Table of Content

15 July 2015, Volume 32 Issue 4

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Fracture laws of one-side mined high-position hard thick key strata and microseismic energy distribution

JIANG Jinquan，ZHANG Peipeng，QIN Guangpeng，LI Fuchen，XU Bin，XU Lina

2015, 32(4):  523-529. 

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Aiming at the boundary conditions of one side mined working face, a plate model with three clamper edges and one simply supported edge was established as the mechanical model of high-position hard thick strata, and an energy releasing formula of hard thick strata fracturing was proposed. Deformation and rupture law of hard thick strata was revealed by comparing the maximum tension stresses in clamped edges of rock plate’s upper surface and the middle of lower surface. In addition, characteristics of microseismic energy distribution during the mining operation under high-position hard thick strata were analyzed combined with the microseismic monitoring data in field. Research results show that fracture happens at the same time in both lateral clamper side and the central of the lower surface when λ<1.024, the fracture form is an offset transverse “O-X” type, while the lateral span of the clamper side is lager than that of the simply support side. Otherwise, fracture first happens along the strike clamper edge, and the fracture form is a symmetrical vertical “O-X” type. During the mining process, small energy seismic events are mainly distributed in the rock mass below the thick key strata, and seismic events are easily triggered in the neighboring gob by the movement of lower rock mass. The high energy seismic events mainly happen in the fracturing process and losing stability of high-position thick key strata, mainly distribute near the fracture line of thick key strata, and concentrate in the vicinity of the internal and lower parts.

Real-time monitoring and early warning of rock burst risk in dip coal pillar area of extra-thick coal seam

WEI Quande，JIANG Fuxing，YAO Shunli，WEI Xiangzhi，SHU Couxian，HAO Qilin

2015, 32(4):  530-536. 

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By means of theoretical analysis and field observation, the occurrence cause of rock burst in dip coal pillar area of extra-thick coal seam, and the real-time monitoring and early warning technology were studied in this paper. The results show that the strata structure of dip pillar area and the asymmetric I-shaped spatial strata structure formed by excavation are primary causes of abnormal stress concentration. By establishing spatial strata structure model and strike abutment pressure calculation model in the dip pillar area, the stress distribution law of the overlying strata in the pillar area was obtained. It is revealed that the stress distribution area movement and value variation are the main causes of rock burst in the dip roadway near the coal pillar. In addition, the integrated monitoring and early warning of rock burst in dip coal pillar area were proposed, that is, the strata fracturing and movement were monitored by microseismic system, and the risk region of rock burst was predicted by index of microseismic momentum, while the risk level of rock burst was further predicted by borehole stress maters. Thus, the monitoring and pre-warning system of “regional monitoring and prediction and local monitoring and early warning” were established. The research achievements were applied to the dip coal pillar area of No.21 mining district, Qianqiu coal mine successfully.

Early strength concrete experiment and applied research of early strength concrete-filled steel tubular supports in extremely soft rock roadways

GAO Yanfa，LIU Keming，FENG Shaowei，ZHAO Wei，QU Guanglong，XIE Hao

2015, 32(4):  537-543. 

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When ordinary concrete-filled steel tubular supports (CFST supports) are used in extremely soft rock roadway, they are likely to be destroyed before the core concrete forms a larger strength. To solve this problem, the mixing experiment of early strength concrete has been carried out at first and then researchers have developed the early strength CFST supports based on previous experimental results. Further more, early supporting counter-force of early strength CFST supports and ordinary CFST supports have been contrastively analyzed by using theoretical calculation. At last, composite supports scheme based on early strength CFST supports has been designed and simulated with Beizao mine roof roadway as the engineering background, which has been used in engineering practice ultimately. Research results have indicated that the initial slump surpasses 220 mm, and the retarding time surpasses 3 h, and its 1 d compressive strength after final set surpasses 40 MPa, and that 3 d compressive strength surpasses 49.9 MPa,which have met pumping and early strength requirements; the 1 d，3 d and 7 d supporting counter-force of early strength CFST supports are 1.68 times,1.4 times and 1.26 times of the ordinary CFST supports, and it can still grow slowly in the late stage; numerical simulation and engineering application have sufficiently proved that the composite supports based on early strength CFST supports can effectively inhibit the convergence deformation of the extremely soft rock roadway in the early time and ensure the long-term stability of the roadway.

