Dmodel was recorded from the measuring point which was150m away from the longwall face From Figure 16 it can be

seen that during longwall retreatment the maximumstresses in z and x directions around the roadway reached206MPa and 2689MPa respectively Also the maximumstresses in z and x directions during roadway excavationreached 1642MPa and 2187MPa

43 2D Local Model PFC Due to the discontinuity of rockmaterials (such as joints cracks bedding and differentmineral compositions) some problems have arisen whenusing continuous media mechanics to analyze rock materialproperties Compared with the finite element model (FEM)the particle flow discrete element model (DEM) can providemore reliable simulations on the nonlinear mechanicalphenomena of rock fragmentation and deep roadway es-pecially the distribution and development of cracks in thesurrounding rock of deep roadway In this paper the Flat-Joint Model (FJM) proposed by Potyondy [25] was usedFigure 17 is a schematic diagram of the FJM (2D) An in-terface is created between two particles while particles onboth sides of the surface are in contact with the surface Atthe same time this interface is divided into multiple ele-ments and each element can be either bonded or unbondedAlthough the breakage of the bonding unit causes localdamage to the interface the interface can still resist bendingmoments Based on this microproperty the FJM canovercome the three shortcomings of the Bonded-ParticleModel [26] (1) the ratio between σci and tensile strength (σt)being smaller than the laboratory results (2) the extremelylow Φ and (3) the linearity of strength envelope By usingFTM more realistic macromechanical properties of the rockcan be constructed Since PFC uses a contact model and does

Table 1 Rock material and mass properties

LithologyRock specimens properties Rock mass properties

mi Density (kgm3) Poissonrsquos ratio Ei (GPa) GSI c (MPa) Tci (MPa) Φ (deg) Emass

Mudstone 5 2773 012 175 45 1174 373 1866 391Siltstone 9 2680 02 195 65 375 184 38 1232Sandstone 19 2681 026 56 35 1174 687 1866 63513-1 Coal 14 1329 036 175 30 457 163 3521 142Sandy mudstone 6 2510 015 1085 29 245 201 40 083Medium sandstone 15 2580 02 599 60 4 12 37 311Fine sandstone 17 2873 015 1085 55 375 184 375 443

Z

Y

X

ZX

200m

300m

600m

Figure 15 Global-local model


not have a suitable constitutive model to reflect the mac-roscopic mechanical parameters of the rock it is necessary tocalibrate its microparameters to characterize the macro-properties of the rock mass [25]

44 Model Calibration For brittle rock the appropriatemethodology to use microparameters to describe the mac-roproperties remains a concern in the field of geotechnical

engineering Currently the common way is to calibrate themicroparameters against themacroproperties collected fromexperimental results so that the synthetic rock sample issimilar to the actual rock sample from the field

emechanical properties of rock can be obtained by theuniaxial compressive tests including the peak strength σuelastic modulus E σt and μ see Table 2 For the sake ofsimplicity only Ec knks c and σc are generally modifiedduring the calibration process [26] Ec is the effective

16

σzzσxx

21

22St

ress

(MPa

)

ndash150 ndash100 ndash50 0 50 100ndash200Distance between the face and station (m)

(a)

σzzσxx

0 20 40 60 80 100 120 140 160 180ndash20Distance between the face and station (m)

16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)

Figure 16 Local model stress conditions from the global model (a) roadway excavation (b) longwall retreatment

Notional surfaces(faces)

Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)

Interface(deformable breakable partial damage)

Core Skirted face

Faced grain(rigid)

(b)

Figure 17 Flat-joint contact (left) (a) and flat-jointed material (right) (b) [26]


modulus of the bond knks is the stiffness ratio of the bond c

is the cohesion of the bond and σc is the tensile strength ofthe bond

In summary a standard rock model with a width of50mm and a height of 100mm was constructed in PFC eprocess involves (i) creation of walls at the boundaries of therectangular (ii) generation of particles at the radius from 03to 05mm within the walls until the porosity reaches 01 (iii)assigning FJM parameters to particle contacts and (iv) aservo-control mechanism [27] used to conduct the uniaxialcompressive test and direct tension test ere are 8773particles generated in a rock sample as displayed inFigure 18

e uniaxial compression calibration was carried outaccording to the ISRM standard with a loading speed of01mmmin e axial strain x1 and the transverse strain x2of the model were determined by recording displacements ofthe upper and lower walls and the gauge particles in themiddle of the model respectively e average force of theupper and lower walls was recorded to determine the load F

