studyonroof-coalcavingcharacteristicswithcomplicated...

Research ArticleStudy on Roof-Coal Caving Characteristics with ComplicatedStructure by Fully Mechanized Caving Mining

Yunpei Liang 1 Lei Li12 Xuelong Li 1 Kequan Wang2 Jinhua Chen2

Zhongguang Sun12 and Xuelin Yang 12

1State Key Laboratory of Coal Mine Disaster Dynamics and Control College of Resources and Environmental ScienceChongqing University Chongqing 400044 China2National Key Laboratory of Gas Disaster Detecting Preventing and Emergency ControllingChongqing Research Institute of China Coal Technology and Engineering Group Crop Chongqing 400037 China

Correspondence should be addressed to Xuelong Li lixlcumt126com

Received 27 December 2018 Accepted 20 March 2019 Published 18 April 2019

Academic Editor Radoslaw Zimroz

Copyright copy 2019 Yunpei Liang 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

With mining technology and mechanization degree being improving fully mechanized caving mining technology (FCM) hasbecome a main method for thick coal seam extraction in China However roof-coal caving characteristics in turn restrict itsrecovery efficiency especially for the coal seamwith complicated structure (CCS) that is the coal seam comprises hard or soft coaland gangue In order to explore the key factors influencing the roof-coal caving and recovery characteristics related research workhas been conducted as follows firstly a mechanical model of CCS has been established which indicates the strength of the coaland gangue will directly affect the roof-coal recovery Meanwhile based on the geological settings of Qinyuan coal minenumerical simulation on roof-coal caving law under different thicknesses of hard or soft coal and gangue has been performedusing UDEC software-e results show that the maximum principal stress will increase with the increase of mining depth makingthe roof-coal to break easily Furthermore the range of the plastic zone of the top coal and the damage degree of the top coalincrease with the increase of mining depth Physical modeling results show that when an extraction-caving ratio is 1 the numberof times the coal arch forms is 043 at every caving up to a maximum of 3 the number of times coal arch forms with an extraction-caving ratio of 2 is 465 times larger than that with an extraction-caving ratio of 1 -e probability of coal arch formation with anextraction-caving ratio of 3 is minimal about 04 which is due to that the arch span is large and the curvature is small so it isdifficult to form a stable arch structure According to the mechanical characteristics of roof-coal in Qinyuan coal mine deep-holeblasting technique has been used to reduce the fragments of roof-coal crushed-e results show that this technique can effectivelyimprove the recovery of roof-coal

1 Introduction

-ick coal seam (ge35m) reserves account for 45 of coalreserves in China which has great advantages in terms ofresource reserves [1ndash4] In recent years with the im-provement of FCM technology it has been the main methodfor thick coal seam extraction [5ndash8] -is technique mainlyinvolves two steps first a layer of coal with a thickness of2ndash3m at the bottom will be mined using the conventionalmining method then under the action of mining stopepressure the coal unmined at the high layer (roof-coal) willbe fragmented and recovered by the function of self-gravity

[9ndash12] As the main method for thick coal seam extraction[13ndash15] FCM has main advantages of high production highefficiency less roadway excavation low energy consump-tion etc [16 17] -erefore it has a wide applicationprospect in China [18 19]

Although this technique has the mentioned advantagesit also has obvious shortcoming of caving problem [20ndash22]which not only directly affects the difficulty of roof cavingand recovery but also determines the applicability of thistechnology in certain geological conditions and provides keyparameters for this technology and then effectively improvesthe roof-coal recovery [23ndash26] -ere are major factors

HindawiShock and VibrationVolume 2019 Article ID 6519213 20 pageshttpsdoiorg10115520196519213

affecting roof-coal caving including the uniaxial compres-sive strength (σc) the thickness of coal seam the develop-ment of joint fractures in coal seam etc

-e strength of coal seam mainly reflects the self-abilityto resist damage which determines the fragmentation de-gree of roof-coal under the action of mining stope pressureAnd the fragmentation degree of roof-coal will directly affectthe roof-coal recovery During the extraction of hard coaldue to that the mining stope pressure cannot effectivelyfragment the roof-coal the roof-coal blocks are too large toreach the requirement of top coal caving which will reducethe roof-coal recovery [27ndash30]

-in top coal is a pseudo-top and it is difficult to controlit from falling in the tail of the bracket which will lead todirect crushing ahead of the top it would mix with the topcoal when released to the coal outlet through which not onlythe coal quality will be affected but also a large number of topcoal will be lost in the goaf overthick top coal is hard to befully loose in the top control area so it is difficult to fall in thefalling area In particular with the gradual increase in thethickness of coal seams being exploited the mine pressure inthe fully mechanized subsidence stope is becoming moreintense Whether the large-scale top coal body can bebroken fallen or released under the action of mine pressurethe height of the fully mechanized top coal caving face can beachieved -e production rate has become a key technicalproblem that restricts the use of fully mechanized sublevelcaving mining in extremely thick coal seams and even thickcoal seams [19 31ndash33]

According to on-site observations the weakest surface ofthe coal affected by top coal caving in fully mechanized topcoal caving face is the joints bedding and fractures of coalObviously coal seams with joints and fissures developed havepoor integrity of the coal body and the overall strength isreduced -e top coal is easily broken under the influence ofsupporting pressure At the same time the more dense thefissures are the more easily the top coal is broken and thesmaller the degree of eruption is the more favorable it is torelease that is the better the release of top coal and vice versa[33ndash35] In addition the top coal caving is also related to theperiod of the roof the depth of the coal seam the hardness ofthe coal seam the amount of sand and the filling factor

In recent years with the development of science andtechnology more and more advanced technological methodshave been introduced into the research of fully mechanizedcaving mining [36] Especially in the aspect of evaluationmany advanced calculation theories and methods are grad-ually introduced into the top coal evaluation For example thegray-fuzzy evaluation method is used to study that the steepseam coal can be relegated and fuzzy mathematics theory isused to classify the caving of top coal under different coalseam conditions [37] Chen et al [38] used the basic conceptsof damage mechanics to describe the relationship betweendamage and release of top coal Wang et al [39] used theartificial intelligence as a reference to establish an artificialneural network process of top coal disruptive identification insteep-inclined coal caving roof caving-e above new theoriesand methods not only have their own characteristics but alsohave their certain deficiencies For example the fuzzy

comprehensive evaluation method often requires certainsubjectivity and randomness when determining the degree ofmembership and giving different weight to each index -eartificial neural network method has some shortcomings inslowing convergence rate easy falling into local optimum andhidden layer determination with subjectivity Support vectormachine to determine the boundary anti-interference abilityis poor and sensitive to noise data To this end we also need toexplore a more scientific and effective evaluation method oftop coal emission -e factors influencing the runoff of topcoal are complex diverse and nonlinear so it is hard to comeup with accurate and general discriminant criteria

At present fully mechanized top coal caving mining canbe applied to coal seams with better geological conditionsDuring the fully mechanized top coal caving mining ofcomplex structure thick coal seams due to the presence ofentrainment and hard coal coal seams often have largefracture fragments difficult top coal release and poor topcoal deployment In order to study the law of breakingreleasing and destabilization of top coal with complexstructures this paper selects the representative geology andproduction conditions of Qinyuan coal mine in Baoji cityChina Adopting the method of combining theoreticalanalysis laboratory simulation and numerical simulationroof breaking and releasing rules of top coal and technicalparameters of caving in fully mechanized top coal cavingmining with complex structure and thick coal seam thefollowing studies are conducted

(1) -e research results of predecessors are combinedand the breaking characteristics of top coal in fullymechanized caving mining with thick seam ofcomplicated structure are analyzed In terms of theactual stress conditions of hard coal gangue in thefully mechanized top coal cavingmining the stabilityof the hard coal gangue (the hard coal delaminationor the gangue in the top coal body) is studied themechanical model of the corresponding hardenedcoal gangue is established Based on this thecrushing effect of the hardened coal gangue and thetop coal caving are analyzed

(2) -e law of breaking and instability of top coal in fullymechanized top coal caving mining with compli-cated structure and thick seam is analyzed y meansof discrete element numerical simulation methodstress field displacement field and distributioncharacter of the failure field are analyzed emphati-cally -e crushing effect of top coal and the top coaldischarge are analyzed -e law of breaking anddestabilization of top coal in fully mechanized topcoal caving mining with complicated structure isobtained

(3) -e simulation of laboratory bulk as a researchmethod is performed and the technical parametersof fully mechanized caving mining with thick coalseam with complex structure are studied Analyzethe coal gangue emanation form and top coal fallingin the process of arching and reach the complexstructure of the law of the top coal emission And put

2 Shock and Vibration

forward the corresponding weakening of the top coalin the hard coal gangue technical measures to im-prove the top coal caving

(4) -e geology and production conditions of the N101fully mechanized caving face in Qinyuan coal mine iscombined and field measurement analysis and re-search is conducted to verify the research results ofthis paper

2 Mechanical Model of Complicated Structures

Coal seams containing gangue or hard coal are often referredto as complex structural seams According to the on-siteobservations and laboratory studies it is found that duringthe fully mechanized top coal caving of complex structurethick coal seams there is a large difference in the top coalbrittleness which directly leads to the phenomenon that topcoal is often difficult to emerge during top coal caving-erefore the mechanical model of hard coal stratification orvermiculite layer in top coal is established On the one hand itcan give quantitative explanation of the breaking degree andrelease of complex structure top coal on the other hand it canbe used to solve engineering problems (top coal breakagecharacteristics of caving and drawing problems etc) andpropose engineering measures based on theoretical basis

21 Deformation Characteristics of Top Coal in ComplexStructures Regardless of whether the top coal containsholding gangue or hard top coal stratification as thethickness of the hard strata coal roof in the top coal in-creases the overall strength of the top coal increases and thefracture characteristics of the medium top coal or hard topcoal are gradually shown After the coal body deformationexceeds the peak the top coal enters the plastic deformationstate and the hard coal gangue may only enter the strengthdestruction stage With the development of the damage thestability of the plastic zone is reduced until the instability-e length of destabilization depends on the extent of theplastic zone in front of the coal wall the length of the topbeam of the support and the advancing speed of the workingface -e strength of the coal gangue is low and the granulararea of the top coal extends to the front of the coal wallwhich is unfavorable for the maintenance of the end face-e strength of the coal gangue is high and there is little partof the top coal in the granular region at the rear of thesupport that is there are few broken blocks and particlesand the top coal is very low It is usually necessary to weakenthe hard coal gangue in the top coal such as deep-holeblasting and top coal water injection to improve the char-acteristics of top coal caving and drawing in fully mecha-nized top coal caving mining In the cavities above thesupport the vertical displacement of the top coal is greaterthan the horizontal displacement -e displacement of thelow-strength hard coal gangue is much larger than that of thehigh-strength hard coal ram which indirectly reflects thephenomenon that the low-strength coal gangue is brokeninto granules and the high-hardness coal gangue is brokeninto blocks -e top coal emission is different

