RuptureandMigrationLawofDisturbedOverburdenduring ...downloads.hindawi.com/journals/ace/2020/8863547.pdf · 2020. 10. 8. · ResearchArticle RuptureandMigrationLawofDisturbedOverburdenduring

Research ArticleRupture and Migration Law of Disturbed Overburden duringSlicing Mining of Steeply Dipping Thick Coal Seam

Shuai Liu 123 Ke Yang 23 Chunan Tang 14 and Xiaolou Chi 23

1School of Resources and Civil Engineering Northeastern University Shenyang 110819 China2Institute of Energy Hefei Comprehensive National Science Center Hefei 230031 China3State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal MinesAnhui University of Science and Technology Huainan 232001 China4School of Civil and Hydraulic Engineering Dalian University of Technology Dalian 116024 China

Correspondence should be addressed to Ke Yang keyang2003163com

Received 27 August 2020 Revised 13 September 2020 Accepted 23 September 2020 Published 8 October 2020

Academic Editor QiFeng Guo

Copyright copy 2020 Shuai Liu et al +is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Steeply inclined and thick coal seams in Huainan Panbei Coal Mine in Anhui Province China were analyzed by physical analogmodeling acoustic emission (AE) and distributed fiber sensing (DBS)+e secondary deformation breakage law sound and lightresponse characteristics in the rock mass deformation process induced by lower slice mining of steeply inclined coal seams weredetermined +e results show that the mutation of the hinged rock beam structure in the lower region and the cantilever beamstructure in the upper region of the lower slice disturbed overburden is the main cause of the rupture of the workface roof Basedon the AE energy and distributed fiber strain response characteristics the six stages of disturbed overburden instability in thelower slice and cyclic patterns of steeply inclined coal seams were revealed +e key prevention and control areas of the workfacewere found to be related to the disturbed high-level immediate roof rupture during the lower slice mining process rupture of thedisturbed main roof and sliding of disturbed overburden+e three-stage AE positioning morphological characteristics and DBSresponse stepped jump patterns were analyzed in detail +e research results are considered instrumental in the combined AE andDBS monitoring of deformation and damage of rock and soil structures

1 Introduction

Coal seam mining causes overburden movements whichcan jeopardize coal production safety +erefore min-ing-caused overburden movement patterns are vital formining technology [1] However due to the high cost offield research limitations of monitoring equipment andother factors the overburden deformation and rupturelaws are mainly determined by the physical analogmodeling (PAM) +is is a robust laboratory techniquefor reproducing at small scale geometric and kinematicfeatures of natural geologic structures by a proper se-lection of deformation styles and analog materials +elatter include sand claycake silicon putty and so forthand simulate rock strata table-top scale analog layersUnder the condition of satisfying the basic similarity

principle PAM can accurately reflect the engineeringstructure relationship Because of its unique superiorityit is widely used in geotechnical engineering [2 3] Manyscholars have used PAM to analyze the gangue slip fillingcharacteristics after rupture of steeply inclined coalseams overburden +ey studied the dip and antidipdirectionsrsquo pile structure in the process of steeply in-clined coal seams workface gangue slip obtainedasymmetric ldquoruptured archrdquo of steeply inclined coalseams overburden and revealed the asymmetric ldquoarchshellrdquo form of overburden space mining by steeply in-clined coal seams [4 5 6 7 8 9] However due to thecoal seam occurrence conditions and mining technologyimpacts in steeply inclined and thick coal seams slicedmining the overburden structure changes under theinfluence of multiple mining Given this the laws of

HindawiAdvances in Civil EngineeringVolume 2020 Article ID 8863547 11 pageshttpsdoiorg10115520208863547

disturbed overburden rupture and migration afteroverburden structural change in steeply inclined coalseams mining are very topical

+e PAM approach envisages deformation monitoringvia total stations dial gauges strain gauges and so forthwhose testing accuracy and sensitivity need further im-provement most of them use point monitoring while thelayout of points and lines is too complicated In generaldeformation monitoring can only monitor the modelrsquossurface but fail to implement internal monitoring With therapid development of acoustic emission (AE) nondestructivedetection technology numerous researchers had success-fully used it to detect the number of events and energy ratesof the PAM when the chasm slips were unstable [10] +eyobtained the precursor information of chasm instability andrevealed the characteristics and dynamic response laws ofstope pressure before and after the activation of chasms [11]Besides the AE technology was also utilized in the assess-ment of characteristics of the spatial-temporal evolution ofdynamic instability of large-inclination coal and rock masses[12 13 14 15 16] Another hot field of research is fibersensing technology which can achieve long-distance dis-tributed monitoring Using the advantages of anticorrosionantielectromagnetic interference small size lightweighthigh sensitivity high precision and so forth it ensures thestability monitoring for geotechnical [17 18] geology[19 20] water conservation [21] aerospace [22] defense[23] and other applications References [24ndash26] incorpo-rated the optical fiber sensing technology into the logicalphysical model to monitor the deformation and weighting ofworkface overburden which yielded interesting findings+is technology has been successfully applied to the mon-itoring of overburden migration in coal mine goaf [27 28]

In this study the PAM AE and distributed fibersensing (DBS) are jointly applied to steeply inclined coalseams for assessing the disturbed overburden secondarydeformation and rupture patterns as well as the char-acteristics of sound and light response in the process ofrock deformation and rupture +is research can provide atheoretical reference for the prevention of hazards such asrib spalling roof falling and support instability +eresearch results are considered instrumental in the AE andDBS detection of rock and soil structure deformation anddamage

2 Principles of Acoustic and OpticalDetection Methods

21 AE-Based Positioning by Time Differences Positioningby time differences is aimed to determine the soundsourcersquos coordinates or position by measuring the pa-rameters of each AE channel signal TDOA wave speedand sensor spacing and their processing via a certainalgorithm +is accurate yet complicated positioningmethod has been widely applied in component detectionsWhen performing planar positioning on a diamond arraycomposed of four AE sensors AE can obtain a real po-sitioning sound source as shown in Figure 1 In actualcomponent AE monitoring the number of AE sensors

often exceeds four If an individual AE sensor fails duringmonitoring the remaining four AE sensors can stillmonitor a real positioning sound source

Assume that the hyperbolic curve 1 is obtained from thetime difference ΔtX between S1 and S3 AE sensors thehyperbolic curve 2 is obtained from the time difference ΔtYbetween S2 and S4 AE sensors the positioning sound sourceis Q the distance between S1 and S3 sensors is a the distancebetween S2 and S4 sensors is b and the wave velocity is V+en the positioning sound source is located at the inter-section point Q (X Y) of the two hyperbolae and its co-ordinates can be expressed as follows

X ΔtXV

2aLX + 2

X minusa

21113874 1113875

2+ Y

2

1113971

⎡⎢⎢⎣ ⎤⎥⎥⎦

Y ΔtYV

2bLY + 2

Y minusb

21113888 1113889

2

+ X2

11139741113972

⎡⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎣

⎤⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎦

(1)

22 Optical Fiber Sensing Measurements DBS uses opticalfibers as sensing elements When the measured fiber issubjected to an external force or temperature variations thefrequency of the stimulated Brillouin scattered light in thefiber will change +e strain data transferred along the fibercan be obtained by conversion +e relationship between theBrillouin frequency shift temperature and strain is [29]