Based on the procedures which were suggested by WU[26] the calibrations of sandstone mudstone and coal wereachieved e proposed calibration process includes thefollowing

(1) UCSTS was satisfied by changing τcσc

(2) E and μ were calibrated by Ec and knks

(3) σc was initially determined by the direct tension testand then matched with σt

(4) c was modified to ensure that σu was reached

According to the process the microparameters wereobtained see Table 2 e stress-strain curve is displayed inFigure 18 e similarity between the simulation results andthe laboratory results was over 95 suggesting that cali-brations can be used for roadway model generation

45 Simulation of 121304 Longwall Panel e 121304longwall panel was constructed by using PFC (2D) as shownin Figure 19 e model dimensions are 51times 50m2 and itcontains 112684 particles Smaller radius particles weregenerated in the area of interest to study the rock behavior indetail whereas larger radius particles were generated nearthe boundaries to reduce the computation time e radiusof the particle was dependent on its location ie the distanceof the particle from the center of the roadway see Figure 20and Table 3 e ratio between Rmax and the radius ofsection (R) RmaxR was kept at 200 to ensure the consistencyof the model between different rock stratae vertical stresswas applied on the top wall while the horizontal stress was

applied on the sidewall e vertical displacement of thebottom wall was constrained e gravity was also applied tosimulate the field scenario closely By deleting particlesprogressively the roadway excavation could be mimickedsee Figure 19 Also biaxial loading was applied to simulatethe roadway excavation and longwall retreatment

As shown in Figure 19 the dip angle of the rock for-mation is 11deg and the position of the roadway is in line withthe field situation Dimensions of the roadway excavationare the same as the real conditions e section is a semi-circular arch with straight walls e arch radius is 31m theheight of the two ribs is 11m and the width is 62m

5 SimulationResults for FractureDevelopment

In field cases it has been approved that the roadway instabilityis directly related to the fracture development in the sur-rounding rock rough PFC23 the generation and devel-opment of cracks in the roadway excavation and longwallretreatment can be well studied Figures 21(a)sim21(c) show theexcavation process while Figures 21(d)sim21(f) illustrate theretreatment process In the figure the purple color represents atensile crack while the red color is a shear crack

According to Figure 21 it can be observed that after theroadway excavation tensile cracks dominated around theroadway Tensile cracks initially formed at the surface of theroadway and propagated toward deeper locations Howeverthe overall development direction of fractures is consistentwith the trend of rock strata is is because different rockshave different lithologies and fractures are preferred todevelop in weak rocks

Due to the disturbance of longwall retreatment thefracture development and crushing zone are significantlygreater than those of the roadway excavation Tensile cracksdeveloped from the ribs and propagated outwards in thehorizontal direction and shear cracks later formed in thedeeper locations With the stress relaxation due to frac-turing both roof and floor also experienced shear failure andeventually formed a pair of shear planes above the top of theroof e shear planes also developed in different directionswhich resulted in the net-like crushing zoneis agrees withresults from the field observation and the numerical sim-ulation of Gao [28]

e contact force chain is the interaction force between thecontact particles As shown in Figure 22 the greater the contactforce the darker the force chain color After the excavation ofthe section the failure of two ribs caused the stress to be re-leased rapidly see Figure 22(b) is led to the stress release atthe roof and floor of the roadway which redistributes thecontact force to deeper locations see Figure 22(c) e contact

Table 2 Macroparameter and microparameter calibration

LithologyMicroparameter Macroparameter

Density (kgm3) Ec (GPa) knks σc (MPa) tcσc σu (MPa) σt (MPa) E (GPa) μ UCSTSCoal 13293 175 10 306 822 1268 164 1546 036 775Mudstone 2773 2181 15 579 2129 3787 374 2626 012 1013Sandstone 26809 56 34 1297 5429 9198 687 577 026 1339


force within the rock depends on the rock strata so that thatinternal contact force is different layer by layer Finally thefracture degree of the surrounding rock is relatively high which

means that the contact force between the particles is almostzero is indicates that the ultimate bearing capacity of thesurrounding rock is negligible

