Table of Content

15 May 2015, Volume 32 Issue 3

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Tremor mechanism and disaster control during repeated mining

JIANG Fuxing, YAO Shunli, WEI Quande, WANG Fuqi, HAO Yingge, WANG Yingde, FENG Yu

2015, 32(3):  349-355. 

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The instability of super-thick strata will induce tremors with large energies during repeated mining．Based on this phenomenon, the caving and movement rules of overlying strata during repeated mining were analysed, the structural form of key block in the super-thick strata as well as the stress situation and fracturing instability characteristics in different areas were further studied．Finally, the tremor mechanism induced by repeated mining was obtained．That is, first, the increase of mining height activates the gob strata, and leads to sliding or shearing instability of the hinged balance structure in roof strata, thus triggering the occurrence of mining-induced tremors．Second, the external expansion of strata movement line enlarges the horizontal and vertical move ranges of roof strata on the border areas, which results in the large-scale instability of the super-thick strata in the highly-concentrated stress area and then in terms of rock burst mechanism induced by tremor, the optimization of working face design, disturbance reduction to dangerous zones and structural strength enhancement of roadway surrounding rock were carried out to effectively ensure the mining safety in the protected face, and achieved the control goal of tremor occurred with rock burst disaster-free.

Feasibility analysis of grouting reinforcement of Ordovician top in Feicheng coalfield

SHI Longqing, QIU Mei, NIU Chao, HAN Jin, JI Xiaokai

2015, 32(3):  356-362. 

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In view that drainage for decreasing water pressure was useless to guarantee safe mining threatened by water inrush from Ordovician limestone in Feicheng coalfield, the feasibility study of grouting reinforcement of Ordovician top was carried out．Based on the statistics of exploratory boring data, coal mine drilling construction, X-ray diffraction of limestone samples, and microscopic thin section analysis, the macro and micro characteristics of Karst fissure in the Ordovician top of Feicheng coalfield were obtained．The result shows that the optimal depth for grouting reconstruction in Feicheng coalfield is about 20 meters below Ordovician top．Taking LW101002 in Caozhuang coal mine as test object, the grouting reinforcement project for Ordovician top was carried out．The conclusion validity is proved by the comparison of geophysical exploration and drilling before and after grouting．Practice proves that safety mining on the aquifer with high-pressure can be achieved by grouting reinforcement of Ordovician top.

The impermeability of limestone aquifuge in bottom coal seam floor and its application in Xinji Second Coal Mine

BAI Haibo, RONG Huren, YANG Cheng, WEI Xiaoqi, WANG Yanmeng, CHEN Yaojie

2015, 32(3):  363-368. 

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Limestone layer is often regarded as the main cause of coal mine water damage and water inrush events, which actually happened more than once in old mining area in Huainan. A conception has been put forward that reconstruction or direct utility of relative impermeability of floor limestone layer can solve the problem of high water pressure and thin aquiclude and ensure safety during mining under pressure. Xinji Second coal mine has been selected as the research field which is located in the southern edge of the midwest coalfields and comprehensive methods have been used to research including the index test of rock composition, chemical action of compositions of groundwater, and rock mechanic, micro-pore structure, the laboratory experiment about permeability and the field test about hydrogeologic drilling, geophysical prospecting. The research results show that: 1) Xinji Second Coal Mine is cut by faults all around, with the top covered by quaternary system and metamorphic nappe. The in-situ stress changes from tensile in the shallow part to compressive at a depth under 500 m. The crack of deep rock layer is not easy to open up. 2) The hydrochemical type is Cl-Na. Salinity is greater than 1.5 g/L and rock voids is filled by the precipitation. 3) The permeability and water rich property of limestone floor is poor, so it can be regarded as aquiclude. It is confirmed that inrush boreholes mostly close to the large faults and water yield is small and disappear quickly through boreholes in the coal mine. Safe mining of the first coal mining face and safety tunneling of the second working face testify the result that the floor limestone layer is aquiclude and the water-resisting key strata after reconstruct is correct.