Δε ΔVB minus C1ΔT( 1113857

C2 (2)

where ΔVB is Brillouin frequency shift MHz C1 is tem-perature sensitivity coefficient MHzdegC C2 is strain sensi-tivity coefficient MHzμε ΔT is temperature variation degCand Δε is strain variation +is method is based on theprinciple of light scattering and measures the frequencychange of Brillouin scattered light

It is generally believed that when the temperature var-iation is within 5degC the Brillouin frequency shift caused bythe temperature can be ignored In this study this test is

X

Y

Q(X Y)

12

S4

S1

S2

S3

a

b

Figure 1 +e AE sound source positioning of an array composedof four AE sensors

2 Advances in Civil Engineering

carried out indoors and the measured temperature variationis less than 3degC +erefore the temperature effect on themeasurement results can be ignored

3 Physical Analog Modeling Procedure

31 Case Study +e experiment uses 12123 working face ofthe Huainan Panbei Coal Mine in Anhui Province China asthe engineering geological case study +e main coal seam is13ndash1 coal seam the average seam inclination angle is 40degthe average thickness is 44m and inclined mining in slicesis adopted+e upper slice has a mining height of 20m and asurface length of 120m Recovery was completed in 2015+e lower slice has a mining height of 24m and a surfacelength of 90m +e recovery interval between the upper andlower slices is two years +e lower slice is arranged in themiddle and lower parts of the goaf in the upper sliceSpecifically the lower slicersquos gate road is 50m away from thegate road in the upper slice Figure 2 is a schematic diagramof the location and production conditions of 12123 workingface +e coal seam hardness coefficient (f ) is 03sim05 theimmediate roof is the interslice of mudstone and sandymudstone and the average thickness is 93m+e immediatefloor is mudstone and the average thickness is 30m

32 Physical Analog Model (PAM) +e test uses a rotatingplane PAM frame the device dimensions arelengthtimeswidthtimes height 20mtimes 02mtimes 20m PAM re-quires that each partrsquos size is enlarged or reduced accordingto a uniform ratio between the physical model and theprototype which is lmlp Cl According to the 12123working face engineering geological data and test devicedimensions we determined the geometric similarity con-stant lmlp Cl 100 bulk density similarity constantCc cpcm 16 stress similarity constant Cc Cc Cl 160and time similarity constant Cτ Cl

12 10 In the abovesimilar constant formulas the subscript parameters p andmrepresent the prototype and model respectively

+e test uses river sand as aggregate gypsum lime ascementing material and water as the bonding material Dueto the articlersquos limited space the detailed similar materialratio and modeling process are omitted and can be foundelsewhere [30 31] Based on the similarity constant and thephysical and mechanical parameters of coal the weightedmixing test between the above analog materials was used toadjust and determine the similarity ratio and then calculatethe proportions of analog materials in each coal slice Analogmaterials are also stirred laid and compacted slice by sliceDifferent colors are sprayed on different rock slices of thehigh-level floor of the workface to distinguish them +ephysical and mechanical parameters of coal and similarmaterials are listed in Table 1

+e test laying height is 15m and the workface burialdepth ranges from minus375 to minus495m After the overlyingnonsimulated rock slice is converted by a load similarconstant the top of the physical model is loaded by amultifunctional adjustable PAM loading device +e com-plete physical model is depicted in Figure 3

33Monitoring System Coal pillars of 50 cm are left on eachside of the upper slice+e upper and lower simulation slicesrsquoexcavation distance is 10 cm the upper slice is excavated 12times and the lower one is excavated nine times each ex-cavation duration is about 1min +e interval of each ex-cavation is 20min

Steeply inclined coal seams are generally cut from top tobottom and the frame is moved from bottom to top Whenthe rock slice is broken the slippage mainly occurs duringthe frameshift phase+erefore the bottom-up simulation ofcoal cutting is adopted in the two-dimensional physicalmodel Six AE sensors numbered P1ndashP6 are embeddedbeforehand in the physical model to facilitate the picking of3D positioning points Among them P1 P3 and P5 areembedded in the front while P2 P4 and P6 are implanted inthe back+e specific locations are shown in Figure 4 Beforethe workface simulation recovery the AE parameters needto be calibrated and the upper slice recovery process is usedto check the accuracy of the AE parameters +e AE sensorrsquosresonance frequency is finally determined to be100ndash600 kHz the sampling rate is 3MHz the preamplifiergain is 40 dB and the monitoring threshold is 90 dB Withsuch AE parameters the AE signal is not affected by theexcavation action which is convenient for later datascreening When the lower slice is excavated the AE isturned on synchronously until the overburden structure isstable

+e distributed fiber uses a high-transmission low-rigidityresponsive sensing optical cable with a 2mm diameter andthe fiber placement is shown in Figure 4 +e optical fiber isembedded in analog materials To make the optical fiber tighta certain pretightening force is applied to both optical fiberends A small amount of cement slurry is put tomake it tightlycoupled with analogmaterials Like AE parameter calibrationoptical fiber also needs to be calibrated for strain coefficientaccuracy For brevity sake a detailed calibration process canbe found elsewhere [32] +e spatial resolution of the opticalfiber strainmeasurement is set to 50mm+e optical fiber canmonitor the rock slicersquos deformation and rupture before andafter the overburden structure disturbance in the upper andlower slices on a real-time scale +e optical fiber strainrsquospositive and negative values indicate that the analog materialis in a stretched and compressed states respectively +ephysical model is installed in front of the camera to monitorthe rock deformation and rupture

4 Results and Discussion

41 Rock Slice Rupture and Migration Features After theupper slice excavation the immediate roof breaks at theheight of 93m and the gangue moves down along the floorof the workface +e ganguersquos nonuniform filling charac-teristics are enhanced showing the goaf filling with anldquoupper empty middle full and down solidrdquo feature +eimmediate high-level roof has a macrofracture (crack line inA-A red frame) and the rock slice below the fracture surfaceloses its bearing capacity In contrast a stable cantileverbeam structure (A-A red frame) is formed above the fracturesurface which has a certain bearing capacity In the workface

Advances in Civil Engineering 3

lower area the gangue piles up the overburdenrsquos movementspace in the mined-out area decreased and overburdenshows transverse and longitudinal cracks and delamination[33 34] It is still not completely separated from the stablerock slice and has the form of a hinged rock beam structure

Its load directly acts on gangue (or bracket) According tothe time similarity constant after the upper slice overburdenis stabilized continue to excavate the lower slice as shown inFigure 5 After the lower slicersquos excavation there is a freespace height below the disturbed overburden and the

Table 1 Rock physical and mechanical parameters and similarity ratios

Rockproperty

Compressivestrength (MPa)

Elasticmodulus(GPa)

Cohesion(MPa)

Internalfriction angle

(deg)