(a)

0

20

40

60

80

100

CoalMudstoneSandstone

Stre

ss (M

Pa)

00 10 times 10ndash3 15 times 10ndash3 20 times 10ndash350 times 10ndash4

Strain

(b)

Figure 18 Simulated uniaxial compressive test (left) (a) and stress-strain curves for the rock (right) (b)

σzz

σxx σxx 45m

62m

Figure 19 Numerical model for the surrounding rock of working face machine lane

25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510

Figure 20 Particle distribution of the model


6 Conclusions

In this paper the mechanism of crack initiation and de-velopment under the influence of dynamic pressure in deepsoft rock roadway are studied e 121304 longwall face atKouzidong coal mine has a typical deep soft rock roadwaywhich was under the impact of the roadway excavation andthe longwall retreatment Based on the borehole imaging anddisplacement monitoring results the fracture development

and distribution under the dynamic pressure were analyzede mechanical properties of rock samples were collectedfrom the laboratory tests and downgraded by GSI to obtainthe rock mass properties FLAC3D was used to determinethe stress conditions for the PFC2D model during roadwayexcavation and longwall retreatment e microparametercalibration process was also discussed in the paper

Based on the field monitoring results it can be seen thatthe deformation of surrounding rock continuously increased

Table 3 Particle radius and distribution

Distribution range (m) 0sim51 51sim71 71sim101 101sim121 121simboundaryParticle radius (cm) 15sim225 21sim355 36sim505 39sim605 159sim255

7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )

Figure 21 e fracture distribution during roadway excavation and longwall retreatment

7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)

Figure 22 e contact force chain distribution during longwall retreatment


under the influence of dynamic pressure ereby the stressstate fracture development and deformation are consid-erably different at different depths

A PFC2Dmodel was constructed based on the geologicalconditions of the longwall face By applying different stressconditions fracture development and stress redistributionunder different scenarios were successfully replicated andanalyzed

Based on the results of field monitoring and numericalsimulation the mechanism and evolution of fracture de-velopment around deep soft rock roadway under dynamicpressure were revealed Cracks first appeared in the shallowsurrounding rock around the roadway and propagated to-ward the deeper soft rock layer due to the excavation-in-duced stress redistribution ereby rock around the ribsalso experienced stress relaxation while tensile cracksdominated around the roadway Under dynamic pressurecracks continuously propagated toward the soft rock layerHowever the failure mechanism transformed from tensile toshear failure Due to the stress relaxation of ribs the roadwayroof also failed and a pair of large shear failure planesintersected above the roof e rock mass between the roofand the shear planes is competent and unbroken At thesame time the stress relaxation zone kept expanding andhigh-stress concentration shifted to the deep section of thesurrounding rock

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to show gratitude to all those whohave helped them during the writing of this paper isresearch was funded by the National Key Research andDevelopment Plan (Grant no 2017YFC0603001) and theState Key Laboratory of Coal Resources and Safe MiningChina University of Mining and Technology (noSKLCRSM15X01)

References

[1] L Xu K Lu Y Pan and Z Qin ldquoStudy on rock burstcharacteristics of coal mine roadway in chinardquo Energy SourcesPart A-Recovery Utilization And Environmental Effectsvol 2019 pp 1556ndash7036 2019

[2] H Wagner ldquoDeep mining a rock engineering challengerdquoRock Mechanics and Rock Engineering vol 52 no 5pp 1417ndash1446 2019

[3] X Li F Gong M Tao et al ldquoFailure mechanism and coupledstatic-dynamic loading theory in deep hard rock mining areviewrdquo Journal of Rock Mechanics and Geotechnical Engi-neering vol 9 no 4 pp 767ndash782 2017

[4] M Gao W Jin R Zhang J Xie B Yu and H DuanldquoFracture size estimation using data frommultiple boreholesrdquo

International Journal of Rock Mechanics and Mining Sciencesvol 86 pp 29ndash41 2016