Study on asymmetric instability mechanism and control technology for roadway in deep inclined rock strata with weak plane

WANG Xiangyu，BAI Jianbiao，WANG Meng

2015, 32(4):  544-551. 

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By adopting methods of geological survey, theoretical analysis, numerical simulation and industrial test, the paper has analyzed the deformation characteristics of roadway in deep inclined rock strata with weak plane. Moreover, the paper has revealed the asymmetric instability mechanism of such roadway, mainly including shear failure mechanism in weak plane, expansion mechanism of high stress soft rock and the inducement mechanism of surrounding rock instability of weak plane. Surrounding rock damage initially appears along weak plane. The shear-slip deformation in weak plane layer causes expansion of the failure zone of adjacent surrounding rock. The partial surrounding rock instability intensifies the deformation failure of other parts, which induces catastrophic instability of whole roadway. As weak plane plays an induction role in roadway deformation, the key for maintaining roadway stability lies in controlling the shear deformation in weak plane layer and the continuous deformation inpost- peak bearing stage in soft rock zone after the instability of weak plane surrounding rock. Based on high-strength and high pre-stress control principle, asymmetric control principle and whole section control principle, the author has developed a staged dynamic control technology which needs strong support, reinforced support for weak plane surrounding rock, heave floor control and secondary support as technical core. Through reinforcing the whole strength and bearing capability of weak plane and surrounding rock, the technology could control the roadway asymmetric deformation and maintain the long-term stability of roadway.

A study on inward movement deformation mechanism and control technology of dynamic pressure gateway of island mining face

CHEN Xiaoxiang，WANG Leichao，FU Donghui

2015, 32(4):  552-558. 

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Based on engineering geological survey of Wuyang Coal Mine 7603 island mining face, researchers have done field investigation and analyzed the mechanism of large deformation in the process of “Inward movement”of two sides in the transportation tunneling, and have concluded that the roadway deformation mechanism is a compound deformation mechanism of Tectonic stress type and gravity deformation mechanism (IIAB)+Structural deformation mechanism of weak layer effects (IIIBA)+Bedding to the impact of structural deformation mechanisms (IIICA) + Random jointed structural deformation mechanism (IIIE). Using deformation mechanism transforming principle, this paper has proposed the supporting idea of “Relying on the top and bottom, controlling two sides”, and put forward a new support scheme. Using Numerical simulation FLAC3D this paper has also made a comparative analysis of the supporting effect of the new program with the original program, and has drawn the conclusion that the plastic zone development area of new program is 106.5 m² per unit less than that of original program. The roof-to-floor convergence of new plan is 65.4% less than the original plan, and the convergence of two sides has reduced by 78.9%. According to these findings, the study has shown that the new scheme can effectively control large deformation of the surrounding rock. The industrial test has shown that the largest roof-to-floor convergence of transportation roadway is about 250 mm, and the maximum amount of two sides convergence is only 350 mm, respectively, 45.9% and 79.2% less compared with the original support scheme; the force of two anchors between 110-160 kN, and the force of anchor wire about 300 kN, have all stabilized at around 15 d, and the roadway surrounding rock has been effectively controlled, so that it could ensure ventilation and safety to meet production needs.

Analytical calculation of the pressure in coal roadway sidewall and the bolt parameters

FAN Jincheng，JIANG Binsong，ZHANG Qiang

2015, 32(4):  559-564. 

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For high production and efficiency, roadways at mining area are generally arranged along coal seams with large rectangular section. Due to weaker strength of coal seam compared with the overlying strata, obvious mine pressure and large scale of rupture in sidewalls often appear, which have always been great threats to coal roadways stability and production safety. Currently, being an important reinforcement technique, the high-strength anchor (cable) supporting system has been widely used to maintain coal roadway stability, but supporting parameters, such as anchor length, diameter, and anchor arrangement are mainly determined empirically, not dependent on theoretical calculation. Considering rectangular coal roadways and overlain horizontally layered rock and based on the key strata theory in ground control and the elastic foundation beam model, this paper has firstly obtained the analytical expression of stress and the deformation of rock beam, to determine the pressure loading on sidewalls as well as the rupture range. On the basis of this, according to stability principle of geotechnical engineering, the anchoring force required for maintaining sidewall stability has been further studied, which can provide a theoretical basis for determining supporting parameters. Finally, through an example, the pressure loading on sidewalls and the bolting parameters have been calculated, and the result is in good agreement with the engineering practice.