Poissonrsquosratio

Similarityratio

Mass (kg)Fineriversand

Lime Gypsum Water

Mediumsandstone 5786 1800 241 35 020 6 6 4 3512 351 234 410

Finesandstone 7008 1532 268 38 015 6 6 4 3448 345 230 402

Sandymudstone 3563 951 122 30 028 7 7 3 4770 477 204 545

Mudstone 2152 624 095 24 030 10 7 3 1423 100 042 15613ndash1coal 1346 583 062 20 035 10 5 5 3510 176 176 386Mudstone 2152 624 095 24 030 10 7 3 1627 114 049 179Sandymudstone 3563 951 122 30 028 7 7 3 2915 292 125 333

Main roof

High-levelimmediate roof

Low-levelimmediate roof

13-1 coal seam

Immediate floor

Multifunction adjustablephysical simulation

loading device

960620230050760090040600720680250440300460220650

Sandy mudstone

Fine sandstone15-1 coal seamSandy mudstoneSiltstone14-1 coal seamMedium sandstoneFine sandstone

Fine sandstone

Sandy mudstone

Sandy mudstone

Sandy mudstone

Siltstone

Siltstone13-1 coal seam

Siltstone

Figure 3 Physical analog model

N24m

China

Anhui province

Study area (Panbei Mine)

25m

90m 120m

2m

13 coal

5m

Tailentry

Headentry 40deg

Upp

er sl

ice

Botto

m sl

ice

Cata

clasti

c reg

ener

ated

roof

Figure 2 +e location and production conditions of 12123 working face


ganguersquos ability to restrain the disturbed overburden isweakened Under the superposition of overburden gravityand mining stress the hinged rock beam formed by dis-turbed overburden breaks and slips after ldquoactivationrdquo +edisturbed overburden structure is changed

Specifically the overlying low-level disturbed overbur-den (BndashBmiddle and lower parts sprayed with red and darkgreen) emerges during mining which exposes the high-leveldisturbed overburden above it Gangue slides along theworkface floor to fill the lower part of the goaf while the freespace below the disturbed overburden in the middle andupper parts of the goaf (available for the rock slice to breakand rotate) increases+e disturbed overburden breaks up tothe main roof (Bprime-Bprime part sprayed with dark blue paint) +ebreaking height is 165m After the simulated excavationreaches the upper end of the lower slice the structure of thecantilever beam formed after the upper slice excavation isunstable and together with the disturbed overburden abovethe coal pillar has slip damage without any support (Aprime-Aprimered frame) with the development of coal pillar cracks andsevere gangling (Aprime-Aprime yellow frame)

Comprehensive analysis shows that during the lower slicerecovery process the disturbed overburden is severely brokenunder the secondarymining action and it is very easy to inducethe roof collapse which causes the bracket to be improperlyconnected and the bracket falls slips reverses and becomesunstable For the lower slice return airway the first requiredmeasure is to prevent the roof from breaking and the secondone is to avoid the breaking impact of the cantilever beamformed by the high immediate roof above the coal pillar on thesupport after the upper slice recovery

42 Rock Slice Rupture AE Response +e physical analogmodel has a large scale and the distance between the AEsensors is relatively large According to a single AE sensor itis difficult to obtain the AE response law of distorted

overburden deformation and rupture Hence based on thetime node after disturbed overburden structure mutation oflower slice mining the data of six AE sensors are synthesizedto extract the parameters such as energy and ring count andare recorded as the number of one event+e 3D positioning(AE events) in the gangue sliding process is relativelyrandom Only the 3D positioning AE data of the disturbancecaused by high roof breaking rupture of the disturbed mainroof and sliding of disturbed overburden are extractedEnergy is a relative value monitored by the AE analyzer perunit time and is an important indicator of the fracture rateand size of the rock mass the ring count is the cumulativevalue monitored by the AE analyzer per unit time and is animportant indicator of the rock mass destruction

Figure 6 depicts the relationship between the break andslip of the lower slice disturbed overburden and timeDuring the lower slice recovery process primary cracks inthe disturbed overburden continue to develop a largeamount of elastic energy accumulating at the crack tip andits surroundings

+e AE energy gives rise to six higher-energy bundles+e first energy peak of the AE multimodal energybundle is the largest +en the peak value graduallydecreases within the duration of each disturbed over-burden break or it appears as a single peak It shows thatthe instability of the lower slice disturbed overburden hasgone through six stages and when the disturbed over-burden breaks in each stage the first break strength is thelargest +e first energy bundle appears when the dis-turbed low-level immediate roof (BndashB part painted in redin Figure 5) is broken +e elastic wave released by thebroken overburden at this stage is low and its duration isshorter +e peak value of AE energy is 7783 mVmiddotmS andthe cumulative ring count increases slowly +e secondenergy bundle appears when the disturbed high-levelimmediate roof (BndashB part painted in dark green partFigure 5) is broken At this stage the peak value of AE

40 DS5-16B multichannel full-wave AE signal

analyzer

FTB2505 distributedoptical fiber analyzer

AE sensors

Upper and lower slice

Optical fiber Units cm

10

50 p1

p2

p3

p4

p5

p6

Figure 4 Monitoring system


energy shows a ldquogroup shockrdquo phenomenon +e highestpeak value reaches 49731 mVmiddotmS the duration is 38 sthe cumulative ring count jumps from 2867 to 3631 andthe total number of events in this stage is 2462 n +ethird energy bundle appears when the gangue slidesalong the workface floor after the disturbed high-levelimmediate roof is broken +e lower slicersquos gangue isstacked the free space height in the middle and upperregions increases and the exposed length of the dis-turbed main roof increases +e fourth energy bundleappears when the exposed disturbed main roof (BBsprayed blue part in Figure 5) breaks At this stage thepeak value of AE energy is ldquoisolatedrdquo +e isolated peakvalue of AE is 39143 mVmiddotmS +e duration is 3s the

cumulative ring count jumps rapidly from 4541 to 5574and the total number of events at this stage is 726 n +isshows that the rock breakage at this stage is ldquoabruptrdquo

After the rock slices at the first and second stages arebroken gangue has filled the lower and middle parts of thelower slice +e space available for gangue slippage after thefourth stage rupture of the disturbed main roof is reducedthat is the fifth energy bundle caused by gangue slippage isweak and exhibits a ldquosolitary shockrdquo formWhen the upwardsimulation excavation reaches the upper part of the lowerslice the disturbed overburden above the coal pillar breaksand slips under the joint action of overburden load andmining stress +e sixth energy bundle emerges +e highestenergy peak is 38015mVmiddotmS the duration is 11 s the

A-A

A-A

Arsquo-Arsquo

B-B

B-B

Brsquo-Brsquo

Upper part ofupper slice

Overburden structure changes

Transverse and

longitudinal cracks

Gangue slidebackfilling

Bed separation

Rib spalling

Lower part ofupper slice


Upper part oflower slice

Lower part oflower slice

Figure 5 Workface overburden structure variation stages


cumulative ring count jumps from 5854 to 7270 and thetotal number of events is 2084 n