Coal pillar stability and surface movement characteristics of deep wide strip pillar mining

GUO Weijia, WANG Hailong, LIU Zengping

2015, 32(3):  369-375. 

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Coal pillar stability and surface movement characteristics of wide strip pillar mining in deep mine have been researched by using field measurement, three-dimensional similar material simulation, numerical simulation and theoretical analysis. Researches show that under the mining conditions of deep mine, the width of plastic zone becomes larger significantly and load bearing above the whole coal pillar in deep mine is saddle-shaped; The lateral deformation is discontinuous, stepped and mutational, which is focused on the edge 9.5 m away from the coal wall. With the diminution of coal pillar’s width, the width of plastic zone increases notably. In addition, surface subsidence reaches extremum under this geological and mining condition in group strip coal pillar mining. The subsidence basin is larger but gentler and uniform. The subsidence coefficient is 0.22 and the movement and deformation is continuous and long-term. Outer edge of subsidence basin appears surface rebound. Based on the characteristics of deep wide strip pillar mining, the dimensional design method has been put forward．

BOTDA distributed measurement and analysis of mining overburden separation

PIAO Chunde, SHI Bin, WEI Guangqing, YU Lin, CHEN Enyu

2015, 32(3):  376-381. 

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In view of underground coal mining and stratigraphic features in Yangliu Coal Mine, by using BOTDA fiber-optic sensing technology, the distributed monitoring methods of overburden deformation were studied, the mining-induced deformation characteristics of overlying strata were analyzed, and the separation mechanism was further explored The results show that before the coal face passing through the vertical line of monitoring hole, as the coal face gets closer to monitoring hole, overlying strata pressure becomes more obviously, stress variation is greater, and the strata behavior ranges from the top deformation zone of overlying strata to the upper stable hard rock. After coal face passing through the monitoring hole, the bed separation appears gradually inside overlying strata, where the tensile stress value steadily increases, and the stress value is related to the thickness of stable hard rock, mechanical properties, mining range, and the distance to seam roof, etc. Distributed monitoring results basically tally with the theoretical calculations．

Stress distribution characteristics of deep mine in fully-mechanized sublevel caving face based on microseismic and online stress monitoring system

WANG Dechao, WANG Qi, LI Shucai, WANG Fuqi, GUO Nianbo, WANG Baoqi, CHENG Xiangbo, PAN Rui

2015, 32(3):  382-388. 

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In order to study the characteristics of the deep shaft full-mechanized caving mining abutment pressure distribution, field measurement focusing on vertical stress has been carried out by using microseismic and online stress monitoring system at 1306 working face in Zhaolou mine．The research shows that the process of workface extracting can be divided into three stages: initial mining stage, “square stage” and normal mining stage. Advanced abutment pressure of the “square stage” exists three parts, that is the initial affect range, significantly affect range and severe affect range. The initial and normal mining stage has no obvious rising stage. The abutment pressure affect scope and the peak stress of the “square stage” are 1.5-1.7 times higher than those of the other two stages. According to the characteristics of abutment pressure distribution, reasonable advance support distance and controlling measures of different recovery stages were determined.

Risk evaluation of powered support jammed in working face with a raise of mining upper limit based on comprehensive index method

LI Zhihua, HUA Xinzhu, YANG Ke, GE Shengwen

2015, 32(3):  389-395. 

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It was difficult to accurately assess the risk of powered support jammed in upper exploitation limitation-heightened working face due to the complexity and abruptness of powered support jammed accidents. Through system analysis of the effect factors and risk indexes caused by the geological and mining technology conditions of powered support jammed danger, a classification forecast method of powered support jammed in raise working face has been proposed with comprehensive index method, and the comprehensive index of powered support jammed has been determined in this paper. The hazard degree of powered support jammed can be divided into four classifications: no risk, weak risk, medium risk and strong risk; the corresponding preventing measures have been proposed according to hazard degree and main effect factors. According to the application results of this method in some engineering practice, the evaluation results are basically consistent with the actual situation, which proves that the evaluation method can be used in powered support jammed prediction.