[5] M Bo J Hongwen C Kunfu and H Su ldquoFailure mechanismand stability control of a large section of very soft roadwaysurrounding rock shear sliprdquo International Journal of MiningScience and Technology vol 23 no 1 pp 127ndash134 2013

[6] Q Tang W Xie X Wang Z Su and J Xu ldquoNumerical studyon zonal disintegration of deep rock mass using three-di-mensional bonded block modelrdquo Advances in Civil Engi-neering vol 2019 Article ID 3589417 12 pages 2019

[7] A Lisjak D Figi and G Grasselli ldquoFracture developmentaround deep underground excavations insights from FDEMmodellingrdquo Journal of Rock Mechanics and GeotechnicalEngineering vol 6 no 6 pp 493ndash505 2014

[8] Z Ma Y Jiang W Du Y Zuo and D Kong ldquoFractureevolution law and control technology of roadways with extrathick soft roofrdquo Engineering Failure Analysis vol 84pp 331ndash345 2018

[9] F Gao and D Stead ldquoDiscrete element modelling of cutterroof failure in coal mine roadwaysrdquo International Journal ofCoal Geology vol 116 pp 158ndash171 2013

[10] M Cai P K Kaiser H Morioka et al ldquoFLACPFC couplednumerical simulation of AE in large-scale underground ex-cavationsrdquo International Journal of Rock Mechanics andMining Sciences vol 44 no 4 pp 550ndash564 2007

[11] C Edelbro ldquoNumerical modelling of observed fallouts in hardrock masses using an instantaneous cohesion-softeningfriction-hardening modelrdquo Tunnelling and UndergroundSpace Technology vol 24 no 4 pp 398ndash409 2009

[12] J Sjoberg and L Malmgren ldquoApplication of global-localmodelling to mining rock mechanics problemsrdquo in Pro-ceedings of the First International FLACDEM Symposium onNumerical Modeling pp 25ndash27 Minneapolis MN USAAugust 2008

[13] F Dong Support gteory Based on the Broken Rock Zone inSurround Rock China Coal Industry Publishing HouseBeijing China 2001

[14] M Cai and P K Kaiser ldquoAssessment of excavation damagedzone using a micromechanics modelrdquo Tunnelling and Un-derground Space Technology Incorporating Trenchless Tech-nology Research vol 20 no 4 pp 301ndash310 2005

[15] J Hongwen L Yuanhan and L Junqi ldquoBorehole cameratechnology for measuring the relaxation zone of surroundingrockmechanism and applicationrdquo Journal of China Universityof Mining amp Technology vol 38 no 5 pp 645ndash649 2009

[16] C Changxiu and J Qiong ldquoAlgorithm of circle analyse inimage processingrdquo Journal of Chongqing University (NaturalScience Edition) vol 28 no 11 pp 43ndash45 2005

[17] W Renhe and L Bin ldquoResearch on the phenomenon ofmultiple fracturing and fracture apertures of surroundingrock mass in deep roadwayrdquo Journal of China Coal Societyvol 35 no 6 pp 887ndash890 2010

[18] B N Whittaker and E L Potts ldquoAppraisal of strata controlpracticerdquo International Journal of RockMechanics andMiningSciences amp Geomechanics Abstracts vol 11 no 11 p A2251974

[19] B H D Brady and E T Brown ldquoEnergy changes accom-panying underground miningrdquo in Rock Mechanics for Un-derground Mining pp 240ndash259 Springer Berlin Germany1985

[20] E Hoek and M S Diederichs ldquoEmpirical estimation of rockmass modulusrdquo International Journal of Rock Mechanics andMining Sciences vol 43 no 2 pp 203ndash215 2006


[21] E Hoek T G Carter andM S Diederichs ldquoQuantification ofthe geological strength index chartrdquo in Proceedings of the 47thUS Rock MechanicsGeomechanics Symposium pp 8 SanFrancisco CA USA June 2013

[22] H Kose and Y Cebi ldquoInvestigation the stresses formingduring production of thick coal seamrdquo in Proceedings of the6th Coal Congress of Turkey Istanbul Turkey 1988