It is known that the difference in the strength of the hardcoal gangue makes the top coal to have different elastic-plasticzoning resulting in a great difference in the top coal brokenblock [7 24] -e top coal at the coal seam front of thecomplex structure coal seam is in the triaxial stress state andthe top coal deformation is dominated by the horizontaldeformation For the top coal with high strength and largethickness of hard coal gangue the crack development of thetop coal is relatively weaker than the strength and thicknesswhile the top coal in the top control area is dominated by thevertical displacement-e top coal with hard-bed coal gangueis not developed in the bedding and the weak side resulting indifficulty in delamination-e vertical displacement of the topcoal is lower than that of the hard coal gangue top coal withlow strength and the deformation is not obvious Besides thecoal is not fully broken and the high-strength and thick-layertop coal breaks a large block causing difficulty in dischargeand even blocking the coal opening

22 Stiffness Characteristics of Top Coal in ComplicatedStructures -e damage of the top coal after reaching thepeak strength in a complex structure depends on the degreeof the top coal deformation and the size of the top coaldeformation is determined by the stiffness of the hard coaland top coal To simplify the problem it is assumed that thestiffness of the bracket and the direct top is considered to belarge irrespective of the influence of the bracket and thedirect top (Figure 1) -en the stiffness Km of the hard layercoal gangue Kc and the top coal is analyzed

Assuming that the force in the vertical direction of hardcoal gangue and top coal is F and the total compression oftop coal is ΔS the total top coal stiffness is

K 1

1Kc( 1113857 + 1Km( 1113857

Kc middot Km

Kc + Km (1)

-en

F K middot ΔS Kc middot Km

Kc + Kmmiddot ΔS Km middot ΔSm (2)

-rough calculation the compression of hard coalgangue is ΔSm (KcKc + Km) middot ΔS

-at isΔSmΔS

Kc

Kc + Km

KcKm( 1113857

KcKm( 1113857 + 1 (3)

From equation (3) it can be seen that the percentage oftop coal deformation increases with the increase in KcKmWhen the stiffness Kc of hard coal gangue is less than the topcoal stiffness Km the top coal produces less deformationwhile the hard coal tar results in greater deformation whichis beneficial for the cracking of the hard layer coal gangueand the improvement of characteristics of top coal cavingand drawing When the top coal stiffness Km is less than thehard layer coal enthalpy stiffness Kc the hard layer coaltarpaulin will produce less deformation the old top anddirect top rotatory deformation will be absorbed by the topcoal and the top coal will be broken before the hard layercoal gangue Broken blocks block the coal open or make it

Shock and Vibration 3

difficult to break the hard coal gangue reducing the overalltop coal deployment -e comparison of the top coalstiffness Km and the stiffness Kc of the hard coal rake has asignificant effect on the fracture of the top coal in complexstructures

23 Stability Analysis of Top Coal in Complex Structures-e majority of rock formations in coal mines are sedi-mentary rocks After mining most of the surrounding rockin the mining area is dominated by gravity stress fields -efollowing is a mechanical analysis of the hard coal gangue inthe top coal in the self-weight stress field

-e hard-coal coal gangue in the top coal outside thepeak area of support pressure ahead of the complex coalseam coal wall is basically in the elastic stage -at is thehard coal gangue is located in the peak area of the supportpressure or in the top control zone Due to the high strengthand hardness of the hard layer coal gangue with the increaseof the top coal load above the support the top coal enters theplastic state under the support pressure which acts as acushion for the hard layer coal gangue and makes the topcoal relatively complete -erefore the hard coal gangue isstill in the elastic stage In the hard coal gangue remove thetiny unit and it can be treated as an elastic mediumaccording to the physical equation of the space stress state

ε3 1E

σ3 minus μ σ1 minus σ2( 11138571113858 1113859 (4)

If σ2 σ3 then

ε3 1E

(1minus μ)σ3 minus μσ11113858 1113859 (5)

Also knowε3 minusμ

σcE

(6)

Substituting (5) into (6)

minusμσ3E

1E

(1minus μ)σ3 minus μσ11113858 1113859 (7)

When finishing the hard layer coal gangue medium toreach the ultimate state of damage the elastic fracture stressformula is as follows

σ1 σc +1minus μμ

σ3 (8)

where σ1 and σ3 are the vertical and lateral stresses of hardcoal gangue respectively σc is the uniaxial compressivestrength of the hard coal gangue and μ is Poissonrsquos ratio ofthe hard coal gangue From equation (8) it can be seen thatthe elastic fracture stress value of hard coal gangue increaseswith the increase in unidirectional compressive strength andlateral stress -e formula can be translated into

σ1 σc 1μminus 11113888 1113889σ3 (9)

Similarly the formula for the elastic fracture stress at thetop stage of the coal body in front of the coal wall is

σ1prime σcprime 1μprimeminus 11113888 1113889σ3prime (10)

where σ1prime and σ3prime are the top coal vertical and lateral stressesrespectively σcprime is the unidirectional compressive strength ofthe top coal and μprime is Poissonrsquos ratio of the top coal

In the case that the hard coal gangue is combined withactual field data the values are σc = 35MPa μ = 03 K= 3c= 2500 kNm3 and H= 520m -rough calculationKcH= 39MPa and σ1 = 41MPa

From the data calculation under hard coal conditions itcan be inferred that under the effect of mining stress theabutment pressure peak is greater than the numerical valueof the elastic fracture stress of hard coal gangue -e crackdensity of the hard coal gangue will not expand and the stressvalue of the block broken in advance will not be reached

-e soft coal above the hard coal gangue is also taken asσcprime 8MPa μprime 04 K 3 c 2500 kNm3 and H 520m-rough calculation KcH 39MPa and σ1prime 34MPa

From the calculation of data under soft coal conditionswe can see KcHgt σ1prime that is when the peak bearing pressureis greater than the soft coal elastic fracture stress value thecrack density of the hard coal gangue expands and penetratesand the overall strength decreases breaking into irregularblocks in advance

From the analysis it can be known that whether the topcoal in a complex structure contains a clamp or a hard topcoal the elastic fracture stress value of a hard coal seam isusually greater than the elastic fracture stress value of the topcoal -at is σ1 minus σ1prime gt 0

-e comparison between the peak pressure of supportpressure and the elastic rupture stress value of soft coal gangueshows whether the hard coal gangue is cracked or not and it isdifficult to describe the degree of rupture -e uniaxialcompressive strength values of hard coal gangue and soft coalare fixed and the concept of rupture factor is introducednamely the ratio of the peak value of the leading supportpressure and the uniaxial compressive strength -e value is

i KcH

σc

iprime KcH

σcprime

(11)

where i is the hard coal failure factor and iprime is the soft coalfracture factor

1

F

F

2

Figure 1 Stiffness of the series system between hard coal gangueand top coal (1) Top coal stiffness Km (2) Hard layer coal ganguestiffness Kc


When the support pressure peak value KcH is 39MPathe hard coal in the hard coal slag is selected as the rep-resentative study -e uniaxial compressive strength σc thehard coal fracture coefficient i and the soft coal fracturecoefficient iprime are shown in Table 1

As can be seen from Figure 2 the hard coal failurecoefficient i and the soft coal rupture factor iprime are stronglyrelated to their respective compressive strength values andare exponentially related While hard coal usuallyσc ge 30MPa when σc ge 30MPa the hard coal failure factor i

in the hard coal gangue has a maximum of 13 -at is as thevalue of the uniaxial compressive strength of hard coalincreases i decreases and the closer to the maximum thelarger the i the better the cracking effect of the hard coalWhile soft coal usually σc le 10MPa when σc 10MPa thesoft coal fracture coefficient iprime has a minimum value 39 thatis as the uniaxial compressive strength of soft coal decreasesiprime increases and the farther away from the minimum thebetter the soft coal crushing effect

Top coal working face stress concentration coefficient Kis generally taken from 2 to 3 Similarly it can be concludedthat when the stress concentration factor is taken from othervalues in the same depth the hard coal fracture coefficient i

and the soft coal rupture factor iprime have the same linearcorrelation with their respective compressive strengthvalues and they also have an exponential function re-lationship -e larger the fracture coefficient i the better thecrushing effect of the hard layer coal gangue and the releaseof the top coal the larger the crumple factor iprime the better thecrushing effect of the soft top coal and the characteristics oftop coal caving and drawing

Under the certain conditions of the leading bearingpressure peak KcH the soft coal fracture coefficient iprime is afixed value and the smaller the value of iprime minus i the smaller thedifference in the breaking block of hard coal and soft coaland the better the crushing effect Both have gone throughthe process of fracture development and penetration andthen through the deformation of the top of controlled toparea the entire change process of the mechanics shows thatthere is little difference between the breaking of the hard coalgangue and the top coal -e hard layer coal gangue rupturecoefficient i is a fixed value -e larger the value of iprime minus i thesmaller the difference in the breaking layer degree betweenthe hard layer coal gangue and the soft coal the better thecrushing effect otherwise the difference in the brokenlumping degree is large and the top coal is spread outpoorly When the hard coal gangue breaking block is largerthe arch structure is easily formed during the droppingprocess and the coal opening which hinders the normal flowof the top coal Due to the large difference in the block sizethe flow rate is not balanced It is disadvantageous to flowand recovery of the top coal

3 Numerical Simulation Study

-e discrete element method was firstly proposed by CundallP A in 1971 as a discontinuous medium numerical analysismethod It can both simulate the movement of the block afterthe force and simulate the deformation state of the block itself

In this paper the numerical simulation program UDEC isused to simulate the stress strain and displacement of the topcoal during the fully mechanized top coal caving mining inthe thick seam with complex structure Its advantages lie inthe fact that firstly discrete rock masses allow large de-formations allowing sliding along joint surfaces turning andfalling out of the joints and secondly new contacts can beautomatically identified during the calculation process

31 Model Establishment According to the geologicalconditions of the N101 fully mechanized caving face ofQinyuan coal mine the model size is 220mtimes 498m and theupper boundary load is calculated by the depth of 520m-edirect top thickness is 16m the block size is 16mtimes 08mand the old top is 12m thick Breaking step distance 16mDirect bottom thickness 15m length 3m old bottomthickness 5m block size 25mtimes 5m -e simulated coalseam thickness is 87m of which the mining height is 23mand the coal laying height is 64m Because the object ofsimulation analysis is complex structure top coal in order toimprove the calculation accuracy the top coal in the middlepart of the model is encrypted the top coal contains a hardlayer coal gangue and the model divides the hard coalgangue in the coal seam For the upper middle and lowercases the top coal in the fully mechanized top coal cavingface was simulated to be fractured and unstable Here thehard coal gangue is regarded as a hard continuous medium-e control resistance of the top control zone is constantresistance and the support control distance is 4m