+e procedure requires breaking the disturbed high-levelimmediate roof importing the 3D positioning AE data of therupture of the disturbed main roof and sliding the disturbedoverburden into AutoCAD software to generate 3D posi-tioning line drawings and perform postprocessing such ascoloring Figure 7 shows the spatial positioning pattern ofthe generated disturbed overburden breaking AE signals Asobserved the distribution of AE spatial positioning points isroughly corresponding to the broken position of the dis-turbed overburden (Aprime-Aprime Bprime-Bprime red box in Figure 5) in thelower slice Disturbed high-level immediate roof breaking offlocations of AE in the space are more scattered mainlyextending from the location of the disturbed high-levelimmediate roof to the surrounding area showing the relativeductility destruction of the disturbed high-level immediateroof rock slice Rupture of disturbed main roof AE posi-tioning points is concentrated in space showing the relativebrittleness damage of disturbed main roof After simulatingthe excavation of the lower slicersquos upper area disturbedoverburden damage and slips the AE space positioningpoints are distributed in a ldquoflow-likerdquo way

+e comprehensive analysis revealed that macro- andmicrocracks in the disturbed high-level roof were moredeveloped Under the superimposed action of overburdenload and mining stress macro- and microcracks continuedto store elastic energy When the energy storage limit wasreached the disturbed high-level immediate roof breakinglasted for a long time and the energy released was quite high(the second energy bundle) However the amount of energyreleased per unit time was relatively small +e internalcracks in the rock slice had sufficient time to evolve anddevelop +e distribution of 3D positioning points was di-vergent and the damage degree of the rock body was in-creased +e rock body was broken and the broken ganguemoved violently in the lower slice goaf (or support top

beam) Disturbed main roof macro- and microcracks werenot developed Under the superimposed action of over-burden load and mining stress the macro- and microcracksreleased higher energy after reaching the energy storage limitin a short time (the fourth energy bundle) +e cumulativeringing count per unit time exhibited a sharp jump and therock mass was quickly fractured +e internal structure ofthe rock slice had no time to evolve and was damaged +edistribution of 3D positioning points was aggregated andthe overall damage degree of the rock body was small +edisturbed main roof possessed the characteristics of suddendamage and could produce the impact-caused instability tothe lower sliced support When the simulated excavationreached the lower slicersquos upper part the disturbed over-burden slips but its integrity after fracture was high +edistribution of 3D positioning points was streamlined +ecumulative value of the ringing count in the disturbedoverburden slipping process per unit time was between thevalue of disturbed high-level immediate roof process and thevalue of rupture of disturbed main roof process

43 Rock Rupture Fiber Response +e first mining of theupper slice (advance of 10 m) is detected by optical fibersensing indicating that the fiber senses the weak defor-mation inside the rock slice As shown in Figure 8(a) whenthe upper slice excavation is simulated the fiber responseshows a ldquodouble peakrdquo shape and peak sizes are 436 and534 με respectively +e corresponding physical modelheights are 680 and 980mm respectively +e fiber responsedouble peak position is projected onto the upper sliceworkface which is mainly located in the middle and upperregions of the upper slice After the steeply inclined coalseams mining the overburden in the upper part of theworkface breaks and slips +e gangue fills the lower part ofthe workface hindering the continued breakage of theoverburden in the lower part of the workface +ere is a high

Abrupt change

Abrupt change

Abrupt change

0

1

2

3

4

5

AE

ener

gy (1

03 mV

mS)

Disturbedhigh-level

immediate roofbreaks

0

1

2

3

4

5

6

7

AE

even

t cou

nt (1

02 n)

0

1

2

3

4

5

6

7

8

Cum

ulat

ive A

E co

unt (

103 )

Firstenergypeak

Secondenergypeak

Thirdenergypeak

Fourthenergypeak

Fifthenergypeak

Sixthenergypeak

Disturbedmain roof

breaksDisturbed

overburdenslips

200 400 600 800 10000Duration (s)

Figure 6 Relationship between disturbed overburden breaking and slipping AE parameters and time


peak fiber response in the upper part of the workface and asmall peak response in the lower part further explaining theasymmetric feature of steeply inclined coal seams workfaceoverburden breakage

Taking the fiber response before and after the disturbedhigh-level immediate roof breakage as an example theoptical fiber response change characteristics before and afterthe lower slice disturbed overburden breakage are analyzedand the results are shown in Figure 8(b) As observed beforethe lower slice disturbed high-level immediate roof breaksthe tensile stress concentration occurs in the disturbedoverburden (the fiber response value is positive) and theelastic deformation in the rock gradually accumulates +epeak value of the optical fiber response is 2095 με and thepeak position is located above the breaking line of thedisturbed high-level immediate roof while the height of thecorresponding physical model is 673mm After an imme-diate high-level roof of the disturbed lower slice is brokenthe rock mass in the fiber-implanted slice shows a certaindegree of stress release and the accumulated elastic strainenergy is also released +e optical fiber responsersquos peakvalue drops from 2095 to 1717 με and the peak position isthe same as before the disturbed high-level immediate roofbreakage +is is consistent with AErsquos response law beforeand after the breakage of the disturbed high-level immediate

roof (the AE energy accumulation in the rock before thebreakage and the release of AE energy after the breakage)For the rupture of the disturbed main roof and disturbedoverburden the fiber response before and after the slip alsofollows the same pattern (more detailed analysis is omittedfor brevity) +e critical point on the optical fiber responsecurve in the whole process of the lower slice simulationexcavation from monotonous increase to monotonous de-crease is roof breaking +e instantaneous response beforebreaking reaches the maximum value After breaking theroof rock slice quickly releases pressure and stress istransferred to the deep stable rock mass around the goaf Atthis time the roof rock slicersquos stress at the breaking positionreaches the minimum value and the overburden movementgradually stabilizes After that as the work surface advancesit monotonically increases again and the process forms thework surface with a periodic mineral pressure trend +ecycling process forms the appearance of the workfacersquosperiodic mineral pressure along the inclined workface

During the lower slice simulation excavation theoptical fiber response data after the disturbed high-levelimmediate roof rupture rupture of the disturbed mainroof and disturbed overburden slipping are extracted asshown in Figure 8(c) As observed after the rupture of thedisturbed high-level immediate roof the rock slice is

20

140

120

100

80

60

40

20

0

Phys

ical

mod

el h

eigh

t (cm

)

20 40 60 80 100 120 140 160Physical model length (cm)

Disturbed overburden

slipsUpper and lower slice

Disturbed maim roof

breaks

Disturbed high-level

immediate roof breaks

Figure 7 Disturbed overburden rupture AE spatial positioning pattern


opened to form a separation crack which causes thetensile stress concentration in the optical fiber With theupward excavation of the PAM and the rupture of thedisturbed main roof the optical fiber responsersquos peakvalue jumps from 1717 to 2547 με in steps +e peakposition is located above the line of the rupture of thedisturbed main roof +e specific height of the corre-sponding PAM is 796mm With the simulated excavationof the lower slicersquos upper area the optical fiber senses thedisturbed overburden slip in the upper area of the lowerslice and the peak value of the optical fiber strain also

shows a stepped jump of 1575 με +e peak positioncorresponds to the PAM height of 1078mm +e dis-tributed fibers monitor the process of abscissa slice de-velopment expansion closure rebirth and so forth +eabscissa slice development length gradually expands asthe lower slice progresses upward along the inclination

+e sandstone in the upper part of the lower slice (Aprime-Aprimeand Bprime-Bprime sprayed green part in Figure 5) does not changesignificantly in the subsequent excavation process indi-cating that the upper part sandstone constitutes themain keyslice of the physical model