[23] G C Zhang F L He H G Jia and Y H Lai ldquoAnalysis ofgateroad stability in relation to yield pillar size a case studyrdquoRock Mechanics amp Rock Engineering vol 50 no 5 pp 1ndash162017

[24] J Feng S Qian and Z Yonghui ldquoResearch on distributionrule of shallow crustal geostress in China mainlandrdquo ChineseJournal of Rock Mechanics and Engineering vol 16 no 10pp 2056ndash2062 2007

[25] D Potyondy ldquoA flat-jointed bonded-particle material forhard rockrdquo in Proceedings of the 46th US Rock MechanicsGeomechanics Symposium Chicago IL USA June 2012

[26] S Wu and X Xu ldquoA study of three intrinsic problems of theclassic discrete element method using flat-joint modelrdquo RockMechanics and Rock Engineering vol 49 no 5 pp 1813ndash18302016

[27] D O Potyondy and P A Cundall ldquoA bonded-particle modelfor rockrdquo International Journal of RockMechanics andMiningSciences vol 41 no 8 pp 1329ndash1364 2004

[28] G Fu-Qjiang K Hongpu and L N Jian ldquoNumerical sim-ulation of zonal distrigation of surrounding rockrdquo Journal ofChina Coal Society vol 35 no 1 pp 21ndash25 2010


that driven at a small angle (0ndash15deg) With the development ofnumerical simulation theory the technique of couplingsimulation between the discrete element model (DEM) andthe finite element model (FEM) has been usedis couplingcalculation technique not only is more representative of themechanical properties of nonlinear rock materials but alsoconsiderably reduces the model computation time How-ever the combination of the two models is achieved by thedisplacement boundary conditions [10] where macro-properties of the material in both DEM and FEM have to besimilarWhen simulatingmultiple rock layers the numericalresults are not well aligned with field observations Toovercome the shortcomings of the coupling calculation thispaper implements the global-local simulation model eglobal-local model was originally used for the prediction ofthe stresses in hard rockmine [11 12] and it has been widelyused in solving rock mechanics problems

is paper investigated the fracture development anddeformation of the surrounding rock around the roadway atthe Kouzidong coal mine where fractures were observed andmonitored using borehole imaging at different locationsBased on the collected field data a numerical simulation viaPFC was also carried out to further investigate the failuremode and rock deformation around the roadway efindings of this study will help engineers to better under-stand the fracture distribution around the roadway andtherefore implement the appropriate supporting system

e introduction should be succinct with no sub-headings Limited figures may be included only if they aretruly introductory and contain no new results

2 Field Conditions at Kouzidong Coal Mine

21 Geological Conditions and Supporting SchemeKouzidong coal mine is located at YingdongDistrict FuyangCity Anhui Province as displayed in Figure 1 e longwallpanel for this study (121304 longwall face) locates at the westof the mining area and it the third fully mechanizedlongwall face of the 13-1 coal seam e longwall face isdivided into two parts based on the gas drainage roadwayand the south and north sections each section has a length of2474m and 350m respectively e total length of thelongwall panel is 11953m with an inclined depth of coverfrom 704m to 885me layout of the panel is illustrated inFigure 2 e roof of the longwall panel consists of mud-stone whereas the floor is composed of sandstone seeFigure 3 e two sides of the roadway are pillar and coal tobe recovered e roadway belongs to the deep buried solidcoal roadway with thick seam e roadway design is asemicircular arch with a 62m width and 45m height eillustration is displayed in Figure 4 together with the sup-porting scheme

22 Monitoring Stations To study the fracture developmentand distribution around the roadway under mining activitiesand dynamic loading two stations were installed at theroadway for monitoring purposes see Figure 2 e twomonitoring stations are 70m and 150m away from the

longwall space at the time of installation respectively Everystation contains 7 monitoring boreholes while station 2 alsohas 7 displacement meters the layout can be observed inFigure 5 Boreholes drilling into the roof have a length of10m whereas the boreholes at the ribs are 6m long Basedon the observation from the monitoring stations theroadway experienced significant deformation due to long-wall retreatment As a result the semicircular arch waspressured into a rectangular shape which can be seen inFigure 5 as well