311 Determination of the Model Geometry -e top coal issoft coal When the thickness of the hard coal gangue is 15mthe divisional degree is 15mtimes 09m and the top coal isdivided into 083mtimes 042m When the thickness of the hardcoal gangue is 05m the division degree is 05mtimes 03m andthe top coal is divided into blocks of 098mtimes 049m Inaddition some numerical simulation conditions or param-eters in the model are analyzed in order to analyze the failureof the top coal in the complex structure coal seam underconditions of different strengths and different mining depths(H 320m H 520m and H 720m) of the hard coalgangue Adjustments were made to simulate the stress dis-tribution characteristics displacement distribution charac-teristics and failure characteristics of top coal under differentconditions in top coal

312 Selection of Rock Mechanics Parameters According tothe geological conditions of the actual working face thesurrounding rock mechanics parameters are selected asshown in Tables 2 and 3

Table 1 Hard coal failure factor i and soft coal failure factor iprime inhard coal gangue

σc 30 35 40 45 50 55 60i 13 111 098 087 078 071 065σcprime 10 8 7 6 5 4 3iprime 39 488 557 65 78 975 13


313 Determination of the Boundary ConditionsAccording to the actual occurrence conditions of the cal-culation model the boundary conditions of this calculationmodel are as follows

Upper boundary condition is is related to theoverburden gravity (sum ch) In order to facilitate the studythe distribution of the load is simplied as a uniform loade upper boundary condition is the stress boundarycondition

q sum ch 13MPa (12)

Lower boundary conditions the lower boundary con-dition of this model is the bottom plate which is simpliedas a displacement boundary condition It can move in the xdirection and the y direction is a xed hinge support that isv 0

Boundary conditions on both sides the boundaryconditions on both sides of this model are solid coal rock

0 10 20 30 40 50 60

06

07

08

09

10

11

12

13Fr

actu

re co

effic

ient

of h

ard

coal

(i)

σc (MPa)

R2 = 096755

(a)

σc (MPa)0 2 4 6 8 10

4

6

8

10

12

14

Frac

ture

coef

ficie

nt o

f sof

t coa

l (iprime)

R2 = 099926

(b)

Figure 2 Relationship between function coecients of hard and soft coal (a) Hard coal failure factor (i) function in hard coal gangue (b)Soft coal fracture factor (iprime) function

Table 2 Mechanical parameters of hard layer coal gangue in dierent layers of top coal

Rock stratum Densityd (Nmiddotmminus3)

Bulk modulusK (GPa)

Shear modulusG (GPa)

Internal frictionangle f (deg)

AdhesionC (MPa)

Tensile strengtht (MPa)

Hard coal gangue (hard coal) 1600 12 10 34 4 2Hard coal gangue (gangue) 2600 18 14 36 19 12Top coal 1300 5 22 21 1 08Overlying strata 2700 20 17 42 20 11Basic roof 2700 20 17 42 20 11Immediate roof 2500 13 10 38 10 4False roof 2100 13 7 36 8 3Direct bottom 1800 10 10 32 5 3Previous bottom 2200 19 16 40 7 4

Table 3 Mechanical parameters of contact surface between hard seam and coal seam in dierent layers of top coal

Rock stratum Normal stinessjkn (GPa)

Shear stinessjks (GPa)


Cohesive forceC (MPa)


Hard coal gangue (hard coal) 4 35 27 004 0Hard coal gangue (gangue) 14 5 29 005 0Top coal 4 3 14 002 0Overlying strata 16 6 31 007 0Basic roof 16 6 31 007 0Immediate roof 7 5 0 0 0False roof 6 45 0 0 0Direct bottom 5 6 28 006 0Previous bottom 5 6 32 01 0


bodies which are simplied as displacement boundaryconditions and canmove in the y directione x direction isa xed hinge support u 0

32 Simulation Results and Analysis

321 Stress Field Analysis Figure 3 reects the verticalstress distribution in front of the coal wall with dierentthicknesses and hard coal seams From this it can be seenthat the vertical stress has played a role in destroying the topcoal of the complex structure and this determines the degreeof fracture when the top coal reaches the top of the coal walle vertical stress of 7msim16m in front of the 15m thickhard-coal coal gangue coal wall is in the peak position thatis the peak support pressure area e vertical stress in-creases quickly from 16m to 24m in front of the coal walland the vertical stress gradually goes to the original rockstress at 24me vertical stress at 18m in front of the 05mthick hard coal gangue coal gangue reaches the peak pointand the vertical stress is less than the 15m thick verticalboring coal gangue stress valuee peak zone is 05m thickand hard coal gangue is at and far from the coal wall It canbe seen that the supporting pressure of the 15m thick hardcoal gangue shows the distribution characteristics of theabutment pressure of the hard top coal and the supportingpressure of the 05m thick hard tar coal gangue shows thedistribution characteristics of the abutment pressure of thehard top coal

Figure 4 shows the distribution of shear stress in dif-ferent layers of coal seams with 15m thickness and dierentstrengths From the analysis and comparison in Figure 5 themaximum shear stress value of the 15m thick medium-hardlayer coal gangue is higher than themaximum shear strengthvalue of 458MPa and the breaking eect of hard coalgangue and top coal is good and the high-strength coalgangue develops the shear stress Basically the pressure-shear stress occurs and the tensile shear stress region issmall e tensile shear stress and the compressive shearstress of the medium-strength hard coal gangue exist

Figure 5 shows the maximum and minimum principalstress dierence curves for dierent layers of 15m thickmedium-strength hard-coal coal gangue Shear stress can beexpressed as a function of the relationship between themaximum principal stress and the minimum principalstress e strength of the top coal and hard layer coalgangue in the peak support pressure area continuouslydecreases When the hard coal gangue is in the lower part ofthe top coal the main stress dierence is the largest At thistime the hard coal gangue is aected by the large shear layercoal gangue e main stress dierence is the largest at isthe shear fracture occurs the principal stress (maximumprincipal stress andminimum principal stress) in the controltop area reduces rapidly the overall rigidity also reduces thebreaking block is small and the breaking eect is goodwhich make the top coal to fall smoothly When the hardcoal gangue is in the middle and upper part of the top coalthe variation of the principal stress dierence is lower thanthat in the lower e hard coal gangue has a poor breaking

eect a large block size or a cantilever structure resulting inpoor top coal deployment

As shown in Figure 6(a) the maximum principal stressof the top coal in the 15m thick medium-hard layer coalgangue with depthH 320m is 8m away from the coal wallWhen the burial depth isH 520m the maximum principalstress of the top coal is 6m away from the coal wall andwhen the burial depth is H 720m the maximum principalstress of the top coal is 11m away from the coal wall Withthe increase in the depth of the top coal the maximumprincipal stress value also increases but the plastic mobilityof the top coal increases the bearing capacity decreases andthe maximum principal stress decreases with the depthH 720m

As shown in Figure 6(b) with the increase of the depth ofthe top coal the maximum principal stress value also in-creases Under the condition of burial depth of H 720mthe top coal in the area of 8 to 10m in front of the coal wallcannot withstand the old top e slewing pressure reducesthe maximum principal stress

322 Displacement Field Analysis In the case of upper hardcoal gangue the subsidence rate of the top coal with smallbreaking block is faster than that of the hard layer coalgangue with large breaking fragment while the top coalblock reaches the coal before the hard coal lumping block(Figure 7) ere has no eect on the release of top coal Inthe middle hard layer coal gangue condition the top coalbelow the hard coal gangue is smoothly and quickly releasedwith the shift frame the middle hard layer coal gangue formsthe delamination and the intermediate hard gangue coalgangue breaks insuciently and breaks the fragmentationdegree big Because the lower speed of the hard coal gangueblock is slower than that of the top coal it will hinder the topcoal body and the top coal above the hard coal gangue willlag behind erefore the top coal will have poor cavingcharacteristics

Hard coal with a thickness of 05mHard coal with a thickness of 15m

0

5

10

15

20

25

30

35

40

Vert

ical

stre

ss (M

Pa)

10 20 30 400Distance from the coal wall (m)

Figure 3 Vertical stress of the coal body in front of coal wall withdierent thicknesses of hard coal seam


A vertical displacement of 05m thick high-strengthhard-coal coal gangue is shown in Figure 8When the upper hard coal gangue is above the top controlzone the vertical displacement of each layer of top coal islarger and the dierence is small Similarly while the topcoal is broken fully the existence of the upper hard coalgangue does not aect the release of the top coal When thehard coal gangue is in the middle position its verticaldisplacement with the upper coal is basically the same whichis obviously less than the vertical displacement of the lowercoal which indicates that themiddle hard coal gang preventsthe deformation of the upper coal And it aects the ow ofthe upper top coal but does not aect the lower top coal

e vertical displacements of the upper and lower topcoal with dierent depths in the 15m thick medium-strength hard coal gangue are shown in Figure 9 As canbe seen from that with the increase of mining depth thegreater the vertical displacement of the top coal in the samelayer the greater the deformation of the top coal the higherthe destruction of the top coal and the better the de-ployment of the top coal e vertical deformation of the topcoal in the top control area is greater than the top coaldeformation in front of the coal wall because the de-formation of the top coal in front of the coal wall isdominated by the horizontal displacement

4 Sparse Similarity Simulation

41 Basic Principles and Methods e dissociation modelexperiment combined with the site conditions of the coalmine according to the similarity theory designed the modelwith certain similarity ratio in the laboratory measured themodel data and analyzed them

Geological and production conditions of the N101 fullymechanized top coal caving face in Qinyuan coal mine (1)the coal seam is a special thick coal seam and the top coalthickness changes greatly (2) the coal seam is directlytopped with a mudstone coal and rock interbed with athickness of 157m the direct bottom is a mudstone with athickness of 129m the bottom of the coal seam the coalseam and the roof have a lower strength and is a ldquothree softrdquocoal seam (3) the structure of the coal seam is complex andthe soft and hard are dierent e top coal in each layer ofthe coal seam is top-bottom coal (soft coal) top-middle topcoal (hard coal) and medium top coal (soft coal) from top tobottom along the thickness direction Middle and lower topcoal (hard coal) and lower top coal (soft coal) are as shown inFigure 10 (4) the average coal thickness in the working face

TopMiddleBottom

ndash6

ndash4

ndash2

0

2

4

6

8Sh

earin

g str

engt

h (M

Pa)

5 10 15 200Distance from the wall (m)

(a)

TopMiddleBottom

ndash4

ndash3

ndash2

ndash1

0

1

2

Reco

very

rate

()


(b)

Figure 4 Distribution of shear stress in dierent layers of coal seam with 15m thickness and dierent strength (a) medium-strength and(b) high-strength hard coal gangue

TopMiddleBottom

ndash5

0

5

10

15

20

25

30

35

40

Diff

eren

ce b

etw

een

the m

axim

um p

rinci

pal

stres

s and

the m

inim

um p

rinci

pal s

tress

(MPa

)

2 4 6 8 10 120Distance from the wall (m)

Figure 5 Curve of maximum and minimum principal stresses ofdierent layers of 15m thick medium-hard layer coal gangue


is 87m the mining height is 23m and the top coalthickness is 64m (5) work face bracket adopts ZF55001728HQ-type anti-four-barlow-cutting top coal support