1500

1200

900

600

ndash500 ndash1500 0 500 1500 2500

300

0

Phys

ical

mod

el h

eigh

t (m

m)

Strain (με)

Optical fiber

Optical fiberresponse

Upper sliceadvance 10cm

Upper slice advance 10cmUpper slice advance completed

(a)

1500

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)

Before the disturbed high-level immediate roof breaksAfter the disturbed high-level immediate roof breaks

Disturbed high-levelimmediate roof breaks

Optical fiber

(b)

1500 Optical fiber

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)

Disturbedoverburden slips

Disturbed main roofbreaks


Disturbed high-level immediate roof breaksDisturbed maim roof breaksDisturbed overburden slips

(c)

Figure 8 Roof fall fiber response characteristics (a) Upper slice recovery fiber response (b) disturbed high-level immediate roof rupturefiber response and (c) rock rupture in the lower strata in different regions of fiber response


44 Substantiation ofgtree Key Protection Areas in the LowerSlice by Fiber Sensing and AE Methods +e AE and dis-tributed fiber monitoring results inevitably have errorsPAM has a plane stress state from an experimental per-spective and constraints do not effectively control its sur-face +e brittle sand material affects the contact area of thesensor and the effective transmission of strain data From theperspective of AE and fiber sensing technology the brokenrock slice leads to incomplete contact between the sensorand rock slice causing slippage and shedding All thesefactors may bring uncertainty to themeasurement Althoughdifferent sound and light measurement methods have cer-tain differences in specific values the overall regularity is notchanged It is necessary to analyze the influencing factors infurther research and eliminate them gradually

Under the influence of secondary mining the lower slicedisturbed overburden slips and the lower slicersquos returnairway is seriously damaged +e disturbed main roof in thecentral area of the workface breaks ldquosuddenlyrdquo which has apositive impact on the bracket and may cause the bracket tofall slip and become unstable +e disturbed high-levelimmediate roof in the lower area of the workface breaks thegangue slides down along the floor of the workface and theworkface undergoes such disasters such as roof collapse Tocontrol the mining systemrsquos stability in different regions theso-called ldquotriunity collaborative support systemrdquo is proposedfor the protection of roadway sides workface roof andsupport brackets +e above support system implementationin the three key protection areas of the lower slice will makeit possible to avoid the workfacersquos large-scale roof collapseside falling bracket instability or other violation of theworkface mining safety Engineering practice has verified thefeasibility of the proposed subdivision of the three keyprotection areas in the lower slice

5 Conclusions

+e physical analog modeling of the particular case study(the Huainan Panbei Coal Mine in Anhui Province China)was used to derive the rupture characteristics and migrationof the disturbed overburden in steeply inclined coal seams+e joint application of AE and fiber response techniquesmade it possible to draw the following conclusions

(1) +e secondary mining results in breakage and slip ofthe disturbed overburden hinged rock beam in thelower area and the cantilever beam in the upper area+e overburden structure is mutated which causesthe lower slice roof to break and it is easy to inducethe workface roof collapse side falling instabilityand so forth

(2) +e lower slicersquos disturbed overburden experiencessix stages of damage and instability and at each stageof the broken overburden the AE energy bundle ismultimodal +e first energy peak in the AE mul-timodal energy bundle is the largest

(3) +e optical fiber can sense a small-scale deformationof the rock mass +e critical point where the opticalfiber response develops frommonotonous increasing

to decreasing is roof breaking +e instantaneousstrain before breaking attains its maximum valueand the overburden reaches stability when the stressis released to a minimum value After that as theworkface advances it is again monotonically in-creasing +e cycling process creates periodic pres-sure fluctuations along the inclined workface

(4) During the lower slicersquos mining process three keyprevention and control areas namely the disturbedhigh-level immediate roof rupture rupture of thedisturbed main roof and sliding of disturbedoverburden are observed +e AE energy per unittime in the three phases is higher than that in otherbreaking phases and the rock mass fracture rate ishigher while the fiber sensing exhibits a suddenchange in response value and a stepped jump in-crease +e research results are considered instru-mental in the application of acoustic emission andfiber sensing to the deformation and damagemonitoring of rock and soil structures

Data Availability

+e data used for conducting classifications are availablefrom the corresponding author upon request

Conflicts of Interest

+e authors declared no potential conflicts of interest withrespect to the research authorship andor publication ofthis article

Acknowledgments

+is work was supported by the National Natural ScienceFoundation of China (no 51634007) and the Institute ofEnergy Hefei Comprehensive National Science Centerunder Grant no 19KZS203

References

[1] M G Qian and J L Xu ldquoBehaviors of strata movement in coalminingrdquo Journal of China Coal Society vol 44 no 4pp 973ndash984 2019 in Chinese

[2] C O Aksoy H Kose T Onargan Y Koca and K HeasleyldquoEstimation of limit angle using laminated displacementdiscontinuity analysis in the soma coal field western TurkeyrdquoInternational Journal of Rock Mechanics and Mining Sciencesvol 41 no 4 pp 547ndash556 2004

[3] M Z Gao ldquoSimilarity model test of strata movement withsteep seamrdquo Chinese Journal of Rock Mechanics and Engi-neering vol 23 no 3 pp 441ndash445 2004 in Chinese

[4] X Chi K Yang and Q Fu ldquoAnalysis of regenerated roof andinstability support control countermeasures in a steeplydipping working facerdquo Energy Exploration amp Exploitationvol 38 no 4 p 1082 2019

[5] J Liu S L Chen H J Wang Y C Li and X W Geng ldquo+emigration law of overlay rock and coal in deeply inclined coalseam with fully mechanized top coal cavingrdquo Journal ofEnvironmental Biology vol 36 no 4 pp 821ndash827 2015


[6] W Lv Y Wu L Ming and J Yin ldquoMigration law of the roofof a composited backfilling longwall face in a steeply dippingcoal seamrdquo Minerals vol 9 no 3 p 188 2019

[7] H S Tu S H Tu C Zhang L Zhang and X G ZhangldquoCharacteristics of the roof behaviors and mine pressuremanifestations during the mining of steep coal seamrdquo Ar-chives of Mining Sciences vol 62 no 4 pp 871ndash891 2017

[8] Y P Wu P S Xie and S G Ren ldquoAnalysis of asymmetricstructure around coal face of steeply dipping seam miningrdquoJournal of China Coal Society vol 35 no 2 pp 182ndash184 2010in Chinese

[9] P S Xie S Q Tian and J J Duan ldquoExperimental study on themovement law of roof in pitching oblique mining area ofsteeply dipping seamrdquo Journal of China Coal Society vol 44no 10 pp 2974ndash2982 2019 in Chinese

[10] Q Guo J Pan M Cai and Y Zhang ldquoInvestigating the effectof rock bridge on the stability of locked section slopes by thedirect shear test and acoustic emission techniquerdquo Sensorsvol 20 no 3 p 638 2020

[11] Q Guo J Pan M Cai and Y Zhang ldquoAnalysis of progressivefailure mechanism of rock slope with locked section based onenergy theoryrdquo Energies vol 13 no 5 p 1128 2020