221 Panoramic Digital Intelligent Borehole ImagingObservation e panoramic digital intelligent boreholeimaging system can transform a panoramic image into aplanar image through optical technology Based on thetechnology the panoramic image can either be processedinto 2D or 3D images e system can provide a 360degunfolding image of the borehole wall and can form a 3Dcolumnar borehole image

In this field test the ZKXG30 mine safe drilling tra-jectory detection device was used for monitoring shown inFigure 6 e device mainly consists of a color cameraprobe a video transmission line a guide bar a depthcounter and the main unit e front-view CCD camerahas a diameter of 22mm which can be used to observe theboreholes with diameters greater than 28mm and lengthsless than 30m e camera can detect the cracks that arelarger than 01mm and it is equipped with a high-pre-cision electronic compass with an angular resolution of01deg During monitoring the monitoring depth and imagecan be automatically combined by hand-held micro-receiver and the planar review of the borehole wall imagecan be synthesized in real time

According to the borehole imaging results the fracturedistribution location inclination angle and opening widthcan be estimated rough the observation of multipleboreholes the coalescence of the fractures and the fracturedistribution in larger zones can be analyzed to determine theextent of the loose zone around the roadway and the fracturelevel of the surrounding rock at different depths

Figure 1 Location of Kouzidong coal mine




Term

inal

min

ing

line

1213

04 w

orki

ng fa

ce1

N




2

Hau

lage

road

way

for m

uck

Machine roadway


n ha

ulag

e roa

dway

Trac

k m

ain

haul

age r

oadw

ay



Sandymudstone 290


Finesandstone 29


Sandymudstone 41




Mediumsandstone 53


Finesandstone 43



bedding


powdery

Finesandstone 13


Sandymudstone 17



bedding

Sandymudstone 84


Finesandstone 51



bedding

Finesandstone 30









1400

800

6200

4500

1400

75iexclatilde




Unit mm

670


6m

6m

25m

1m2m

25m

25m

25m

3m4m6m 1m 2m 3m 4m


1m2m

25m3m

4m9m

1

2

3 4

7

65

1m2m

25m3m

4m9m

2m

25m3m

4m9m








(a) (b)


(a) (b)






350

300250200150100

50

ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

3900

Unit mm

34132925243819501463975048750000

12

10

8

6

4

2

0

(a)

350

300250200150100

50

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

Unit mm

1261111039450787563004725315015750000

10

8

6

4

2

0

ndash10

(b)

350300250200150100

50ndash10

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

2370

Unit mm

20751780148511908950600030501000

10

8

6

4

2

0

(c)

350300250200150100

50ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

Unit mm

334029242508209116751259842542630000

12

10

8

6

4

2

0

(d)











C P2

4πA (1)














(a) (b) (c) (d) (e)


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m



(a) (b) (c) (d) (e)



0

2

4

6

8

10

12

14

Rdat

ions

of c

ircul

ar d

egre

e C


(a)


0

5

10

15

20

25

Rdat

ions

of c

ircul

ar d

egre

e C


(b)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(c)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(d)

Figure 14 Continued




1 + e(60+15 Dminus GSI11)1113888 1113889 (2)




0

2

4

6

8

10

12

14

16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


0

2

4

6

8

10

12

14

16

18

20

Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)





06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References


































Term

inal

min

ing

line

1213

04 w

orki

ng fa

ce1

N




2

Hau

lage

road

way

for m

uck

Machine roadway


n ha

ulag

e roa

dway

Trac

k m

ain

haul

age r

oadw

ay



Sandymudstone 290


Finesandstone 29


Sandymudstone 41




Mediumsandstone 53


Finesandstone 43



bedding


powdery

Finesandstone 13


Sandymudstone 17



bedding

Sandymudstone 84


Finesandstone 51



bedding

Finesandstone 30









1400

800

6200

4500

1400

75iexclatilde




Unit mm

670


6m

6m

25m

1m2m

25m

25m

25m

3m4m6m 1m 2m 3m 4m


1m2m

25m3m

4m9m

1

2

3 4

7

65

1m2m

25m3m

4m9m

2m

25m3m

4m9m








(a) (b)


(a) (b)






350

300250200150100

50

ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

3900

Unit mm

34132925243819501463975048750000

12

10

8

6

4

2

0

(a)