In the mechanized top coal caving face the formation ofthe top coal crushing block is the result of overburden rockbearing pressure old roof rotation deformation and re-peated support of the support e destruction of top coal isdeveloped from the bottom-up e lower coal is supportedby pressure of the larger support e degree of fragmen-tation above the support is smaller than that of the upperfragment At the same time due to the presence of high-strength hard top coal in coal seams the fragmentation of

hard coal seams is larger than that of soft coal seams but atthe same time the fragmentation of soft coals at upperpositions is larger than that of lower soft coals Table 4 showsthe top coal fragmentation at dierent levels measured onthe site of the N101 fully mechanized top coal caving face

42 Model Establishment e frame size used in the ex-periment is 130 cm in length and 12 cm in width e widthof the top coal support used in the site is 15m Consideringthe content of the study and the number of coal deposits permodel the width of the model frame is taken as the width ofthe two simulated supports in the model at is the width

H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss


(a)

H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss (M

Pa)


(b)

Figure 6 Maximum principal stress of (a) top coal and (b) lower coal with 15m thick medium-strength hard coal gangue at dierentdepths

Vert

ical

disp

lace

men

t (m

m)

05m hard coal on top05m hard coal in middle05m hard coal at bottom

ndash2 0 2 4ndash4Distance from the wall (m)

150

0

50

100

200

250

300

350

400

Figure 7 Vertical displacements of 05m thick high-strengthmedium-strength coal seam and top coal

Vert

ical

disp

lace

men

t (m

m)

MiddleBottom


200

0

100

300

400

500

Figure 8 Vertical displacements of coal seams and top coal with05m high-strength upper hard layers


of the simulated support is 6 cm erefore the geometricsimilarity between the model and the prototype is Cl 61501 25

Two angle steels are erected on the level of the coalopening and a 24 cm wide steel bar is laid on it to simulatethe shear depth of the coal face of the working face in themodel experiment each stratied layer was laid horizontallyand gray coal with dierent particle sizes was selected for thetop coal and a thin black marker layer stone was laid be-tween soft and hard top coal layers e top and bottomlayers of the direct roof are selected from dierent particlesizes and dierent color stones respectively red and white

as shown in Figure 11 Specic actual dimensions and modeldimensions are shown in Tables 5 and 6 respectively

In the model making process the front of the model iscovered with plexiglass and the rear is xed with layeredangle steel In order to simulate the on-site coal cavingprocess a special low-level caving coal support was used tosimulate the actual propulsion and coal-discharging processe weighted volume of the top coal and the direct roof inthe model experiment was calculated in the natural state (seeTable 7 for data)

During the experiment 10 cmwas left on each side of themodel to eliminate the boundary eect and taking into

Ver

tical

disp

lace

men

t (m

m)

H = 320mH = 520mH = 720m


0

200

400

600

800

1000

(a)

H = 320mH = 520mH = 720m

Ver

tical

disp

lace

men

t (m

m)


0

200

400

600

800

1000

(b)

Figure 9 Vertical displacements of dierent layers of top coal with dierent thickness in 15m thick medium-strength hard coal gangue (a)Upper top coal (b) Lower top coal

Strata Lithology Thickness

Sandstone

Mudstoneand coal

Mudstone

Coal

Sandymudstone

Mudstone

(a) (b)

157

107

129

49

1091

95

Coal seam

17

25

185

23

115

Hardness

Soft

Hard

Soft

Hard

Soft

Figure 10 (a) Coal seam comprehensive column shape at N101 fully mechanized caving face in Qinyuan coal mine (b) Top coal schematic


account the control roof distance of the support the ef-fective length of the model coal drop test is 90 cm thenthe number of coal throwing for each experiment of threecoal placement steps 90144 6 times Because threemodels of coal caving can be experimented on a singlemodel the experiment of the top coal emission law of thethree-soft complex structure coal seam only needs to lay amodel

43 Experimental Procedure -e coal laying simulationprocess is as follows

(1) Install a coal-spraying support that is place thesupport in the high-elevation space in the lower partof the model

(2) Install a baffle to seal the space behind the support(gob)

Table 4 Measured top coal block size

Horizon Measuringpoint 1

Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6

-e lower top coal fragmental size (cm) 10 13 16 12 17 10-e middle and lower top coal fragmentalsize (cm) 42 47 49 46 50 40

-e middle top coal fragmental size (cm) 18 20 21 18 23 16-e middle and upper top coal fragmentalsize (cm) 48 52 53 50 58 45

-e upper top coal fragmental size (cm) 23 26 28 25 32 23

Figure 11 Overview of the experimental model of complex structure coal seam

Table 5 Hydraulic support dimensions

Width Mining height Minimum control topdistance Height of coal caving Cutting depth of coal

shearerActual (m) Model (cm) Actual (m) Mod (cm) Actual (m) Model (cm) Actual (m) Model (cm) Actual (m) Model (cm)15 6 23 92 459 1836 11 44 06 24

Table 6 Experimental scheme for dissipation of top coal in coal seams with three soft and complex structures

Horizon Actual Model-ickness (m) Block degree (mm) -ickness (cm) Block degree (mm)

Top coal

Bottom 115 125 46 5Middle-bottom 23 4375 92 175

Middle 185 1875 74 75Middle-top 25 500 10 20

Top 17 250 68 10

Basic roof Bottom 13 300 52 125Top 13 375 52 15

Basic roof Bottom 3637 1000 145 40


(3) Pullout the steel plate above the tail beam of thesupport and the position of the coal discharge port toallow the top coal to fall

(4) Open the bracket window and discharge the top coal(5) While the enthalpy ratio is 1 (the ratio of ver-

miculite weight to the top coal weight above the coaldischarge step) the window is closed

(6) Feed the coal support forward and the shiftingdistance is a feeding distance of the coal miningmachine

(7) Pullout a top-protecting coal plate above the support(two times for one time (6)sim(7) three times for onetime (6)sim(7))

(8) Open the coal opening window to open the coalwhen the yttrium content is 1 (the amount ofvermiculite accounts for the total mass ratio of thetop coal above the step) the window is closed repeatthe process from (6) to (8)

Using the electronic balance to weigh the coal andvermiculite weights the top coal emission rate in the sim-ulation experiment was obtained -e movement andemission patterns of top coal and scattered vermiculite wereobserved during the experiment Analyze the top coal flowand release process in the continuous coal advancement oflow coal placement and the coal waste separation line andflow boundary line in the top and bottom coal Master theshape of the coal gangue flow field under different releasetechnologies

44 Similar Simulation Results

441 Arch during the Top Coal Spill

(1) Form of Arch During the coal laying process due to therandomness of the top coal shape and the relative position ofthe top coal block the diversity of the form of archingoccurs and the arch is composed of coal blocks of soft andhard top coal In the process of coal throwing the archingtypes of coal boring are mainly the arching of the coalopening and the arching of the coal flow above the supporttail beam

(a) Arch opening -e opening of the coal opening isshown in Figure 12 -e front arch foot rests on thetail beam of the support and the rear arch foot fallson the coal flute on the border of the coal flow With

the continuous flow and release of top coal the archexperienced a process of formation expansion anddirect destruction at the same time the shape of thearches the arc angles of the arch lines and theconstant changes in the spans (arch pitches) havealso led to the formation of arches in various formsIn order to reduce the probability of top coalarching the coal should swing as far as possible toincrease the top coal recovery rate and it can also bebroken by arching but this method will damage thescaffold

(b) -e soft and hard coal flows into the arch above thetail boom During the process of coal laying eachlayered top coal continuously shrinks in the di-rection toward the coal discharge port and the softcoal body with the lower string speed and the rel-atively slow hard top coal body are mutuallysqueezed along the interface Friction and unevensinking result in the stress-balanced arch structure-is arch structure is formed at the interface betweensoft and hard top coal As shown in Figure 13 theimpact of the tail beam of the swing support on thearch structure is very small

(2) Arch Probability Experimental studies have shown thatthe probability of arching is the highest in the coal layingprocess when both are used -e probability of laying coaland arching under different coal laying steps is shown inTable 8 At the time of pick and place an average of 043 coalarches were built at a time up to a maximum of 3 -eaverage coal mining and arching were performed twice eachtime which was 465 times that of one mining and onemining-e probability of arching is the lowest among threemining and one casting and the average time for coalarching is 04 each time -e reason is that the span of thearch is large the curvature is small and it is difficult to forma stable arch structure

442 Charge Parameters

(1) One Knife One Falling At the time of one knife one falling(Figure 14) both the vermiculite and the top coal behind thelow-level caving support move toward the coal opening andthe initial coal-bearing boundary line is a quadratic curveTogether with Figure 15 the speed of white and red ganguemigration was greater than that of the middle-upper and

Table 7 Parameters of top coal and direct roof

Horizon -ickness (cm) Weighted volume (cm3each) Sieving length (mm) P (gcm3)Bottom (soft) 46 00301 5 1403Middle-bottom (hard) 92 18182 175 1352Middle (soft) 74 009901 75 1357Middle-top (hard) 10 45333 20 1367Top (soft) 68 04118 10 1354Bottom (white) 52 09667 125 1517Top (red) 52 13333 15 1357Bottom 145 266667 40 1493


middle-low hard top coals before the hard top coal reachedthe coal opening the average recovery rate of hard coal was274 and the average recovery rate of soft coal was 552Soft coal deposits have significantly more coal than hardcoal According to the data the average recovery rate of topcoal is 412 the lowest is 1938 and the highest is 8085but the overall trend is upward -e recovery rate of top coalis far greater than that of thorium and the average level ofgermanium is 36 obviously mixed -e coal deposits inthe top middle and bottom top coal layers are significantlymore than those in the lower upper and middle-upperlayers the amount of coal deposited in the upper-level topcoal is the least

(2) Two Knife One Falling At the time of two knife onefalling the rear end of the support is a mixture of differentpieces of top coal the top coal is difficult to move and theamount of coal reaching the coal opening is small but theamount of coal discharged from the middle lower andmiddle layered top coal is obviously more than the lowerupper middle and top layered coal top coal discharge

(Figure 16) -e starting point of the top coal movement isfarther than that of a mining one and the boundary line ofthe coal mine becomes slower and moves in parallel alongthe direction of advancement of the working face -e av-erage recovery rate of top coal was 9821 which was morethan doubled from one mining experience to another withthe lowest being 5966 and the highest being 18272 -erecovery rate of top coal is far greater than the rate offlooding and the average level of flooding is 11-e rate offlooding is 25 percentage points lower than that of flooding-e average recovery rate of hard coal is 9825 and theaverage recovery rate of soft coal is 9816 -e dischargerate of soft coal is basically the same as that of hard coal SeeFigure 17 for details