Study on control technology of shallow arch floor beam support in preventing floor heave

LIU Jianzhuang，YANG Zhongdong，LIU Shudi，GUO Liwen

2015, 32(4):  565-570. 

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The existing available closed support has some defects in application because of its deep arch floor beam. Therefore，a new support with higher horizontal resistance, characterized by shallow arch floor beam has been designed in this research, and also its leg-shed-lapping method has been analyzed. By using ANSYS12.1, the mechanical characteristics of shallow arch floor beam and deep arch floor beam have been simulated and analyzed. The results have indicated that the former one has more capacity to bear horizontal extruding force under uniform load intensity of 1 kN/m, and the bending stress takes up less parts, and it has better spatial stability and is more sensitive to sagitta. Moreover, the shallow arch floor beam had another advantage in bearing horizontal concentrated load, which is important to prevent shear-slip floor heave. The shallow beam has been proved to be effective in controlling floor heave in Linnancang Coal Mine in Kailuan, which has verified the accuracy of the simulating results.

Deformation failure mechanism of high stress deep soft roadway and its control

ZHANG Guangchao，HE Fulian

2015, 32(4):  571-577. 

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In order to solve the problems of large deformation and support of high stress deep soft roadway, taking Xingdong ore-980 as an example, combined with field study, numerical calculation and field test, etc, the degree of the large deformation and deformation failure mechanism of surrounding rock have been analyzed. The causes of its failure have been summarized as follows: fracture development and strong sensitivity, high crustal stress, complex geological conditions and hydro-physical property, according to which, the research has indicated that ore-980 roadway is the stress dilatancy expansion type composite geological soft rock. The main reasons for the instability of ore-980 roadway have been found to be the development of surrounding rock fracture and the lower strength (under the high stress disturbance) leading to a wide range of breakage, together with the hydro-physical property, complex geological structures and rheological characteristics, resulting in the large deformation. Based on the above research，the multiple dimensions coupling support which is centered with high strength anchor, yieldable ring support and grouting reinforcement has been proposed, and surrounding rock coupling support mechanism and specific support form have been analyzed, and the design of parameters of concrete support has been done. Field practice has shown that after 60 d of expansion of ore-980 roadway, the convergence rate of surrounding drops 1 mm/d with roof subsidence reaching 193 mm, roadway’s side deformation reaching 114 mm, floor heave reaching 151 mm，which has achieved the goal of effective control of deep roadway with soft surrounding rock.

Development and preliminary application for test rig of the vertical interaction between deep soil and shaft lining

ZHANG Chi，YANG Weihao，WANG Yansen，ZHANG Tao

2015, 32(4):  578-584. 

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In this article, a test rig applying to research on the vertical interaction between deep soil and shaft lining has been developed successfully. Vertical interaction test between saturated sand and C60 concrete shaft lining has been studied preliminarily. The test rig has three main technical parameters: the maximum effective test space is 820 mm×820 mm, the maximum pressure capacity is 24 MPa and the maximum depth of research soil is 1 200 m. The vertical shear test between saturated sand and C60 concrete interface shows that when the average interface normal stress is 0.2-0.4 MPa, the shear stress-shear displacement curve can be described by elastic-plastic model. The maximum shear displacement is about 0.53-1.11 mm. The ultimate static friction coefficient is 0.70-0.53 and the interface shear strength is 140-210 kPa.

Study on deformation and cracking laws around deep soft roadway based on the transparent rock

LIN Zhibin，LI Yuanhai，GAO Wenyi，ZHANG Shunjin，YANG Fang

2015, 32(4):  585-591. 