Development regularity of mining-induced fractures in mixed mining of coal seam group

HU Yongzhong, LIU Changqie, LIU Changyou, CHEN Baobao

2015, 32(3):  396-400. 

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In view of the important influence of fracture development regularity on roof control during coal seam group mining, based on the mining and geological conditions of Songhe coal mine in Guizhou province, the development regularities of rock fractures during mixed-mining of coal seam group were studied by using physical simulation test. Studies show that when using mixed-mining in coal seam group，the development degree of overlying rock fractures is influenced by composite thickness of coal seam, layer distance and mining sequence, etc. In descending mining, the mining of lower seam lead to the ratio of fractured zone height to mining height of the upper seam increasing. In ascending mining, the ratio of fractured zone height to mining height is relatively small after the upper coal seam mining，but the roof fractures in adjacent lower seam may be continuously developed, which making the ratio of fractured zone height to mining height increase. In addition, it show a logarithmic relation between the ratio of fractured zone height to mining height and coal seam composite thickness, while the relation between the fractures developing height and roof convergence shows three degree polynomial relation. The results can provide basis for roof control design in mixed-mining of coal seam group.

In-situ observation and numerical analysis of roof movement features of fully-mechanized sublevel caving face with deep alluvium

GUO Xinshan，LIU Jinhai，JIANG Fuxing

2015, 32(3):  401-406. 

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By using the in-situ observation and numerical simulation, the roof moving features of fully-mechanized sublevel caving face with deep alluvium has been studied. The results can be drawn as follows: 1) The time effect of the load of supports in the fully mechanized caving face with deep alluvium is significant. 2) While with advance of working face, the break of the immediate roof forms “rock-gangue” structure periodically and the break of the basic roof induces weighting of working face. 3) The weighting order along incline direction of the working face follows roof fracture characteristics of general working face. 4) The area of overlying strata area to be controlled by supports is large, and the strength of weighting induced by the upper basic roof breaking is large. 5) The advance stress fluctuation monitoring technology offers a new method for weighting prediction in working face. Finally, the suggestion about roof accident prevention of fully-mechanized sublevel caving face with deep alluvium was proposed. The study results can be useful for roof control design and roof accidents prevention in fully-mechanized sublevel caving face with deep alluvium.

Experimental study of deformation of wall rock and stoping sequence in mining gently inclined and multilayer deposits by backfill mining

YE Yicheng，SHI Yaobin，WANG Qihu，LIU Yanzhang，YAO Nan，LU Fang

2015, 32(3):  407-413. 

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Based on the characteristics of gently inclined and multilayer ore body, a similitude material model has been constructed through similar simulation experiment, to analyze its strain variation of stope and roadway surrounding rock, surface subsidence deformation characteristics in advancing and retreating filling stoping mining and discuss the reasonable mining sequence in mining Shanghengshan mine by subsequent filling method. The result shows that the deformation of surrounding rock has obvious characteristics of intermittency and discontinuousness in different strata, and strain near the rock and ore body contact area has greater gradient variation. The tensile strain area in advancing mining is 15.28% less than that of retreating mining. The strain state in tunnel roof and sidewall far from the ore tends to change from compressed to tensed one with the distance between stope and tunnel increasing. In addition, the ground settlement range is not symmetrical centered with the gob. The advancing mining method is one of the better mining sequences.

Research on splitting model based on curve propagation path involving closure effect

PU Hai，NIE Taoyi

2015, 32(3):  414-419. 