(3) ltree Knife One Falling At the time of three knife onefalling the coal-bearing boundary line moved forward butnot smooth along the driving direction of the working face(Figure 18) -e average recovery rate of top coal was8616 the lowest was 5948 and the highest was10904 -e recovery rate of top coal is about two timesthat of the one knife one falling the top coal recovery rateis much higher than the flooding rate the average level ofthe flooding rate is 11 and containing vermiculite rate is25 percentage points lower than that of one knife onefalling and the mix is not obvious -e average recoveryrate of hard coal is 8388 and the average recovery rate ofsoft coal is 8805 -e soft coal discharge rate is basicallythe same as the hard coal emission rate (see Figure 19 fordetails)

In the experiment from seeing the complete discharge ofthe complex top coal the amount of top coal discharged andthe amount of rubble discharged were counted and the ratioof the top coal recovery rate and the rate of containinggermanium to the number of coal deposits during the coalrelease process is shown in Figure 20 During the first 13 coaldeposits the helium-containing rate was kept at or above1 which was caused by manual operation errors Howeverthe overall trend of top coal recovery was reduced and thereduction was large After the thirteenth coal deposit the topcoal recovery rate was stable at between 4 and 11 whilethe indention rate increased

5 Field Application Results and Discussion

51 Working Face Overview N101 face is located in thelower part of the northern mining area the upper part ofwhich is 303 working face (have been mined) the lower partis the unexplored area the east is 102 working face and thewest is the unexcavated area -e elevation of the workingsurface is 520ndash471m the elevation of the ground is 985ndash1043m and the area of the working surface is 94990m2

-e surface coal seam is dominated by bright coal anddark coal with more mirror coal and silk ribbons-e fissureis developed and the structure is complex -e bottom of thecoal seam is 08ndash15m in gray mudstone -e coal quality ispoor and the hardness coefficient is f 16 -e coal seam isstable and is monoclinic with a wavy NE325deg and a coalseam inclination of 17ndash32deg It is 23deg and is close to the

Figure 12 Arch opening

Figure 13 Arch during the flow of soft and hard coal


inclined coal seam Coal seam roof and oor conditions areshown in Table 9 e working face mining method adoptsthe method of moving to the full-scale mining of thelongwall fully mechanized top coal caving method e coalcutting depth is 06m the height of cutting coal is 23m andthe coal laying height is 64m so the ratio of mining to

cutting is 1 278 e coal discharge process adopts theoperation mode of one knife one falling (putting coal in thestep of 06m) and the picking and placing process is carriedout in parallel

52 Mine Pressure Law

521 Line Layout and Observation Method 80m ahead ofthe working face in the upper slot along the side of the workface to play two drill holes arranged in each hole ve KSE-II-1-type drill hole strain gauges drill height is 1m from theoor e layout parameters of drilling and stress gauges inthe working plane are shown in Figure 21

e arrangement of measuring points on the workingsurface is shown in Figure 21 e 70 42 32 and 31brackets are arranged along the inclined direction of theworking face to arrange the stations Each front and rearcolumn is installed with a round chart pressure self-recording device on each diagonal line for continuouscollection of record holders e column cyclic resistancechanges including the initial support force working re-sistance and end-of-cycle resistance of the support

522 Advance Bearing Pressure Size and DistributionWhen drilling the strain gauge the initial pressure is 10MPaAfter two days the changes in the readings of various tableshave stabilized After stabilization the distribution of lateralbearing pressure on the working face formed by roadway

Table 8 Contrast ratio of arching at dierent coal caving distances

Coal caving distance One knife one falling Two knife one falling ree knife one falling

e number of coal arching times each time Maximum 3 6 2Average 043 2 04

(a) (b) (c)

Figure 14 Dump top coal eect of one knife one falling (a) Before relocation (b) After relocation and before coal dumping (c) After layingcoal

Recovery rate of top coalRecovery rate of soft coalRecovery rate of hard coal

0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N

Figure 15 Top coal recovery ratio


digging can be obtained according to the readings of eachtable as shown in Figure 22

From Figure 22 the original rock stress at the measuringpoint is 95MPa the distance from the peak point to theroadway is about 6m the lateral pressure inuence range isabout 9m and the stress concentration factor of the lateralsupport pressure is 141 When the measuring point distanceis about 35m away from the working surface the counts ofindividual tables begin to change indicating that the leadingbearing pressure of the working face will begin to aect thestress at the measuring point

e change in readings of the individual strain gaugesalong the face is shown in Figure 23 From Figure 23 it canbe seen that the peak point of the leading bearing pressure is

about 12m from the working surface and the inuencerange is about 35m e stress concentration factor of theleading bearing pressure is 233

523 Pressure Distribution in the Direction of the InclinedPlane Due to factors such as coal seam inclination miningboundary conditions mining process coal and rock forma-tion conditions and support quality the pressure on thelongwall of the working surface may be dierent Measure-ment and analysis of the pressure distribution of the workingface in the direction of the face during the pressure period andduring the nonpressure period is shown in Figure 24

From Figure 24 we can see the pressure on the topsurface of the work is relatively small during the period ofpressure and during nonadvancement During the pressureperiod the pressure in the middle and lower parts is slightlygreater than the pressure in the middle and upper parts thepressure in the middle and lower parts during the non-pressure period is slightly lower than the pressure in themiddle and upper parts

53TopCoalCavingandRecovery of FullyMechanizedCavingFace Table 10 shows the statistical results of the coalthrowing time of the support before and after the research ofthe project and the thickness of the same coal seam in theN101 fully mechanized top coal caving face e statisticalresults of the coal discharge time show that the eciency ofcoal caving on the face of the project before research is lowand the maximum coal-burning time is more than20minutes On-site observations are mainly due to the highdegree of fragmentation of hard coal in top coal whichresults in large resistance and slow ow Large hard coals areoften blocked on the top of the shield cover beam or the coalopening resulting in the deployment of top coal It is re-ected by the long coal releasing time When the working

(a) (b) (c)

Figure 16 Dump top coal eect of two knife one falling (a) Before relocation (b) After relocation and before coal dumping (c) After layingcoal


2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()

Figure 17 Recovery rates of two knife one falling


face was blasted through a deep hole the released coal wassmall in size and loosely broken e frequency of blockingthe coal opening at the large coal block was signicantlyreduced and the top coal was allowed to settle smoothlywhich represented a shortening of the coal discharge timee release of coal has been improved [40 41]

During the research of the project while continuing toadopt the coal mining and coal mining steps they alsoadopted a series of technical measures to improve the de-ployment of top coal in complex structures Drilling holesare arranged along the two forward slots in the advance faceand then deep-hole blasting is performed to destroy theintegrity of the hard coal in the top coal and cause vibrationcracks to be fully broken en in the gap between thebrackets drills were drilled with a coal-powered electric drill

and the cannons were placed so that the top coal furtherdestroyed the fragmentation and the top coal was ejectede top coal recovery rate at the fully mechanized top coalcaving face has been signicantly improved See Figure 25During the research period of the project the average re-covery rate of the fully mechanized top coal caving face was869 and the maximum recovery rate was 901 e fullymechanized top coal caving face was highly productive andachieved signicant technical and economic benets

6 Conclusion

In this paper based on a comprehensive analysis of thecurrent status of research on thick coal seams with complex

(a) (b) (c)

Figure 18 Dump top coal eect of three knife one falling (a) Before relocation (b) After relocation and before coal dumping (c) Afterlaying coal

Recovery rate of hard coalRecovery rate of soft coalRecovery rate of top coal

2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)

Figure 19 Recovery rates of three knife one falling

Recovery rateGangue rate

0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N

Figure 20 Top coal recovery rates and containing vermiculite rateof three knife one falling


structures at home and abroad theoretical analysis similarlaboratory simulations and numerical simulations are usedto study the rules of the top coal burst in the fully mech-anized top coal caving mining in complex thick coal seams

Table 9 Coal seam roof and bottom conditions on N101 working face

Roof and bottom name Rock name ickness (m) Lithologic characteristics

Basic roof Sandstone 1091 Gray siltstone deep gray mudstone with gray andwhite coarse sand layer

Immediate roof Mudstone coal rock interbedding 157 Grayish white coarse sandstone with dark mudstonemuddy cement loose

False roof Mudstone 107 Dark gray gray-black mudstone with a thin layer ofmudstone in the lower middle

Direct bottom Mudstone 129 Black thick mudstonePrevious bottom Mudstone 49 Gray-black brown-gray mudstone lump

70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support

Stress measurement gauge

Ventilation roadway

Mechanical roadway

Figure 21 Drilling stress measurement point layout and measuring point layout

2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)

4 6 8 10 122Distance from the mechanical roadway (m)

Figure 22 Lateral bearing pressure distribution on working face 2m3m4m5m

6m7m8m

9m10m11m

20 30 40 50 6010Distance from the working face (m)

0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)

Figure 23 Distribution of advance bearing pressure at dierentmeasuring points in boreholes


e coal deposit process parameters were analyzed andstudied Combined with the geology and production tech-nology conditions of the N101 fully mechanized coal miningface in Qinyuan coal mine the eld application and actualmeasurement analysis were performed and the followingmain conclusions were obtained

(1) rough establishing the mechanical model ofbreaking the complex structure it is found that thestrength limit of the hard coal gangue and the coal

body in the top coal body determines the top coalcaving characteristics After the top coal is destroyedby strength the continued destruction of the top coaldepends on the increase of top coal deformationWith the increasing of the thickness of the hard coalgangue in the top coal or the strength of the hardcoal gangue the top coal as a whole gradually ex-hibits the fracture characteristics of medium or hardtop coal As the plastic zone locates in the top controlzone the cumulative displacement of the top coal islow the loose zone is reduced the loose expansionrange formed by the top coal is small the expansiondeformation of the top coal is small the plastic owtime is short and the top coal is poorly discharged Ifthe thickness of the hard coal gangue in the top coalor the strength of the hard coal gangue is reducedthe plastic zone is located in front of the coal wall

(2) rough theoretical analysis the formula for theelastic rupture stress of the hard layer coal ganguemedium reaching the limit state failure is obtainede elastic fracture stress of hard coal gangue in-creases with the increasing of unidirectional com-pressive strength and lateral stress of hard coalgangue e breaking factor formulas of hard coaland soft coal are introduced and the crushing degreeof top coal is described by the size of rupture factore larger the rupture factor is the better thecracking eect of top coal is

End resistance of supports during pressurized periodWeighted resistance of supports during pressurized periodEnd resistance of supports during nonpressurized periodWeighted resistance of supports during pressurized period

0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32

Distribution of the supports

Figure 24 Longitudinal resistance distribution of working face during pressure period and nonpressure period

Table 10 Statistics on the caving time

e caving time of hydraulic support (s)

Maximum time Minimum time beforebeginning of subject

Averagetime Maximum time Minimum time during subject Average time

1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)