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In the physical model test of deep rock, the measurement on the internal deformation and rupture is a challenge. In order to solve the problem, based on the transparent rock simulation experiment, the digital speckle correlation deformation measurement method has been adopted and the spot methods have been further studied. On the basis, spatio-temporal evolution law of the internal deformation and rupture in deep circular tunnels without tectonic stress has been obtained. The conclusions are as follows: 1) the artificial filling spot method of transparent rock presented in this article could guarantee the implementation and accuracy of digital photographic deformation measurement; 2) under different buried depths, the radial rock displacement at the roof, bottom and two sides is in an exponential attenuation relationship with the distance from the roadway surface; 3) the number and overall length of macroscopic crack as well as the width of failure zone are in an exponential growth relationship with the depth, and the rupture fractal dimension satisfies linear growth condition with the depth; 4) under the tectonic stress, the shallow rock in the two diagonals should be key supporting parts around deep circular roadway. In addition to spraying anchor supporting of roadway, grouting reinforcement is necessary to the shallow rock in two sides and diagonal. The supporting structure around the tunnel should be linked into a unified whole unit by truss and grilling, forming an effective bearing ring to prevent sliding instability failure of roadway.

A study on damage proneness of coal pillars of different sizes under complicated compression conditions

HE Yaoyu，SONG Xuanmin，ZHAO Jinchang

2015, 32(4):  592-596. 

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Depending on actual compression conditions of on-site coal pillars, based on the characteristics of compression shear and tensility of rock mass damages, risk indexes of compression shear failures and tensile failures of coal pillars have been established through theoretical analysis, and the study has also analyzed the distribution laws of risk indexes of complicated compressed coal pillars and damage proneness characteristics of coal pillars, by adopting the method of numerical simulation, under conditions of different width-height ratios. The study has found that with the increase of coal pillar width, the compression-shear damage proneness, in turn, presents the characteristics of an elliptic structured type, an “X” + half elliptical, a half elliptical + double funnel type, and a half elliptical + double trapezoid structured type; tensile fracture proneness presents the characteristics of a rectangle hyperbola structure, an “X” + half elliptical, a double funnel type, and a double trapezoidal like structure. The ratio of height and width of coal pillars on risk indexes is of the periodic feature, showing itself as three stages of dramatic, gentle and zero impacts. The distribution of maximum principal stress represents an obvious end impact, when coal pillars compressed, complying with the Saint-Venant’s Principle.

Stress distribution of bolt based on rheological conditions

KANG Jichun，BU Qingwei

2015, 32(4):  597-602. 

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In order to explore the stress distribution of bolt based on rheological conditions, at first, the visco-elastic plastic displacement solution of circular roadway under the condition of visco-elastoplastic model has been obtained, and then the expressions of bolt shear and axial stress of full-length anchoring bolt have been deduced by using “neutral point” theory. According to the site surrounding rock displacement data, four parameters value in visco-elastoplastic model has been derived reversely. The results show that the position of neutral point has nothing to do with time. When the rock is in the decelerating creep stage, the rate of increasing stress of bolt decreases and reduces to zero gradually. When the rock is in the steady creep stage, the rate of increasing stress of bolt decreases and reduces to a fixed value with the passage of time. This paper has provided a new way to verify whether the bolt is failure or not in roadway service life and to confirm secondary support time.

Overlying strata structure classification in working face of improving upper limit in Huainan mining area and theoretical calculation of critical support resistance of support crushing

LI Yingfu，LI Zhihua，HUA Xinzhu，YANG Ke

2015, 32(4):  603-609. 

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To avoid support crushing and water inrush disaster in the working face of improving upper limit in Huainan mining area, based on the comprehensive strength of strata in caving zone and whether or not existing hard stratum in fractured zone, the structure of overlying strata were divided into four types, namely, I, II, III and IV. In addition, the mechanics models of different strata structures were established, the critical support resistance was deduced, the instability criterion of support crushing was determined in the working face of improving upper limit, and the factors influencing critical support resistance of support crushing were further analyzed. The results show that the measures such as reducing length of working face, lowering mining height, keeping the integrity of immediate roof, preventing roof in the gob form suspending, strengthening the rib of working face, and drainage for decreasing water pressure before mining, etc. would be in favor of the stability of support in the working face of improving upper limit.

Mining disturbance of horizontal section full-mechanized caving face in steeply inclined coal seam

CUI Feng，LAI Xingping，CAO Jiantao，SHAN Pengfei

2015, 32(4):  610-616. 