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Splitting failure zones always appear in deep surrounding rocks. In response to this phenomenon, the research has introduced REV and considered closure effect of pre-existing fracture. The hyperbolic curve has been applied to simulate the wing crack propagation path, and a splitting failure model has been established based on curve propagation path. From the microscopic point of view, stress intensity factor and maximum tensile strain theories have been applied to deduce the splitting crack propagation evolution equation. A new method to predict splitting failure has been obtained. FISH language has been applied to embed equation into FLAC, thus this new method has been programmed. The new model is well consistent with Lajtai empirical results. Compared with the old model, new model calculated results are more precise. The maximum decrease of relative error is 25.5% by using new model.

The experimental study of the grout quantity effect of strength properties of coal sample

KONG Dezhong，YANG Shengli，ZHANG Jinwang，XU Wenbin

2015, 32(3):  420-425. 

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The coal wall grouting reinforcement technique is an effective measure to prevent and control rib spalling, and its key procedure is the selection of grouting quantity. To overcome the difficulty in choosing the reasonable grouting quantity, an experimental scheme“The fragmentized and broken coal molded again with mixed slurry”has been designed. The uniaxial compressive and the wedge shear test of coal sample with different proportion of grout has been performed by using the rock mechanics testing machine. The study has shown that: the coal shows much less brittle failure because the grout in it can continue the deformation of the coal sample; the uniaxial compressive strength and residual strength of the coal sample can reach the maximum amount with an appropriate proportion of grout; the shear strength of coal sample is increased because of the grout in it, which is shown as the phenomena that the cohesion of coal sample is increased ,while the influence of friction is little. It has been concluded that the research result can provide the theoretical foundation for the selection of grouting quantity.

Stability and control technology of overlying structure in gob-side entry driving roadways of deep inclined coal seam

WANG Meng，BAI Jianbiao，WANG Xiangyu，CHEN Bin，HAN Zhiting

2015, 32(3):  426-432. 

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Based on theoretical analysis, mechanical model of overlying structure in gob-side entry driving roadways of deep inclined coal seam has been established; the relationship between stability of overlying strata key block and burial depth, dip angle of coal seam during recovery period has been analyzed, which has indicated that main motion form of the key block during recovery is rotational instability, and precondition of maintaining roadway stability is to control rotational instability of the key block; the effect analysis of roadway-inner supporting resistance on rotational instability coefficient of key block has indicated that the sensitivity of rotational instability coefficient of key block to carrying capacity of narrow coal pillar and roof is much more intense than that to solid coal pillar, so improving capacity of narrow coal pillar and roof can control rotational sinking of key block effectively. Based on high strength bolting system, gob-side entry driving asymmetric coupling control technology in deep inclined coal seam has been put forward with core technology of high-resistance yielding support of roof and inclined traversing seam anchor cable enhancing narrow coal pillar. Bolting parameter of testing roadway has been confirmed by system information designing method. And finally, it will be applied to engineering practice successfully.

Mechanical analysis of the plastic zones propagation of loose soft rock roadway and the supporting practice

ZHANG Jihua，WANG Lianguo，ZHU Shuangshuang，LI Qinghai

2015, 32(3):  433-438. 

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In response to the poor cementation condition of loose soft rock roadway and obvious features of layers of granular mechanical behavior, this paper has introduced granular material to study the instability mechanism of loose soft rock roadway. Based on the analysis of static mechanical behavior of granular materials，the research has obtained Coulomb Yield Criterion of granular material; combined with the present specific situations of a certain mine field, the roadway supporting mechanical model has been constructed and surrounding rock plastic zone extension formula under the poor cemented geological conditions has been obtained. By analyzing the results, this paper has shown that the roadway plastic zone radius decreases as the ratio of the strength of initial support and the primitive stress increases; but the plastic zone is still very large. So only by raising the strength of initial support of the roadway can we control the expansion of such roadway plastic zone effectively, and it also needs to improve the physical and mechanical rock properties and increase the carrying capacity of supporting structure. As a result, the “pre-grouting + anchor net shed + bolt-grouting” united supporting scheme has been proposed, which has achieved good efficiency and ensured the smooth construction process.