Figure 25 Recovery rate of working face during the study period


(3) -rough numerical simulation it is found that withthe decreasing of the thickness or strength of hardcoal gangue in the top coal the peak pressure ofsupport pressure is flat and far away from the coalwall In the midlevel hard coal gangue condition thetop coal below the hard coal gangue is smoothly andquickly released along with the shift frame and themiddle hard layer coal gangue forms the de-lamination the intermediate hard gangue coalgangue breaks insufficiently and the broken lumpsare large Because the lower speed of the hard coalgangue block is slower than that of the top coal it willhinder the top coal body and the top coal above thehard coal gangue will lag behind -erefore the topcoal has poor caving characteristics With the in-creasing of the depth of top coal in different layersthe maximum principal stress also increases and thetop coal is increasingly broken With the increasingof mining depth the top coal plastic zone has be-come larger and the top coal has become moredestructive

(4) -rough similar simulation experiments it wasfound that due to the randomness of the top coalshape and the relative position of the top coal blockin the coal caving process the diversity of the archformation was caused and the arch was composed ofcoal blocks of soft and hard top coal -is phe-nomenon hindered the deployment of top coalExperimental results show that the probability ofarching is greatest in the process of two knife onefalling At the time of one knife one falling an av-erage of 043 coal arches was built at a time up to amaximum of 3 At the time of two knife one fallingan average of 3 coal arches was built at a time whichwas 465 times that of one knife one falling -eprobability of arching is the lowest among two knifeone falling and the average time for coal arching is04 each time -e reason is that the span of the archis large the curvature is small and it is difficult toform a stable arch structure

(5) According to the on-site experiments it was foundthat the top coal recovery rate was the highest whenthe top coal caving step of the complex structure isadopted for two knife one falling mining operationsIn view of the characteristics of top coal crushing infullymechanized coal seams with complex structure acoal mining measure to reduce the fragmentation oftop coal is proposed namely preblasting of top coalby loosening improving the external environment ofthe coal body and hydraulic fracturing of top coal

Data Availability

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

Conflicts of Interest

-e authors declare that they have no conflicts of interest

Authorsrsquo Contributions

Xuelong Li conducted the field measurements and wrote themanuscript All authors gave final approval for publication

Acknowledgments

-is work was supported by the National Science andTechnology Major Project of China (Grant no2016ZX05043005) State Key Research Development Pro-gram of China (Grant no 2016YFC0801404) and NationalNatural Science Foundation of China (Grant no 51674050)which are gratefully acknowledged First of all we would liketo thank Professor Qingting Hu of State Key Laboratory ofCoal Mine Disaster Dynamics and Control he provided uswith some equipment for field measurement Second we aregrateful to Yongjiang Luo who provided comments thatsubstantially improved the manuscript

References

[1] X Liu D Song X He Z Wang M Zeng and K ZengldquoNanopore structure of deep-burial coals explored by AFMrdquoFuel vol 246 pp 9ndash17 2019

[2] G Si S Jamnikar J Lazar et al ldquoMonitoring and modellingof gas dynamics in multi-level longwall top coal caving ofultra-thick coal seams part I borehole measurements and aconceptual model for gas emission zonesrdquo InternationalJournal of Coal Geology vol 144-145 pp 98ndash110 2015

[3] E Y Wang X F Liu X Q He and Z H Li ldquoAcousticemission and electromagnetic radiation synchronized mon-itoring technology and early-warning application for coal androck dynamic disasterrdquo Journal of China University of Miningand Technology vol 47 no 5 pp 953ndash959 2018

[4] Q Zou and B Lin ldquoFluid-solid coupling characteristics of gas-bearing coal subjected to hydraulic slotting an experimentalinvestigationrdquo Energy and Fuels vol 32 no 2 pp 1047ndash10602018

[5] L Q Duan L Dong and L J Ma ldquoExperimental study ofacoustic emission characteristics of foamed concrete underuniaxial compressionrdquo Journal of China University of Miningand Technology vol 47 no 4 pp 742ndash747 2018

[6] S-h Tu Y Yong Y Zhen X-t Ma and W Qi ldquoResearchsituation and prospect of fully mechanized mining technologyin thick coal seams in Chinardquo Procedia Earth and PlanetaryScience vol 1 no 1 pp 35ndash40 2009

[7] J Wang ldquoDevelopment and prospect on fully mechanizedmining in Chinese coal minesrdquo International Journal of CoalScience and Technology vol 1 no 3 pp 253ndash260 2014

[8] J Xu N Wang and Y Wang ldquoMulti-pyramid image spatialstructure based on coarse-to-fine pyramid and scale spacerdquoCAAI Transactions on Intelligence Technology vol 3 no 4pp 228ndash234 2018

[9] H Alehossein and B A Poulsen ldquoStress analysis of longwalltop coal cavingrdquo International Journal of Rock Mechanics andMining Sciences vol 47 no 1 pp 30ndash41 2010

[10] X Li E Wang Z Li Z Liu D Song and L Qiu ldquoRock burstmonitoring by integrated microseismic and electromagneticradiation methodsrdquo Rock Mechanics and Rock Engineeringvol 49 no 11 pp 4393ndash4406 2016

[11] X Li Z Li E Wang et al ldquoPattern Recognition of MineMicroseismic and Blasting Events Based on Wave FractalFeaturesrdquo Fractals vol 26 no 3 article 1850029 2018


[12] L Yu S H Yan H Y Yu and Z Zhang ldquoStudying of dy-namic bear characteristics and adaptability of support in topcoal caving with great mining heightrdquo Procedia Engineeringvol 26 pp 640ndash646 2011

[13] D Szurgacz and J Brodny ldquoDynamic tests of a leg in apowered roof support equipped with an innovative hydraulicsystemrdquo E3S Web of Conferences vol 41 p 03019 2018

[14] D Szurgacz and J Brodny ldquoAnalysis of rock mass dynamicimpact influence on the operation of a powered roof supportcontrol systemrdquo E3S Web of Conferences vol 29 p 000062018

[15] D Szurgacz and J Brodny ldquoAnalysis of load of a powered roofsupportrsquos hydraulic legrdquo E3S Web of Conferences vol 71p 00002 2018

[16] W Guo Y Tan and E Bai ldquoTop coal caving mining tech-nique in thick coal seam beneath the earth damrdquo InternationalJournal of Mining Science and Technology vol 27 no 1pp 165ndash170 2017

[17] X R Bai and J M Li Modern Caving Mining lteories andPractical Technology China University of Mining Techonol-ogy Press Xuzhou China 2001

[18] J Zhang Z Zhao and Y Gao ldquoResearch on top coal cavingtechnique in steep and extra-thick coal seamrdquo Procedia Earthand Planetary Science vol 2 pp 145ndash149 2011

[19] J Wang and Z Wang ldquoSystematic principles of surroundingrock control in longwall mining within thick coal seamsrdquoInternational Journal of Mining Science and Technologyvol 29 no 1 pp 65ndash71 2019

[20] D W Mckee S J Clement J Almutairi and J Xu ldquoSurvey ofadvances and challenges in intelligent autonomy for dis-tributed cyber-physical systemsrdquo CAAI Transactions on In-telligence Technology vol 3 no 2 pp 75ndash82 2018

[21] S J Xu X P Lai and F Cui ldquoTop coal flows in an excavationdisturbed zone of high section top coal caving of an extremelysteep and thick seamrdquoMining Science and Technology vol 21no 1 pp 99ndash105 2011

[22] S Yang J Zhang Y Chen and Z Song ldquoEffect of upwardangle on the drawing mechanism in longwall top-coal cavingminingrdquo International Journal of Rock Mechanics and MiningSciences vol 85 pp 92ndash101 2016

[23] R Singh and T N Singh ldquoInvestigation into the behaviour ofa support system and roof strata during sublevel caving of athick coal seamrdquo Geotechnical and Geological Engineeringvol 17 no 1 pp 21ndash35 1999

[24] N E Yasitli and B Unver ldquo3-D numerical modelling ofstresses around a longwall panel with top coal cavingrdquo Journalof the Southern African Institute of Mining and Metallurgyvol 105 no 5 pp 287ndash300 2005

[25] H Xie and H W Zhou ldquoApplication of fractal theory to top-coal cavingrdquo Chaos Solitons and Fractals vol 36 no 4pp 797ndash807 2008

[26] W-l Shen J-b Bai W-f Li and X-y Wang ldquoPrediction ofrelative displacement for entry roof with weak plane under theeffect of mining abutment stressrdquo Tunnelling and Un-derground Space Technology vol 71 pp 309ndash317 2018

[27] WWang G Zhao G Lou and S Wang ldquoHeight of fracturedzone inside overlying strata under high-intensity mining inChinardquo International Journal of Mining Science and Tech-nology vol 29 no 1 pp 45ndash49 2019

[28] B Kong Z Li E Wang W Lu L Chen and G Lu ldquoex-perimental study for characterization the process of coaloxidation and spontaneous combustion by electromagneticradiation techniquerdquo Process Safety and EnvironmentalProtection vol 119 pp 285ndash294 2018

[29] G Cheng T Ma C Tang H Liu and S Wang ldquoA zoningmodel for coal mining-induced strata movement based onmicroseismic monitoringrdquo International Journal of RockMechanics and Mining Sciences vol 94 pp 123ndash138 2017

[30] R S Yang Y L Zhu X L Zhu D M Guo and G H LildquoDiscussions on some security mining problems of fully-mechanized top coal mining in ldquothree softrdquo large inclinedangle working facerdquo Procedia Engineering vol 26pp 1144ndash1149 2011

[31] X Z Xie and T L Zhao ldquoAnalysis on the top-coal cavingstructure of extra-thick hard coal seam with shallow depth infully mechanized sublevel caving miningrdquo Journal of ChinaCoal Society vol 41 no 2 pp 359ndash366 2016

[32] N Zhang and C Liu ldquoArch structure effect of the coal gangueflow of the fully mechanized caving in special thick coal seamand its impact on the loss of top coalrdquo International Journal ofMining Science and Technology vol 26 no 4 pp 593ndash5992016

[33] X Kong E Wang S Hu R Shen X Li and T Shen ldquoFractalcharacteristics and acoustic emission of coal containingmethane in triaxial compression failurerdquo Journal of Appliedgeophysics vol 124 pp 139ndash147 2016

[34] B Hakan O Ferid and A Osman ldquoPrediction of the stressesaround main and tail gates during top coal caving by 3Dnumerical analysisrdquo International Journal of Rock Mechanicsand Mining Sciences vol 76 pp 88ndash97 2015

[35] D Yun Z Liu W Cheng Z Fan D Wang and Y ZhangldquoMonitoring strata behavior due to multi-slicing top coalcaving longwall mining in steeply dipping extra thick coalseamrdquo International Journal of Mining Science and Technol-ogy vol 27 no 1 pp 179ndash184 2017

[36] A Vakili and B K Hebblewhite ldquoA new cavability assessmentcriterion for longwall top coal cavingrdquo International Journalof Rock Mechanics and Mining Sciences vol 47 no 8pp 1317ndash1329 2010

[37] S J Feng S G Sun Y G Lv and J Lv ldquoResearch on theheight of water flowing fractured zone of fully mechanizedcaving mining in extra-thick coal seamrdquo Procedia Engineer-ing vol 26 pp 466ndash471 2011