[12] X P Lai H Sun P F Shan C L Wang N Cui andY R Yang ldquoAcoustic emission and temperature variation infailure process of hard rock pillars sandwiched between thickcoal seams extremely steeprdquo Chinese Journal of Rock Me-chanics and Engineering vol 34 no 11 pp 2285ndash2292 2015in Chinese

[13] X P Lai Y R Yang N B Wang P F Shan and D F ZhangldquoComprehensive analysis to temporal-spatial variation ofdynamic instability of steeply inclined coal-rock massrdquoChinese Journal of Rock Mechanics and Engineering vol 37no 3 pp 583ndash592 2018 in Chinese

[14] H W Wang M M Shao G Wang and D X DengldquoCharacteristics of stress evolution on the thrust fault planeduring the coal miningrdquo Journal of China Coal Society vol 44no 8 pp 2318ndash2327 2019 in Chinese

[15] K Yang X L Chi Q J LiuW J Liu and S Liu ldquoResearch oncataclastic regenerated roof and instability mechanism ofsupport in fully mechanized mining face of steeply dippingseamrdquo Journal of China Coal Society vol 20 pp 1ndash10 2020 inChinese

[16] S K Zhao ldquoExperiments on the characteristics of thrust faultactivation influenced by mining operationrdquo Journal of Miningand Safety Engineering vol 33 no 2 pp 354ndash360 2016 inChinese

[17] L J Butler N Gibbons P He C Middleton andM Z E B Elshafie ldquoEvaluating the early-age behaviour offull-scale prestressed concrete beams using distributed anddiscrete fibre optic sensorsrdquo Construction and Building Ma-terials vol 126 pp 894ndash912 2016

[18] A Klar I Dromy and R Linker ldquoMonitoring tunnelinginduced ground displacements using distributed fiber-opticsensingrdquo Tunnelling and Underground Space Technologyvol 40 no 2 pp 141ndash150 2014

[19] X Jiang Y Gao Y Wu and M Lei ldquoUse of brillouin opticaltime domain reflectometry to monitor soil-cave and sinkholeformationrdquo Environmental Earth Sciences vol 75 no 3pp 1ndash8 2016

[20] H-H Zhu B Shi J-F Yan J Zhang and J Wang ldquoIn-vestigation of the evolutionary process of a reinforced modelslope using a fiber-optic monitoring networkrdquo EngineeringGeology vol 186 pp 34ndash43 2015

[21] M Kihara K Hiramatsu M Shima and S Ikeda ldquoDistrib-uted optical fiber strain sensor for detecting river embank-ment collapserdquo Ice Transactions on Electronics vol 85 no 4pp 952ndash960 2002

[22] Y Qiu Q-B Wang H-T Zhao J-A Chen and Y-Y WangldquoReview on composite structural health monitoring based onfiber bragg grating sensing principlerdquo Journal of ShanghaiJiaotong University (Science) vol 18 no 2 pp 129ndash139 2013

[23] A Klar and R Linker ldquoFeasibility study of automated de-tection of tunnel excavation by brillouin optical time domainreflectometryrdquo Tunnelling and Underground Space Technol-ogy vol 25 no 5 pp 575ndash586 2010

[24] J Chai Y Y Sun Y Y Qian J Song W C Ma and Y LildquoStrata movement testing based on FBG-BOTDA combinedsensing technology in similar modelrdquo Journal of Xian Uni-versity of Science and Technology vol 36 no 1 pp 1ndash7 2016in Chinese

[25] J Chai Q Liu J Liu and D Zhang ldquoOptical fiber sensorsbased on novel polyimide for humidity monitoring ofbuilding materialsrdquo Optical Fiber Technology vol 41pp 40ndash47 2018

[26] J Chai Y Y Yang Y B Ouyang D D Zhang W G Du andS J Li ldquoComparative study of optical measurement methodsfor deformation and failure simulation test of overburden instoperdquo Journal of China Coal Society vol 47 pp 1ndash11 2020 inChinese

[27] Y Liu W Li J He S Liu L Cai and G Cheng ldquoApplicationof brillouin optical time domain reflectometry to dynamicmonitoring of overburden deformation and failure caused byunderground miningrdquo International Journal of Rock Me-chanics and Mining Sciences vol 106 pp 133ndash143 2018

[28] B Madjdabadi B Valley M B Dusseault and P K KaiserldquoExperimental evaluation of a distributed brillouin sensingsystem for detection of relative movement of rock blocks inunderground miningrdquo International Journal of Rock Me-chanics and Mining Sciences vol 93 pp 138ndash151 2017

[29] K Kishida C H Li S B Liu and K Nishiguchi ldquoPulse pre-pump method to achieve cm-order spatial resolution inbrillouin distributed measuring techniquerdquo IEICE TechnicalReport vol 47 pp 15ndash20 2004

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

[31] W S Zhu Y Li S C Li S GWang andQ B Zhang ldquoQuasi-three-dimensional physical model tests on a cavern complexunder high in-situ stressesrdquo International Journal of RockMechanics and Mining Sciences vol 48 no 2 pp 199ndash2092011

[32] W B Suo B Shi W Zhang H L Cui J Liu and J Q GaoldquoStudy on calibration of distributed optical fiber sensors basedon BOTDRrdquo Chinese Journal of Scientific Instrument vol 27no 9 pp 985ndash989 2006 in Chinese

[33] X Xi S Yang and C-Q Li ldquoA non-uniform corrosion modeland meso-scale fracture modelling of concreterdquo Cement andConcrete Research vol 108 pp 87ndash102 2018

[34] X Xi S Yang C-Q Li M Cai X Hu and Z K ShiptonldquoMeso-scale mixed-mode fracture modelling of reinforcedconcrete structures subjected to non-uniform corrosionrdquoEngineering Fracture Mechanics vol 199 pp 114ndash130 2018


disturbed overburden rupture and migration afteroverburden structural change in steeply inclined coalseams mining are very topical

+e PAM approach envisages deformation monitoringvia total stations dial gauges strain gauges and so forthwhose testing accuracy and sensitivity need further im-provement most of them use point monitoring while thelayout of points and lines is too complicated In generaldeformation monitoring can only monitor the modelrsquossurface but fail to implement internal monitoring With therapid development of acoustic emission (AE) nondestructivedetection technology numerous researchers had success-fully used it to detect the number of events and energy ratesof the PAM when the chasm slips were unstable [10] +eyobtained the precursor information of chasm instability andrevealed the characteristics and dynamic response laws ofstope pressure before and after the activation of chasms [11]Besides the AE technology was also utilized in the assess-ment of characteristics of the spatial-temporal evolution ofdynamic instability of large-inclination coal and rock masses[12 13 14 15 16] Another hot field of research is fibersensing technology which can achieve long-distance dis-tributed monitoring Using the advantages of anticorrosionantielectromagnetic interference small size lightweighthigh sensitivity high precision and so forth it ensures thestability monitoring for geotechnical [17 18] geology[19 20] water conservation [21] aerospace [22] defense[23] and other applications References [24ndash26] incorpo-rated the optical fiber sensing technology into the logicalphysical model to monitor the deformation and weighting ofworkface overburden which yielded interesting findings+is technology has been successfully applied to the mon-itoring of overburden migration in coal mine goaf [27 28]