Multiple disturbance instability mechanism of dynamic pressure roadway and mining sequence optimization

LI Jiazhuo，ZHANG Jibing，HOU Junling，WANG Lei，YIN Zhiqiang，LI Chuanming

2015, 32(3):  439-445. 

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The instability mechanism of 1113(1) working face mining roadway under repetitious disturbances during excavating in multi-seam mining environment has been studied by means of integrated research methods of numerical simulation, field measurement and theoretical analysis. According to the data calculated through simulating different mining sequences of four working faces in coal seam group, diverse mechanical environments of surrounding rock mass of mining roadway have been reproduced. The results show that the mining of 1113(1) working face activates disturbed overlying interlayer appearing continuous rock mass, discontinuous rock mass, and bulk solid structure, exacerbates wide range of constant severe deformation of 1113(1) working face mining roadway in shallow high stress environment, and the outstanding characteristic is large amount of floor heave in present mining conditions. That is the mechanical nature of instability of 1113(1) working face roadway. Mining sequences have a significant effect on the stability of surrounding rock of mining roadway in coal seam group mining. The deformation and destruction are also smallest by adopting downward mining and underlying mining. If adopting neighbor coal seams riding mining at the same time, failure area of the surrounding rock and deformation of 1113(1) working face mining roadway will be most severe in the environment of floor aggregate high stress of 1113(3) working face, 1113(1) working face mining disturbance, and the excavation of 1113(1) working face roadway. Downward mining should be adopted as the first choice, and multiple mining effect should be avoided.

Determination of the narrow pillar width of gob-side entry driving

ZHANG Kexue, ZHANG Yongjie, MA Zhenqian, BI Wenguang, YANG Yingming, LI Yang

2015, 32(3):  446-452. 

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Gob-side entry driving in large pillar is a technology of roadway layout and maintenance. This paper, according to the specific geological conditions, based on the limit equilibrium theory, numerical calculation and the combination of industrial field tests, and through the stress field analysis, has concluded that if the coal width is of 3-5 m, the vertical stress distribution approximation shows obtuse angle triangle, the coal width of 5-8 m, the vertical stress distribution approximation shows acute angle triangle, the coal width of 8-10 m, the vertical stress distribution approximation shows trapezoidal. According to the analysis of the displacement field, pillar displacement of the roadway is generally greater than that of gob side, and as the pillar width increases to the roadway displacement, lateral displacement to the gob-side is relatively less affected. Finally certain method to determine the width of gob-side entry driving has been found, which needs workers to take five aspects into consideration including distribution of stress of the section of the lateral support goaf, stress field distribution, displacement field distribution, the relationship between deformation of surrounding rock and pillar width and limit equilibrium theory of narrow pillar width, and then that the narrow pillar width is five meter has been finalized. Industrial field tests have shown that the status quo of large deformation and severe damage of the roadway in the gob-side entry driving has been improved.

Study on the reasonable layout of gob-side remained gateway of lower coal seam close to coal seam group

CHENG Zhiheng，QI Qingxin，KONG Weiyi，ZHANG Lang，JI Wenbo，LIU Xiaogang

2015, 32(3):  453-458. 

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In response to the serious problem of deformation and fracture caused by repeated mining gob-side entry retaining in the lower coal seam, the reasonable location and the support parameter between the roadway and excavation have been studied by using numerical simulation filed practice and theoretical calculation. The result has shown that a certain range of stress-relaxed area below the goaf arises after the upper coal seam mining, which creates favorable conditions for gateway layout; However a certain range of stress-concentrated area below the residual pillar arises, and the influence outside scope of which spread to 10.8-11.54 m from coal pillar in coal seam 3+4. Adopting the method of multipoint displacement monitoring roof-floor and lanes convergence, the result has shown that the amount is within the controllable range. The arrangement and support design for the remained gateway along goaf, according to engineering practice, is reasonable. Research results have provided the basis and guidance for the reasonable layout and support design of gob-side remained gateway under similar conditions.