350

300250200150100

50

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

Unit mm

1261111039450787563004725315015750000

10

8

6

4

2

0

ndash10

(b)

350300250200150100

50ndash10

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

2370

Unit mm

20751780148511908950600030501000

10

8

6

4

2

0

(c)

350300250200150100

50ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

Unit mm

334029242508209116751259842542630000

12

10

8

6

4

2

0

(d)











C P2

4πA (1)














(a) (b) (c) (d) (e)


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m



(a) (b) (c) (d) (e)



0

2

4

6

8

10

12

14

Rdat

ions

of c

ircul

ar d

egre

e C


(a)


0

5

10

15

20

25

Rdat

ions

of c

ircul

ar d

egre

e C


(b)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(c)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(d)

Figure 14 Continued




1 + e(60+15 Dminus GSI11)1113888 1113889 (2)




0

2

4

6

8

10

12

14

16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


0

2

4

6

8

10

12

14

16

18

20

Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)





06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References





































1400

800

6200

4500

1400

75iexclatilde




Unit mm

670


6m

6m

25m

1m2m

25m

25m

25m

3m4m6m 1m 2m 3m 4m


1m2m

25m3m

4m9m

1

2

3 4

7

65

1m2m

25m3m

4m9m

2m

25m3m

4m9m








(a) (b)


(a) (b)






350

300250200150100

50

ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

3900

Unit mm

34132925243819501463975048750000

12

10

8

6

4

2

0

(a)

350

300250200150100

50

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

Unit mm

1261111039450787563004725315015750000

10

8

6

4

2

0

ndash10

(b)

350300250200150100

50ndash10

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

2370

Unit mm

20751780148511908950600030501000

10

8

6

4

2

0

(c)

350300250200150100

50ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

Unit mm

334029242508209116751259842542630000

12

10

8

6

4

2

0

(d)











C P2

4πA (1)














(a) (b) (c) (d) (e)


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m



(a) (b) (c) (d) (e)



0

2

4

6

8

10

12

14

Rdat

ions

of c

ircul

ar d

egre

e C


(a)


0

5

10

15

20

25

Rdat

ions

of c

ircul

ar d

egre

e C


(b)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(c)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(d)

Figure 14 Continued




1 + e(60+15 Dminus GSI11)1113888 1113889 (2)




0

2

4

6

8

10

12

14

16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


0

2

4

6

8

10

12

14

16

18

20

Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)





06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References




































(a) (b)


(a) (b)






350

300250200150100

50

ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

3900

Unit mm

34132925243819501463975048750000

12

10

8

6

4

2

0

(a)

350

300250200150100

50

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

Unit mm

1261111039450787563004725315015750000

10

8

6

4

2

0

ndash10

(b)

350300250200150100

50ndash10

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

2370

Unit mm

20751780148511908950600030501000

10

8

6

4

2

0

(c)

350300250200150100

50ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

Unit mm

334029242508209116751259842542630000

12

10

8

6

4

2

0

(d)











C P2

4πA (1)














(a) (b) (c) (d) (e)


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m



(a) (b) (c) (d) (e)



0

2

4

6

8

10

12

14

Rdat

ions

of c

ircul

ar d

egre

e C


(a)


0

5

10

15

20

25

Rdat

ions

of c

ircul

ar d

egre

e C


(b)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(c)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(d)

Figure 14 Continued




1 + e(60+15 Dminus GSI11)1113888 1113889 (2)




0

2

4

6

8

10

12

14

16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


0

2

4

6

8

10

12

14

16

18

20

Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)





06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References



































350

300250200150100

50

ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

3900

Unit mm

34132925243819501463975048750000

12

10

8

6

4

2

0

(a)

350

300250200150100

50

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

Unit mm

1261111039450787563004725315015750000

10

8

6

4

2

0

ndash10

(b)

350300250200150100

50ndash10

ndash8ndash6

ndash4ndash2

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

02

46

810

12

2370

Unit mm

20751780148511908950600030501000

10

8

6

4

2

0

(c)

350300250200150100

50ndash10

Width (m)


Relat

ive d

isplac

emen

t of a

djac

ent

met

ric p

oint

s (m

m)