In this study the PAM AE and distributed fibersensing (DBS) are jointly applied to steeply inclined coalseams for assessing the disturbed overburden secondarydeformation and rupture patterns as well as the char-acteristics of sound and light response in the process ofrock deformation and rupture +is research can provide atheoretical reference for the prevention of hazards such asrib spalling roof falling and support instability +eresearch results are considered instrumental in the AE andDBS detection of rock and soil structure deformation anddamage

2 Principles of Acoustic and OpticalDetection Methods

21 AE-Based Positioning by Time Differences Positioningby time differences is aimed to determine the soundsourcersquos coordinates or position by measuring the pa-rameters of each AE channel signal TDOA wave speedand sensor spacing and their processing via a certainalgorithm +is accurate yet complicated positioningmethod has been widely applied in component detectionsWhen performing planar positioning on a diamond arraycomposed of four AE sensors AE can obtain a real po-sitioning sound source as shown in Figure 1 In actualcomponent AE monitoring the number of AE sensors

often exceeds four If an individual AE sensor fails duringmonitoring the remaining four AE sensors can stillmonitor a real positioning sound source

Assume that the hyperbolic curve 1 is obtained from thetime difference ΔtX between S1 and S3 AE sensors thehyperbolic curve 2 is obtained from the time difference ΔtYbetween S2 and S4 AE sensors the positioning sound sourceis Q the distance between S1 and S3 sensors is a the distancebetween S2 and S4 sensors is b and the wave velocity is V+en the positioning sound source is located at the inter-section point Q (X Y) of the two hyperbolae and its co-ordinates can be expressed as follows

X ΔtXV

2aLX + 2

X minusa

21113874 1113875

2+ Y

2

1113971

⎡⎢⎢⎣ ⎤⎥⎥⎦

Y ΔtYV

2bLY + 2

Y minusb

21113888 1113889

2

+ X2

11139741113972

⎡⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎢⎣

⎤⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎥⎦

(1)

22 Optical Fiber Sensing Measurements DBS uses opticalfibers as sensing elements When the measured fiber issubjected to an external force or temperature variations thefrequency of the stimulated Brillouin scattered light in thefiber will change +e strain data transferred along the fibercan be obtained by conversion +e relationship between theBrillouin frequency shift temperature and strain is [29]

Δε ΔVB minus C1ΔT( 1113857

C2 (2)

where ΔVB is Brillouin frequency shift MHz C1 is tem-perature sensitivity coefficient MHzdegC C2 is strain sensi-tivity coefficient MHzμε ΔT is temperature variation degCand Δε is strain variation +is method is based on theprinciple of light scattering and measures the frequencychange of Brillouin scattered light

It is generally believed that when the temperature var-iation is within 5degC the Brillouin frequency shift caused bythe temperature can be ignored In this study this test is

X

Y

Q(X Y)

12

S4

S1

S2

S3

a

b

Figure 1 +e AE sound source positioning of an array composedof four AE sensors


















Rockproperty


Elasticmodulus(GPa)

Cohesion(MPa)


(deg)

Poissonrsquosratio

Similarityratio


Lime Gypsum Water


Finesandstone 7008 1532 268 38 015 6 6 4 3448 345 230 402

Sandymudstone 3563 951 122 30 028 7 7 3 4770 477 204 545


Main roof



13-1 coal seam

Immediate floor


loading device

960620230050760090040600720680250440300460220650

Sandy mudstone


Fine sandstone

Sandy mudstone

Sandy mudstone

Sandy mudstone

Siltstone


Siltstone


N24m

China

Anhui province


25m

90m 120m

2m

13 coal

5m

Tailentry

Headentry 40deg

Upp

er sl

ice

Botto

m sl

ice

Cata

clasti

c reg

ener

ated

roof











analyzer


AE sensors



10

50 p1

p2

p3

p4

p5

p6






A-A

A-A

Arsquo-Arsquo

B-B

B-B

Brsquo-Brsquo



Transverse and

longitudinal cracks


Bed separation

Rib spalling












Abrupt change

Abrupt change

Abrupt change

0

1

2

3

4

5

AE

ener

gy (1

03 mV

mS)

Disturbedhigh-level


0

1

2

3

4

5

6

7

AE

even

t cou

nt (1

02 n)

0

1

2

3

4

5

6

7

8

Cum

ulat

ive A

E co

unt (

103 )

Firstenergypeak

Secondenergypeak

Thirdenergypeak

Fourthenergypeak

Fifthenergypeak

Sixthenergypeak

Disturbedmain roof

breaksDisturbed

overburdenslips

200 400 600 800 10000Duration (s)







20

140

120

100

80

60

40

20

0

Phys

ical

mod

el h

eigh

t (cm

)




Disturbed maim roof

breaks








1500

1200

900

600

ndash500 ndash1500 0 500 1500 2500

300

0

Phys

ical

mod

el h

eigh

t (m

m)

Strain (με)

Optical fiber




(a)

1500

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)



Optical fiber

(b)

1500 Optical fiber

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)





(c)





5 Conclusions







Data Availability




Acknowledgments


References





















































Rockproperty


Elasticmodulus(GPa)

Cohesion(MPa)


(deg)

Poissonrsquosratio

Similarityratio


Lime Gypsum Water


Finesandstone 7008 1532 268 38 015 6 6 4 3448 345 230 402

Sandymudstone 3563 951 122 30 028 7 7 3 4770 477 204 545


Main roof



13-1 coal seam

Immediate floor


loading device

960620230050760090040600720680250440300460220650

Sandy mudstone


Fine sandstone

Sandy mudstone

Sandy mudstone

Sandy mudstone

Siltstone


Siltstone


N24m

China

Anhui province


25m

90m 120m

2m

13 coal

5m

Tailentry

Headentry 40deg

Upp

er sl

ice

Botto

m sl

ice

Cata

clasti

c reg

ener

ated

roof











analyzer


AE sensors



10

50 p1

p2

p3

p4

p5

p6






A-A

A-A

Arsquo-Arsquo

B-B

B-B

Brsquo-Brsquo



Transverse and

longitudinal cracks


Bed separation

Rib spalling












Abrupt change

Abrupt change

Abrupt change

0

1

2

3

4

5

AE

ener

gy (1

03 mV

mS)

Disturbedhigh-level


0

1

2

3

4

5

6

7

AE

even

t cou

nt (1

02 n)

0

1

2

3

4

5

6

7

8

Cum

ulat

ive A

E co

unt (

103 )

Firstenergypeak

Secondenergypeak

Thirdenergypeak

Fourthenergypeak

Fifthenergypeak

Sixthenergypeak

Disturbedmain roof

breaksDisturbed

overburdenslips

200 400 600 800 10000Duration (s)







20

140

120

100

80

60

40

20

0

Phys

ical

mod

el h

eigh

t (cm

)




Disturbed maim roof

breaks








1500

1200

900

600

ndash500 ndash1500 0 500 1500 2500

300

0

Phys

ical

mod

el h

eigh

t (m

m)

Strain (με)

Optical fiber




(a)

1500

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)



Optical fiber

(b)