ANSYS-based bearing performance & stability analysis of U-shaped steel antiarch beam

ZHENG Xigui，LIU Na，FENG Xiaowei，ZHANG Nong，FU Shixiong，HUA Jinbo

2015, 32(3):  459-464. 

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In order to solve the instability problem of antiarch beam with U-shaped steel section, finite element model of which has been built with the co-assistance of CAD and ANSYS, the built-in non-linear buckling analytical module has simulated three kinds of sections including U25, U29, and U36 respectively, and all of them is under the impact of radical uniformly distributed load, thus relationship between buckling load, ultimate bearing force and central angle of antiarch is able to come into being, where the curve between vertical load and displacement of the uttermost point in the antiarch is monitored. The results have shown that, critical buckling load reaches its peak value as central angle is 70° as to all those three sections, then the load will glide down at the rate of 4.0% with the continuous increase of the angle, it thus manifests that 70° for central angle is optimum for overall stability. If the angle is less than 70°, the load will mount at the rate of 34.3%, however, if the angle is more than 70°, the mounting rate of the load will mitigate at the rate of 14.5%. The results have provided feasible methodology and theoretical foundation for engineering practice.

An analysis of “space-time” relationship of gob-side entry driving in dynamic pressure area

MA Depeng，WANG Tongxu，LIU Yang

2015, 32(3):  465-470. 

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In response to the problems of supporting, large deformation of surrounding rock in the process of gob-side entry driving in dynamic pressure area of fully-mechanized oil shale mining, comprehensive analysis of space-time relationship between driving and stoping, reinforcement scheme, and repairing techniques have been carried out. To start with, based on the theory and numerical simulation analysis, the deformation and stress distribution law of surrounding rock have been obtained, and then the driving method of roadway can be initially determined; after that, based on the observation results of mining pressure, the reasonable space-time relationship between driving and stoping has been set down. When driving is conducted, the reasonable delay distance is 136 m and the lagging days should not be less than 36 days; while when driving and mining are in opposite directions, the distance crossing the stopping line should be less than 50 m. According to the result of deformation observation, reinforcement scheme and repairing techniques are respectively designed for different locations of roadway, and the roadway can meet the production requirements after reinforcement or repair, which shows a certain guiding significance to the gob-side entry driving under the similar conditions.

Influence of weak interlayer contacts on the stability of shale gas wells transiting minable coal seams

LIANG Shun，LI Xuehua，YAO Qiangling，YANG Dong

2015, 32(3):  471-477. 

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Weak contact between layers with different properties is one key factor affecting the stability of engineering structures, e. g., slopes, underground roadways, and chambers. The movement of overlying strata induced by coal mining is the main reason for the damage of vertical shale gas wells drilled within the mining affected areas. By using two-dimensional geological model, predictions have been made about various well deformations, e.g., shear slippage, bed separation, tension and compression, and the effect of weak contacts between layered strata on the stability of gas wells piercing a coal seam has been analyzed. The axial heights at which the gas well is prone to failure has been acquired through the analysis of the axial distribution characteristics and various deformation of well holes in the different positions of coal pillars, according to which the position of the well has been optimized thereafter. Results indicate that the “interface” element in FLAC is excellent in realizing the possible deformation responses occurring at weak interfaces caused by coal mining, and it is very commendable in characterizing the shear failure mode, which is the major mode of well instability.

Principal stress difference evolution in floor under pillar and roadway layout

XU Lei，ZHANG Hailiang，GENG Dongkun，LI Bo

2015, 32(3):  478-484. 