[38] Z H Chen H P Xie and Z M Lin ldquoStudy on falling abilityof top coal during top coal caving by damage mechanicsrdquoChinese Journal of Rock Mechanics and Engineering vol 21no 8 pp 1136ndash1140 2002

[39] W J Wang C Q Zhu and R Q Xiong ldquoAn artificial neuralnetwork for distinguishing the difficulty degree of roof coalcaving of steep seamrdquo Journal of China Coal Society vol 27no 2 pp 134ndash138 2002

[40] J Wang B Yu H Kang et al ldquoKey technologies andequipment for a fully mechanized top-coal caving operationwith a large mining height at ultra-thick coal seamsrdquo In-ternational Journal of Coal Science and Technology vol 2no 2 pp 97ndash161 2015

[41] B Jiang ldquoBehaviors of overlying strata in extra-thick coalseams using top-coal caving methodrdquo Journal of Rock Me-chanics and Geotechnical Engineering vol 8 no 2 pp 238ndash247 2016


International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

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Hindawiwwwhindawicom Volume 2018


Active and Passive Electronic Components

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

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Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawiwwwhindawicom

Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Control Scienceand Engineering

Journal of



Journal ofEngineeringVolume 2018

SensorsJournal of



RotatingMachinery


Modelling ampSimulationin EngineeringHindawiwwwhindawicom Volume 2018


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation


Hindawi

wwwhindawicom Volume 2018

Advances in

Multimedia

Submit your manuscripts atwwwhindawicom

affecting roof-coal caving including the uniaxial compres-sive strength (σc) the thickness of coal seam the develop-ment of joint fractures in coal seam etc

-e strength of coal seam mainly reflects the self-abilityto resist damage which determines the fragmentation de-gree of roof-coal under the action of mining stope pressureAnd the fragmentation degree of roof-coal will directly affectthe roof-coal recovery During the extraction of hard coaldue to that the mining stope pressure cannot effectivelyfragment the roof-coal the roof-coal blocks are too large toreach the requirement of top coal caving which will reducethe roof-coal recovery [27ndash30]

-in top coal is a pseudo-top and it is difficult to controlit from falling in the tail of the bracket which will lead todirect crushing ahead of the top it would mix with the topcoal when released to the coal outlet through which not onlythe coal quality will be affected but also a large number of topcoal will be lost in the goaf overthick top coal is hard to befully loose in the top control area so it is difficult to fall in thefalling area In particular with the gradual increase in thethickness of coal seams being exploited the mine pressure inthe fully mechanized subsidence stope is becoming moreintense Whether the large-scale top coal body can bebroken fallen or released under the action of mine pressurethe height of the fully mechanized top coal caving face can beachieved -e production rate has become a key technicalproblem that restricts the use of fully mechanized sublevelcaving mining in extremely thick coal seams and even thickcoal seams [19 31ndash33]

According to on-site observations the weakest surface ofthe coal affected by top coal caving in fully mechanized topcoal caving face is the joints bedding and fractures of coalObviously coal seams with joints and fissures developed havepoor integrity of the coal body and the overall strength isreduced -e top coal is easily broken under the influence ofsupporting pressure At the same time the more dense thefissures are the more easily the top coal is broken and thesmaller the degree of eruption is the more favorable it is torelease that is the better the release of top coal and vice versa[33ndash35] In addition the top coal caving is also related to theperiod of the roof the depth of the coal seam the hardness ofthe coal seam the amount of sand and the filling factor

In recent years with the development of science andtechnology more and more advanced technological methodshave been introduced into the research of fully mechanizedcaving mining [36] Especially in the aspect of evaluationmany advanced calculation theories and methods are grad-ually introduced into the top coal evaluation For example thegray-fuzzy evaluation method is used to study that the steepseam coal can be relegated and fuzzy mathematics theory isused to classify the caving of top coal under different coalseam conditions [37] Chen et al [38] used the basic conceptsof damage mechanics to describe the relationship betweendamage and release of top coal Wang et al [39] used theartificial intelligence as a reference to establish an artificialneural network process of top coal disruptive identification insteep-inclined coal caving roof caving-e above new theoriesand methods not only have their own characteristics but alsohave their certain deficiencies For example the fuzzy

comprehensive evaluation method often requires certainsubjectivity and randomness when determining the degree ofmembership and giving different weight to each index -eartificial neural network method has some shortcomings inslowing convergence rate easy falling into local optimum andhidden layer determination with subjectivity Support vectormachine to determine the boundary anti-interference abilityis poor and sensitive to noise data To this end we also need toexplore a more scientific and effective evaluation method oftop coal emission -e factors influencing the runoff of topcoal are complex diverse and nonlinear so it is hard to comeup with accurate and general discriminant criteria

At present fully mechanized top coal caving mining canbe applied to coal seams with better geological conditionsDuring the fully mechanized top coal caving mining ofcomplex structure thick coal seams due to the presence ofentrainment and hard coal coal seams often have largefracture fragments difficult top coal release and poor topcoal deployment In order to study the law of breakingreleasing and destabilization of top coal with complexstructures this paper selects the representative geology andproduction conditions of Qinyuan coal mine in Baoji cityChina Adopting the method of combining theoreticalanalysis laboratory simulation and numerical simulationroof breaking and releasing rules of top coal and technicalparameters of caving in fully mechanized top coal cavingmining with complex structure and thick coal seam thefollowing studies are conducted

(1) -e research results of predecessors are combinedand the breaking characteristics of top coal in fullymechanized caving mining with thick seam ofcomplicated structure are analyzed In terms of theactual stress conditions of hard coal gangue in thefully mechanized top coal cavingmining the stabilityof the hard coal gangue (the hard coal delaminationor the gangue in the top coal body) is studied themechanical model of the corresponding hardenedcoal gangue is established Based on this thecrushing effect of the hardened coal gangue and thetop coal caving are analyzed

(2) -e law of breaking and instability of top coal in fullymechanized top coal caving mining with compli-cated structure and thick seam is analyzed y meansof discrete element numerical simulation methodstress field displacement field and distributioncharacter of the failure field are analyzed emphati-cally -e crushing effect of top coal and the top coaldischarge are analyzed -e law of breaking anddestabilization of top coal in fully mechanized topcoal caving mining with complicated structure isobtained

(3) -e simulation of laboratory bulk as a researchmethod is performed and the technical parametersof fully mechanized caving mining with thick coalseam with complex structure are studied Analyzethe coal gangue emanation form and top coal fallingin the process of arching and reach the complexstructure of the law of the top coal emission And put










K 1

1Kc( 1113857 + 1Km( 1113857

Kc middot Km

Kc + Km (1)

-en




-at isΔSmΔS

Kc

Kc + Km

KcKm( 1113857

KcKm( 1113857 + 1 (3)






ε3 1E

σ3 minus μ σ1 minus σ2( 11138571113858 1113859 (4)

If σ2 σ3 then

ε3 1E

(1minus μ)σ3 minus μσ11113858 1113859 (5)


σcE

(6)


minusμσ3E

1E

(1minus μ)σ3 minus μσ11113858 1113859 (7)



σ3 (8)


σ1 σc 1μminus 11113888 1113889σ3 (9)










i KcH

σc

iprime KcH

σcprime

(11)


1

F

F

2




















q sum ch 13MPa (12)



0 10 20 30 40 50 60

06

07

08

09

10

11

12

13Fr

actu

re co

effic

ient

of h

ard

coal

(i)

σc (MPa)

R2 = 096755

(a)

σc (MPa)0 2 4 6 8 10

4

6

8

10

12

14

Frac

ture

coef

ficie

nt o

f sof

t coa

l (iprime)

R2 = 099926

(b)




Bulk modulusK (GPa)



AdhesionC (MPa)





















0

5

10

15

20

25

30

35

40

Vert

ical

stre

ss (M

Pa)









TopMiddleBottom

ndash6

ndash4

ndash2

0

2

4

6

8Sh

earin

g str

engt

h (M

Pa)


(a)

TopMiddleBottom

ndash4

ndash3

ndash2

ndash1

0

1

2

Reco

very

rate

()


(b)


TopMiddleBottom

ndash5

0

5

10

15

20

25

30

35

40

Diff

eren

ce b

etw

een

the m

axim

um p

rinci

pal

stres

s and

the m

inim

um p

rinci

pal s

tress

(MPa

)








H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss


(a)

H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss (M

Pa)


(b)


Vert

ical

disp

lace

men

t (m

m)



150

0

50

100

200

250

300

350

400


Vert

ical

disp

lace

men

t (m

m)

MiddleBottom


200

0

100

300

400

500








Ver

tical

disp

lace

men

t (m

m)

H = 320mH = 520mH = 720m


0

200

400

600

800

1000

(a)

H = 320mH = 520mH = 720m

Ver

tical

disp

lace

men

t (m

m)


0

200

400

600

800

1000

(b)



Sandstone

Mudstoneand coal

Mudstone

Coal

Sandymudstone

Mudstone

(a) (b)

157

107

129

49

1091

95

Coal seam

17

25

185

23

115

Hardness

Soft

Hard

Soft

Hard

Soft









Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6










Top coal



Top 17 250 68 10











































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia










K 1

1Kc( 1113857 + 1Km( 1113857

Kc middot Km

Kc + Km (1)

-en




-at isΔSmΔS

Kc

Kc + Km

KcKm( 1113857

KcKm( 1113857 + 1 (3)






ε3 1E

σ3 minus μ σ1 minus σ2( 11138571113858 1113859 (4)

If σ2 σ3 then

ε3 1E

(1minus μ)σ3 minus μσ11113858 1113859 (5)


σcE

(6)


minusμσ3E

1E

(1minus μ)σ3 minus μσ11113858 1113859 (7)



σ3 (8)


σ1 σc 1μminus 11113888 1113889σ3 (9)










i KcH

σc

iprime KcH

σcprime

(11)


1

F

F

2




















q sum ch 13MPa (12)



0 10 20 30 40 50 60

06

07

08

09

10

11

12

13Fr

actu

re co

effic

ient

of h

ard

coal

(i)

σc (MPa)

R2 = 096755

(a)

σc (MPa)0 2 4 6 8 10

4

6

8

10

12

14

Frac

ture

coef

ficie

nt o

f sof

t coa

l (iprime)

R2 = 099926

(b)




Bulk modulusK (GPa)



AdhesionC (MPa)





















0

5

10

15

20

25

30

35

40

Vert

ical

stre

ss (M

Pa)









TopMiddleBottom

ndash6

ndash4

ndash2

0

2

4

6

8Sh

earin

g str

engt

h (M

Pa)


(a)

TopMiddleBottom

ndash4

ndash3

ndash2

ndash1

0

1

2

Reco

very

rate

()


(b)


TopMiddleBottom

ndash5

0

5

10

15

20

25

30

35

40

Diff

eren

ce b

etw

een

the m

axim

um p

rinci

pal

stres

s and

the m

inim

um p

rinci

pal s

tress

(MPa

)