1500 Optical fiber

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)





(c)





5 Conclusions







Data Availability




Acknowledgments


References








































Rockproperty


Elasticmodulus(GPa)

Cohesion(MPa)


(deg)

Poissonrsquosratio

Similarityratio


Lime Gypsum Water


Finesandstone 7008 1532 268 38 015 6 6 4 3448 345 230 402

Sandymudstone 3563 951 122 30 028 7 7 3 4770 477 204 545


Main roof



13-1 coal seam

Immediate floor


loading device

960620230050760090040600720680250440300460220650

Sandy mudstone


Fine sandstone

Sandy mudstone

Sandy mudstone

Sandy mudstone

Siltstone


Siltstone


N24m

China

Anhui province


25m

90m 120m

2m

13 coal

5m

Tailentry

Headentry 40deg

Upp

er sl

ice

Botto

m sl

ice

Cata

clasti

c reg

ener

ated

roof











analyzer


AE sensors



10

50 p1

p2

p3

p4

p5

p6






A-A

A-A

Arsquo-Arsquo

B-B

B-B

Brsquo-Brsquo



Transverse and

longitudinal cracks


Bed separation

Rib spalling












Abrupt change

Abrupt change

Abrupt change

0

1

2

3

4

5

AE

ener

gy (1

03 mV

mS)

Disturbedhigh-level


0

1

2

3

4

5

6

7

AE

even

t cou

nt (1

02 n)

0

1

2

3

4

5

6

7

8

Cum

ulat

ive A

E co

unt (

103 )

Firstenergypeak

Secondenergypeak

Thirdenergypeak

Fourthenergypeak

Fifthenergypeak

Sixthenergypeak

Disturbedmain roof

breaksDisturbed

overburdenslips

200 400 600 800 10000Duration (s)







20

140

120

100

80

60

40

20

0

Phys

ical

mod

el h

eigh

t (cm

)




Disturbed maim roof

breaks








1500

1200

900

600

ndash500 ndash1500 0 500 1500 2500

300

0

Phys

ical

mod

el h

eigh

t (m

m)

Strain (με)

Optical fiber




(a)

1500

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)



Optical fiber

(b)

1500 Optical fiber

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)





(c)





5 Conclusions







Data Availability




Acknowledgments


References













































analyzer


AE sensors



10

50 p1

p2

p3

p4

p5

p6






A-A

A-A

Arsquo-Arsquo

B-B

B-B

Brsquo-Brsquo



Transverse and

longitudinal cracks


Bed separation

Rib spalling












Abrupt change

Abrupt change

Abrupt change

0

1

2

3

4

5

AE

ener

gy (1

03 mV

mS)

Disturbedhigh-level


0

1

2

3

4

5

6

7

AE

even

t cou

nt (1

02 n)

0

1

2

3

4

5

6

7

8

Cum

ulat

ive A

E co

unt (

103 )

Firstenergypeak

Secondenergypeak

Thirdenergypeak

Fourthenergypeak

Fifthenergypeak

Sixthenergypeak

Disturbedmain roof

breaksDisturbed

overburdenslips

200 400 600 800 10000Duration (s)







20

140

120

100

80

60

40

20

0

Phys

ical

mod

el h

eigh

t (cm

)




Disturbed maim roof

breaks








1500

1200

900

600

ndash500 ndash1500 0 500 1500 2500

300

0

Phys

ical

mod

el h

eigh

t (m

m)

Strain (με)

Optical fiber




(a)

1500

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)



Optical fiber

(b)

1500 Optical fiber

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)





(c)





5 Conclusions







Data Availability




Acknowledgments


References








































A-A

A-A

Arsquo-Arsquo

B-B

B-B

Brsquo-Brsquo



Transverse and

longitudinal cracks


Bed separation

Rib spalling












Abrupt change

Abrupt change

Abrupt change

0

1

2

3

4

5

AE

ener

gy (1

03 mV

mS)

Disturbedhigh-level


0

1

2

3

4

5

6

7

AE

even

t cou

nt (1

02 n)

0

1

2

3

4

5

6

7

8

Cum

ulat

ive A

E co

unt (

103 )

Firstenergypeak

Secondenergypeak

Thirdenergypeak

Fourthenergypeak

Fifthenergypeak

Sixthenergypeak

Disturbedmain roof

breaksDisturbed

overburdenslips

200 400 600 800 10000Duration (s)







20

140

120

100

80

60

40

20

0

Phys

ical

mod

el h

eigh

t (cm

)




Disturbed maim roof

breaks








1500

1200

900

600

ndash500 ndash1500 0 500 1500 2500

300

0

Phys

ical

mod

el h

eigh

t (m

m)

Strain (με)

Optical fiber




(a)

1500

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)



Optical fiber

(b)

1500 Optical fiber

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)





(c)





5 Conclusions







Data Availability




Acknowledgments


References










































Abrupt change

Abrupt change

Abrupt change

0

1

2

3

4

5

AE

ener

gy (1

03 mV

mS)

Disturbedhigh-level


0

1

2

3

4

5

6

7

AE

even

t cou

nt (1

02 n)

0

1

2

3

4

5

6

7

8

Cum

ulat

ive A

E co

unt (

103 )

Firstenergypeak

Secondenergypeak

Thirdenergypeak

Fourthenergypeak

Fifthenergypeak

Sixthenergypeak

Disturbedmain roof

breaksDisturbed

overburdenslips

200 400 600 800 10000Duration (s)







20

140

120

100

80

60

40

20

0

Phys

ical

mod

el h

eigh

t (cm

)




Disturbed maim roof

breaks








1500

1200

900

600

ndash500 ndash1500 0 500 1500 2500

300

0

Phys

ical

mod

el h

eigh

t (m

m)

Strain (με)

Optical fiber




(a)

1500

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)



Optical fiber

(b)

1500 Optical fiber

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)





(c)





5 Conclusions







Data Availability




Acknowledgments


References









































20

140

120

100

80

60

40

20

0

Phys

ical

mod

el h

eigh

t (cm

)




Disturbed maim roof

breaks








1500

1200

900

600

ndash500 ndash1500 0 500 1500 2500

300

0

Phys

ical

mod

el h

eigh

t (m

m)

Strain (με)

Optical fiber




(a)

1500

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)



Optical fiber

(b)

1500 Optical fiber

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)





(c)





5 Conclusions







Data Availability




Acknowledgments


References








































1500

1200

900

600

ndash500 ndash1500 0 500 1500 2500

300

0

Phys

ical

mod

el h

eigh

t (m

m)

Strain (με)

Optical fiber




(a)

1500

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)



Optical fiber

(b)

1500 Optical fiber

1200

900

600

300

0

Phys

ical

mod

el h

eigh

t (m

m)

ndash500 ndash1500 0 500 1500 2500

Strain (με)





(c)





5 Conclusions







Data Availability




Acknowledgments


References







































5 Conclusions







Data Availability




Acknowledgments


References



































































Documents

RuptureandMigrationLawofDisturbedOverburdenduring ...downloads.hindawi.com/journals/ace/2020/8863547.pdf · 2020. 10. 8. · ResearchArticle RuptureandMigrationLawofDisturbedOverburdenduring