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Floor principal stress difference distribution characteristics of 8# coal pillars was simulated by FLAC3D and theoretical analysis. Research results are as follows: ① The principal stress difference near coal pillar edge transfers to floor in 45 degrees; the farther distance to coal pillar is, the wider the diffusion range is, and it decays gradually. ② When the pillar is narrow, influence depth of midline and edge is shallow. When the coal pillar has increased with a central elastic core, floor varies obviously and influence depth is big, and if the coal pillar is wide enough, the middle part is as stress of primary rock. ③ Principal stress difference in midline and coal pillar edge decreases to depth in the form of negative exponent. ④ In the same horizontal plane, principal stress difference are distributed as saddle shape. ⑤ With pillar width increasing, principal stress difference in the coal pillar midline and edge increases at first and then decreases; however principal stress difference peak position in coal pillar edge outer margin decreases at first and then increases. It has proved that: ① Inboard-type layout could avoid principal stress difference peak, and roadway is in the low principal stress difference environment;② Enough inboard distance could avoid major principal stress difference change rate. With in boardtype layout of 20 m in 9207 belt roadway, the average principal stress difference is below 1.5 MPa. Both sides maximal relative convergence velocity is 6 mm/d; roof-to-floor maximal relative convergence velocity is 7 mm/d; Self-stabilization period is 10 days; both sides relative convergence is 87 mm and roof-to-floor relative convergence is 97 mm.

Research on surrounding rock deformation characteristics of gob-side entry driving in deep inclined coal seam and its control technology

CHEN Xinzhong，WANG Meng

2015, 32(3):  485-490. 

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The paper has analyzed the stress field and displacement field of surrounding rock of gob-side entry driving in deep inclined coal seam at driving stage and mining stage, and revealed the asymmetric large deformation characteristics of such roadway. The deformation amount of narrow coal pillar rib and floor was greater than that of solid coal mass rib and roof, and the convergence rate of whole roadway section is large. Reasons contributing to such deformation and failure characteristics have been pointed out as below：1) As the roadway is buried in great depth, the surrounding rock is located in high stress environment; 2) The width of roadway protection is not enough and the supporting resistance is too small, which make the surrounding rock enter the residual bearing stage too early; 3) Unsupported floor as the main releasing channel for deformation and failure energy, has intensified the whole subsidence of roof surrounding rock. The paper has reasonably determined the width of roadway protecting coal pillar and the supporting technology and parameters of testing roadway. Engineering practice has showed that after adopting new supporting technology, the asymmetric large deformation of narrow coal pillar and floor has been controlled effectively, which has maintained the long term stability of the testing roadway.

Research on the law of internal deformation and cracking of circular tunnels under non-tectonic stress

LIN Zhibin，LI Yuanhai，GAO Wenyi，ZHANG Shunjin，GUI Changlin

2015, 32(3):  491-497. 

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To obtain spatio-temporal evolution rule of deformation and fracture in the rock under high pressure stress, set in a deep roadway of Pingdingshan Coal Mining Group, physical and numerical simulation of excavation process has been performed by using transparent rock-similar materials and three-dimensional particle flow code software called PFC3D. The evolution rule of deformation and fracture in the rock changing with excavation process has been acquired. On this basis, supporting measures of deep circular roadway have been put forward. Research results are as follows: 1) The experimental method of transparent rock in this paper can effectively obtain the spatio-temporal evolution law of the internal deformation and cracking in deep rock mass. 2) Rock radial y-displacement at the roof and floor of model roadway decreases in an exponential relationship with the distance x from the roadway surface; after excavating, the deformation of surrounding rock grows fastest within one or two hours, and the deformation keeps basically stable two hours later without further excavation. 3) Rocks at the roof and floor of roadway don’t break after excavation, while shearing slippage fracture of rocks at the two sides appears in the hance and gradually expands into great depth in the direction of roof and floor with the passage of time.

Study on transverse railway effect of bolts in discontinuous rock mass

ZHOU Yu，SONG Hongwei，ZHAO Bin

2015, 32(3):  498-503. 