Height

(m)

ndash8ndash6

ndash4ndash2

02

46

810

Unit mm

334029242508209116751259842542630000

12

10

8

6

4

2

0

(d)











C P2

4πA (1)














(a) (b) (c) (d) (e)


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m



(a) (b) (c) (d) (e)



0

2

4

6

8

10

12

14

Rdat

ions

of c

ircul

ar d

egre

e C


(a)


0

5

10

15

20

25

Rdat

ions

of c

ircul

ar d

egre

e C


(b)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(c)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(d)

Figure 14 Continued




1 + e(60+15 Dminus GSI11)1113888 1113889 (2)




0

2

4

6

8

10

12

14

16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


0

2

4

6

8

10

12

14

16

18

20

Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)





06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References








































C P2

4πA (1)














(a) (b) (c) (d) (e)


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m



(a) (b) (c) (d) (e)



0

2

4

6

8

10

12

14

Rdat

ions

of c

ircul

ar d

egre

e C


(a)


0

5

10

15

20

25

Rdat

ions

of c

ircul

ar d

egre

e C


(b)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(c)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(d)

Figure 14 Continued




1 + e(60+15 Dminus GSI11)1113888 1113889 (2)




0

2

4

6

8

10

12

14

16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


0

2

4

6

8

10

12

14

16

18

20

Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)





06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References





































(a) (b) (c) (d) (e)


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m


00m(1)

Borehole image

(2)

10m 20m 30m 40m 50m 60m 70m 80m 90m



(a) (b) (c) (d) (e)



0

2

4

6

8

10

12

14

Rdat

ions

of c

ircul

ar d

egre

e C


(a)


0

5

10

15

20

25

Rdat

ions

of c

ircul

ar d

egre

e C


(b)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(c)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(d)

Figure 14 Continued




1 + e(60+15 Dminus GSI11)1113888 1113889 (2)




0

2

4

6

8

10

12

14

16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


0

2

4

6

8

10

12

14

16

18

20

Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)





06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References
































(a) (b) (c) (d) (e)



0

2

4

6

8

10

12

14

Rdat

ions

of c

ircul

ar d

egre

e C


(a)


0

5

10

15

20

25

Rdat

ions

of c

ircul

ar d

egre

e C


(b)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(c)


0

2

4

6

8

10

12

14

16

Rdat

ions

of c

ircul

ar d

egre

e C


(d)

Figure 14 Continued




1 + e(60+15 Dminus GSI11)1113888 1113889 (2)




0

2

4

6

8

10

12

14

16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


0

2

4

6

8

10

12

14

16

18

20

Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)





06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References


































1 + e(60+15 Dminus GSI11)1113888 1113889 (2)




0

2

4

6

8

10

12

14

16Rd

atio

ns o

f circ

ular

deg

ree C


(e)


0

2

4

6

8

10

12

14

16

18

20

Rdat

ions

of c

ircul

ar d

egre

e C


(f)


0

2

4

6

8

10

12

14

16

18

Rdat

ions

of c

ircul

ar d

egre

e C


(g)





06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References


































06leσH

σV

le1550

H+ 06 (3)

k 1903

H+ 10399 (4)









Z

Y

X

ZX

200m

300m

600m







16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References




































16

σzzσxx

21

22St

ress

(MPa

)


(a)

σzzσxx


16

18

20

22

24

26

28

Stre

ss (M

Pa)

(b)



Interface(elements)

Piece 2

Piece 12D 3D

R

xc

go

x(2)

x(1)

(a)


Core Skirted face

Faced grain(rigid)

(b)



























(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References
























































(a)

0

20

40

60

80

100


Stre

ss (M

Pa)


Strain

(b)


σzz

σxx σxx 45m

62m


25

25

15

15

5

5

ndash5

ndash5

ndash15

ndash15ndash25

ndash25

121R (m)

10171510



6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References
































6 Conclusions






7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c) (d)

(e) (f )


7

3

ndash1

ndash5

ndash6 ndash2 2 6

(a) (b) (c)






Data Availability




Acknowledgments


References



































Data Availability




Acknowledgments


References
































fracturingofthesoftrocksurroundingaroadwaysubjectedto … · 2020. 8. 25. ·...

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