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In view of the persistent mining disturbance from horizontal section top-coal caving, numerical simulation was used to study the distribution characteristics of plastic district, stress field and displacement field at the stages of mining current and next sublevels, and the surrounding rock stress distributions at next sublevel entries were intensively discussed. Meanwhile, the effect characteristics of mining disturbance were monitored and analyzed in field test. The results show that the disturbance effect of upper sublevel to next sublevel is weakened gradually with the increase of horizontal section height, and the larger thickness coal mass can play a cushion influence. In the next sublevel, the floor side stress in B3 roadway at +518 m level is larger, while the roof side stress in B6 roadway at +518 m level is larger. The advanced distance of mining disturbance affected by the upper sublevel is 10~20 m. Influenced by both the mining disturbance and caving effect of gob strata, the bolt tension variation in the entries of next sublevel is lagging behind the working face.

Fracture development of overlying strata by backfill mining under thick alluvium and thin bedrock

XU Ping，ZHOU Yuejin，ZHANG Minxia，LI Jiawei，CAO Zhengzheng

2015, 32(4):  617-622. 

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To analyze fracture development laws of overlying strata by solid backfill mining, by considering the thin bedrock under thick alluvium as a bearing structure above the solid filling materials, the model of Winkler elastic foundation continuous beam for the single thin bedrock was built, and the relation between the compression modulus of filling body and the fracture development height of single thin bedrock was obtained by the mechanical analysis. In addition, the correspondence between the fracture development height of single thin bedrock and the filling percentage were established by analyzing the compression characteristics of solid filling material. Combined with practical work, the UDEC numerical model based on mechanical analysis was further built, and the fracture developments of rock beam were analyzed with the filling percentages of 60%, 70% and 85% in solid backfill mining. The results show that the strata fracture development height can be inhibited by solid backfill mining duo to the supporting effect of filling body to the overlying strata during coal exploitation. Meanwhile, the strata fracture development height increases rapidly after the coal face moving forwards about 30 m to 50 m, and decreases rapidly with the increase of filling percentage. Thus, the solid dense backfilling is a safe and effective method in coal mining under the thick alluvium and thin bedrock.

Simulation of cover rock caving zone and fractured distribution in fully mechanized caving mining by strength increase finite element method (FEM)

LEI Wenjie，FENG Yongjun，WANG Zhaofeng，HAN Zhenli，YU Minggao

2015, 32(4):  623-627. 

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Based on the improving the derivation process on the yielding criterion of Drucker-Prager incircle under the condition of plain strain, the direct coefficient of transforming from Drucker-Prager incircle to circum-circle and the suitable application scope of strength increase on the internal friction angle have been deduced. Then based on the strength increase FEM, the limit analysis method of discrete medium has been put forward. The FEM model of the fully mechanized caving mine formed by coal seam and overlying strata has been built up. By the over-stratum and coal strength increasing, the model reaches its critical state in the roof and overlying strata under the periodic weighting. And the roof caving surface shape and the fissure distribution have been obtained automatically. The result of caving and fissure height by strength increase FEM has been confirmed by empirical method, resulting from which, a new method to analyze the features of discrete media of critical state has been provided.

An analysis of extra-thick coal mining influence on ground surface deformation under the condition of massive conglomerate stratum in Changcun colliery

LI Chunyi，CUI Ximin，HU Qingfeng，HE Rong

2015, 32(4):  628-633. 

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In order to research ground surface deformation law of extra-thick coal mining under the condition of massive conglomerate stratum, according to probability integral model, 3D distributed mathematical functions to determine optimum parameters have been made based on superposition principle. In response to ground surface movement surveying datum of 2113 panel of Changcun colliery, surface deformation prediction parameters have been obtained by using subsidence and horizontal movement functions. Associated with engineering geological data, parameters distribution law has been analyzed from overburden terrane movement mechanism. The results show that first weighing interval of thick conglomerate is 367 m, while period weighing interval of cantilever is 179 m. Ground surface discrete deformation present intensively after key-strata collapses. And the cantilever bear action of massive conglomerate stratum mainly causes dissymmetry subsidence basin. The results are in accordance with field surveying datum.

Relation between height of water flowing fractured zone and mining parameters

ZHAO Bingchao，LIU Zhangrong，TONG Chao，WANG Chunlong

2015, 32(4):  634-638. 