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By doing numerical analysis and physical tests, combined with orthogonal design, influence extent and law of various factors on transverse railway effect of bolt have been achieved. The result has shown that lithology is the biggest factor on axial stress of bolt, and effects of bolt diameter and friction coefficient increase with the shear shift. Diameter and anchorage angle are major factors on separation, and lithology is the most important factor when the shift is the biggest. Among the factors on strength of jointed rock, lithology comes first, and joint comes second. Other factors are positively correlated with shear force, except for anchorage angle. Based on the influence rules, internal mechanisms have been derived. Advanced laboratory test has shown that the results are in reasonable agreement with those acquired from experiment and the simulation model is suitable for modeling transverse effect. The research achievement has a positive significance on the jointed rock mass stability controlling by bolt and engineering security under the coal mining load.

Study on the influence of principal stress on the stability of surrounding rock in deep soft rock roadway

ZHAO Weisheng，HAN Lijun，ZHANG Yidong，ZHAO Zhouneng，WANG Guifeng

2015, 32(3):  504-510. 

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Taking some mine as the engineering background, the 105 groups of numerical simulation project have been designed according to the possible existence of ground stress type of deep soft rock roadway and to the angle alpha which represents the numerical value between roadway axis and the direction of maximum horizontal principal stress. The law of the stability of surrounding rock of deep soft rock tunnel excavation, changing along the coefficient of axial and radial lateral pressure coefficient (λy， λx) and the angle of the roadway axial (α), has been studied. Besides, both the weight of Nλn that stands for the factor of lateral pressure coefficient and Nα that represents the factor of axial angle in complex stress field have been studied. The results have shown that the suitable axial angle for the layout of roadway is related to the type of stress field, and that not only laying along the maximum horizontal principal stress is the most conducive to the stability of roadway surrounding rock; When the axis of roadway in deep rock does not parallel with the direction of horizontal principal stress, the horizontal principal stress (be it the maximum or the minimum) that is closer to the axis of roadway could be regarded as the axial stress, while the other horizontal principal stress could be taken as the radial stress.

Revival mechanism and disaster-causing process of old-large landslide on coal mine tunnel

LONG Jianhui，ZHANG Jining

2015, 32(3):  511-517. 

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Many coal mines in China are located in the toe of high and steep slopes or old landslide. Engineering activities lead to the geological disasters of slope failure or the old landslide resurrection occasionally. As far as large old landslides are concerned, normally it has a long cycle time for resurrected deformation, with slip direction varying from the conditions of stress field, and multistage destruction bring non-continuous, which also bring many problems in stability evaluation and scientific prevention of the slope. Zhujiadian mine landslide was taken as an example in this paper to figure out the engineering geological conditions in the landslide area, revival factors of landslide, deformation failure characteristics, and the temporal and spatial relationship between the engineering activities and landslide revivification through field survey and long-term monitoring. Furthermore, FLAC3D numerical simulation has been conducted for analyzing the slope stability and deformation under different stress conditions, such as caves construction, before and after the gangue filling and slope toe cutting. Under these circumstances, the change law of landslide of particle displacement, plasticity status and the shear strain increment and the characteristics of stress and displacement in the coal roadway located in the toe of landslide have been recreated. The result is consistent with monitoring results in the field.

Deformation and fracture and its supporting measures in soft rock roadway in Wangwa coal mine

ZHANG Jie，YANG Tao，WANG Bin，XIAO Qi，LIU Dong

2015, 32(3):  518-522. 

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In order to effectively control the deformation and failure of soft rock entry, rock structure and physical mechanics parameters and ingredient and field monitoring have been used in 1522-1 mining entry. Experiments indicate that the roof and floor belong to swelling soft rock and that the fractures in coal are well generated. Thus the reliability of the end bolt and bolt strength is depressed and difficult to form stability and effective load bearing structure. The support way can’t make rock-mass stress balanced, with the deformation of roof-floor and sides big and floor protrude serious. It can’t meet the requirement of deformation character of surrounding rock in the soft rock roadway. Based on experiments and field monitoring, the cause of deformation and failure of weakness rock mining roadway is obtained. The full length anchoring bolt and net support and reasonable parameter are put forward, which achieves good application effect.