H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss


(a)

H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss (M

Pa)


(b)


Vert

ical

disp

lace

men

t (m

m)



150

0

50

100

200

250

300

350

400


Vert

ical

disp

lace

men

t (m

m)

MiddleBottom


200

0

100

300

400

500








Ver

tical

disp

lace

men

t (m

m)

H = 320mH = 520mH = 720m


0

200

400

600

800

1000

(a)

H = 320mH = 520mH = 720m

Ver

tical

disp

lace

men

t (m

m)


0

200

400

600

800

1000

(b)



Sandstone

Mudstoneand coal

Mudstone

Coal

Sandymudstone

Mudstone

(a) (b)

157

107

129

49

1091

95

Coal seam

17

25

185

23

115

Hardness

Soft

Hard

Soft

Hard

Soft









Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6










Top coal



Top 17 250 68 10











































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





ε3 1E

σ3 minus μ σ1 minus σ2( 11138571113858 1113859 (4)

If σ2 σ3 then

ε3 1E

(1minus μ)σ3 minus μσ11113858 1113859 (5)


σcE

(6)


minusμσ3E

1E

(1minus μ)σ3 minus μσ11113858 1113859 (7)



σ3 (8)


σ1 σc 1μminus 11113888 1113889σ3 (9)










i KcH

σc

iprime KcH

σcprime

(11)


1

F

F

2




















q sum ch 13MPa (12)



0 10 20 30 40 50 60

06

07

08

09

10

11

12

13Fr

actu

re co

effic

ient

of h

ard

coal

(i)

σc (MPa)

R2 = 096755

(a)

σc (MPa)0 2 4 6 8 10

4

6

8

10

12

14

Frac

ture

coef

ficie

nt o

f sof

t coa

l (iprime)

R2 = 099926

(b)




Bulk modulusK (GPa)



AdhesionC (MPa)





















0

5

10

15

20

25

30

35

40

Vert

ical

stre

ss (M

Pa)









TopMiddleBottom

ndash6

ndash4

ndash2

0

2

4

6

8Sh

earin

g str

engt

h (M

Pa)


(a)

TopMiddleBottom

ndash4

ndash3

ndash2

ndash1

0

1

2

Reco

very

rate

()


(b)


TopMiddleBottom

ndash5

0

5

10

15

20

25

30

35

40

Diff

eren

ce b

etw

een

the m

axim

um p

rinci

pal

stres

s and

the m

inim

um p

rinci

pal s

tress

(MPa

)








H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss


(a)

H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss (M

Pa)


(b)


Vert

ical

disp

lace

men

t (m

m)



150

0

50

100

200

250

300

350

400


Vert

ical

disp

lace

men

t (m

m)

MiddleBottom


200

0

100

300

400

500








Ver

tical

disp

lace

men

t (m

m)

H = 320mH = 520mH = 720m


0

200

400

600

800

1000

(a)

H = 320mH = 520mH = 720m

Ver

tical

disp

lace

men

t (m

m)


0

200

400

600

800

1000

(b)



Sandstone

Mudstoneand coal

Mudstone

Coal

Sandymudstone

Mudstone

(a) (b)

157

107

129

49

1091

95

Coal seam

17

25

185

23

115

Hardness

Soft

Hard

Soft

Hard

Soft









Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6










Top coal



Top 17 250 68 10











































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



















q sum ch 13MPa (12)



0 10 20 30 40 50 60

06

07

08

09

10

11

12

13Fr

actu

re co

effic

ient

of h

ard

coal

(i)

σc (MPa)

R2 = 096755

(a)

σc (MPa)0 2 4 6 8 10

4

6

8

10

12

14

Frac

ture

coef

ficie

nt o

f sof

t coa

l (iprime)

R2 = 099926

(b)




Bulk modulusK (GPa)



AdhesionC (MPa)





















0

5

10

15

20

25

30

35

40

Vert

ical

stre

ss (M

Pa)









TopMiddleBottom

ndash6

ndash4

ndash2

0

2

4

6

8Sh

earin

g str

engt

h (M

Pa)


(a)

TopMiddleBottom

ndash4

ndash3

ndash2

ndash1

0

1

2

Reco

very

rate

()


(b)


TopMiddleBottom

ndash5

0

5

10

15

20

25

30

35

40

Diff

eren

ce b

etw

een

the m

axim

um p

rinci

pal

stres

s and

the m

inim

um p

rinci

pal s

tress

(MPa

)








H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss


(a)

H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss (M

Pa)


(b)


Vert

ical

disp

lace

men

t (m

m)



150

0

50

100

200

250

300

350

400


Vert

ical

disp

lace

men

t (m

m)

MiddleBottom


200

0

100

300

400

500








Ver

tical

disp

lace

men

t (m

m)

H = 320mH = 520mH = 720m


0

200

400

600

800

1000

(a)

H = 320mH = 520mH = 720m

Ver

tical

disp

lace

men

t (m

m)


0

200

400

600

800

1000

(b)



Sandstone

Mudstoneand coal

Mudstone

Coal

Sandymudstone

Mudstone

(a) (b)

157

107

129

49

1091

95

Coal seam

17

25

185

23

115

Hardness

Soft

Hard

Soft

Hard

Soft









Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6










Top coal



Top 17 250 68 10











































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia












0

5

10

15

20

25

30

35

40

Vert

ical

stre

ss (M

Pa)









TopMiddleBottom

ndash6

ndash4

ndash2

0

2

4

6

8Sh

earin

g str

engt

h (M

Pa)


(a)

TopMiddleBottom

ndash4

ndash3

ndash2

ndash1

0

1

2

Reco

very

rate

()


(b)


TopMiddleBottom

ndash5

0

5

10

15

20

25

30

35

40

Diff

eren

ce b

etw

een

the m

axim

um p

rinci

pal

stres

s and

the m

inim

um p

rinci

pal s

tress

(MPa

)








H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss


(a)

H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss (M

Pa)


(b)


Vert

ical

disp

lace

men

t (m

m)



150

0

50

100

200

250

300

350

400


Vert

ical

disp

lace

men

t (m

m)

MiddleBottom


200

0

100

300

400

500








Ver

tical

disp

lace

men

t (m

m)

H = 320mH = 520mH = 720m


0

200

400

600

800

1000

(a)

H = 320mH = 520mH = 720m

Ver

tical

disp

lace

men

t (m

m)


0

200

400

600

800

1000

(b)



Sandstone

Mudstoneand coal

Mudstone

Coal

Sandymudstone

Mudstone

(a) (b)

157

107

129

49

1091

95

Coal seam

17

25

185

23

115

Hardness

Soft

Hard

Soft

Hard

Soft









Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6










Top coal



Top 17 250 68 10











































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia







TopMiddleBottom

ndash6

ndash4

ndash2

0

2

4

6

8Sh

earin

g str

engt

h (M

Pa)


(a)

TopMiddleBottom

ndash4

ndash3

ndash2

ndash1

0

1

2

Reco

very

rate

()


(b)


TopMiddleBottom

ndash5

0

5

10

15

20

25

30

35

40

Diff

eren

ce b

etw

een

the m

axim

um p

rinci

pal

stres

s and

the m

inim

um p

rinci

pal s

tress

(MPa

)








H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss


(a)

H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss (M

Pa)


(b)


Vert

ical

disp

lace

men

t (m

m)



150

0

50

100

200

250

300

350

400


Vert

ical

disp

lace

men

t (m

m)

MiddleBottom


200

0

100

300

400

500








Ver

tical

disp

lace

men

t (m

m)

H = 320mH = 520mH = 720m


0

200

400

600

800

1000

(a)

H = 320mH = 520mH = 720m

Ver

tical

disp

lace

men

t (m

m)


0

200

400

600

800

1000

(b)



Sandstone

Mudstoneand coal

Mudstone

Coal

Sandymudstone

Mudstone

(a) (b)

157

107

129

49

1091

95

Coal seam

17

25

185

23

115

Hardness

Soft

Hard

Soft

Hard

Soft









Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6










Top coal



Top 17 250 68 10











































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia






H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss


(a)

H = 320mH = 520mH = 720m

0

10

20

30

40

50

Max

imum

prin

cipa

l stre

ss (M

Pa)


(b)


Vert

ical

disp

lace

men

t (m

m)



150

0

50

100

200

250

300

350

400


Vert

ical

disp

lace

men

t (m

m)

MiddleBottom


200

0

100

300

400

500








Ver

tical

disp

lace

men

t (m

m)

H = 320mH = 520mH = 720m


0

200

400

600

800

1000

(a)

H = 320mH = 520mH = 720m

Ver

tical

disp

lace

men

t (m

m)


0

200

400

600

800

1000

(b)



Sandstone

Mudstoneand coal

Mudstone

Coal

Sandymudstone

Mudstone

(a) (b)

157

107

129

49

1091

95

Coal seam

17

25

185

23

115

Hardness

Soft

Hard

Soft

Hard

Soft









Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6










Top coal



Top 17 250 68 10











































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia







Ver

tical

disp

lace

men

t (m

m)

H = 320mH = 520mH = 720m


0

200

400

600

800

1000

(a)

H = 320mH = 520mH = 720m

Ver

tical

disp

lace

men

t (m

m)


0

200

400

600

800

1000

(b)



Sandstone

Mudstoneand coal

Mudstone

Coal

Sandymudstone

Mudstone

(a) (b)

157

107

129

49

1091

95

Coal seam

17

25

185

23

115

Hardness

Soft

Hard

Soft

Hard

Soft









Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6










Top coal



Top 17 250 68 10











































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia








Measuringpoint 2

Measuringpoint 3

Measuringpoint 4

Measuringpoint 5

Measuringpoint 6










Top coal



Top 17 250 68 10











































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia









































(a) (b) (c)



0

10

20

30

40

50

60

70

80

90

Reco

very

rate

()

2 3 4 5 6 7 81Times N










(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia









(a) (b) (c)



2 3 4 5 6 71Times N

40

60

80

100

120

140

160

180

200

220

Reco

very

rate

()






6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





6 Conclusion


(a) (b) (c)



2 3 4 51Times N

50

60

70

80

90

100

110

120

Reco

very

rate

(rat

e)



0

20

40

60

80

100

120

140

160

180

Perc

ent

15 20 255 100Times N










70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia









70

42

32

31

12m

54m 69

m

80m

2m3m 2m

2m

2m

Working face

Hydralic support


Ventilation roadway

Mechanical roadway


2

4

6

8

10

12

14

Supp

ort p

ress

ure (

MPa

)



6m7m8m

9m10m11m


0

5

10

15

20

25

Supp

ort p

ress

ure (

MPa

)








0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia







0

1000

2000

3000

4000

5000

6000

7000

Supp

ort r

esist

ance

(kN

)

41 3170 32







1286 197 742 312 48 180

78

80

82

84

86

88

90

92

Reco

very

rate

()

2 4 6 8 10 120

Time (month)






Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





Data Availability






Acknowledgments


References














































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


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