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To study the relation between the maximum height of water flowing fractured zone and mining parameters, combining with the generalized damage-factor definition of interlayer stratum and water flowing fractured zone, and assuming that two elliptical arcs could be used to fit the subsidence curve of rock-soil layer above the water flowing fractured zone, the relation among mining height, bedrock thickness, loading layer thickness and generalized damage factors of water flowing fractured zone were deduced, which simplified the calculation method of determining the maximum height of water flowing fractured zone. The results show that there is a great relationship between the maximum height of water flowing fractured zone and mining parameters, and the mining parameters must be considered when determining the height of water flowing fractured zone. Meanwhile, the applicability and reliability of the calculation method has been proved by engineering instances, which provides theoretical foundation for the further study on water conservation mining.

Study on detection method of anomaly watery area for the floor rock stratum of the working face with high dip angle

ZHANG Pingsong，FAN Jin，WU Rongxin，GUO Liquan

2015, 32(4):  639-643. 

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In the old mining area of Huainan coalmine a mass of the working faces with high dip angle often poses a threat of water disaster from limestone stratum of the working face floor during the exploitation process of coal seam group A. The detection and disposing measure must be done ahead of mining schedule. But the method applicability of penetration by direct electrical method for the coal seam with high dip angle needs to be confirmed. In the article the physical model has been conducted according to the mining geological conditions of coal seam group A with high dip angle, and test experiment has been finished. Through exploration practice, the imaging method of parallel penetrating with direct electrical method between double laneway of working face is studied, and the cognition for the key technology of data collecting, process and inversion about 3D penetrating of electrical method have been gained. Through the data collection and process of 3D whole space, the penetrating method with direct electrical method can get good resolution effect for the containing water characteristic of the floor rock stratum. It can provide the basis for formulating the technical measures of water control for the working face with high dip angle.

The analysis of antireflection range in coal seam hydraulic fracturing

ZHAO Yuan，CAO Shugang，LI Yong，QIN Le

2015, 32(4):  644-650. 

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Based on the theoretical analysis of crack initiation mechanism and crack direction of hydraulic fracturing, the hydraulic fracturing process of coal seam under five different in-situ stress situations has been simulated by using the seepage-stress coupling analysis system of coal and/or rock damage & fracture process, and hence, the crack initiation direction, initial pressure and expansion pressure have been obtained. Studies have found that, the crack direction is vertical, with the initial pressure as well as the expansion pressure presenting as gradual increasing trend when the lateral pressure coefficient λ<1. When the lateral pressure coefficient λ>1, the crack direction is horizontal, with the initial pressure and the expansion pressure presenting as gradually decreasing trend. When the lateral pressure coefficient λ=1, by carrying out three different kinds of yield criterion contrastive analysis, the minimum initial pressure are respectively obtained under the different kinds of yield criterion. Through the further stress analysis, i.e., when coefficient λ=1.2, studies have proposed that the antireflection range of hydraulic fracturing is the summation of macro-crack zone, micro-crack crossing zone, micro-crack generation zone (tension zone) and native crack disturbed zone (pressure recovery zone); the growth trend of anti-reflection area which has been obtained by digital image processing accords with quadratic function.

Experimental examination of permeability of deep rock mass under high water pressure

HUANG Zhen，JIANG Zhenquan，SUN Xiaoqian，CAO Dingtao，WANG Zongsheng，XIN Bin

2015, 32(4):  651-657. 

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Water injection experiment is a particularly useful technique to determine the permeability of rock mass in deep geotechnical engineering. To probe the permeability of lower coal seam floor, high borehole pressure water injection experiment has been carried out to analyse the three segments of rock masses in one coal mine in Yanzhou, and numerous data have been obtained. Based on the formula of permeability coefficient as well as the analysis of the data, permeability coefficients of three segments of rock masses have been determined, and a generalized model has been established to describe the relationship between permeability coefficients and pressure. The results show that the test pressure and the water discharge will suddenly change when the hydraulic fracturing occurs. The curves of permeability coefficient and pressure are provided with a significant geometric segmentation, which is stable before mutation and linear after mutation. Fissures will restore to be closed after water injection experiment, and the rock masses still have strong anti-permeability.

Stopes stability in underground mine and its control technique

XU Wenbin，SONG Weidong，CAO Shuai，JIANG Guojian，WU Feng，JIANG Lei

2015, 32(4):  658-664. 

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To study the stability of stopes in an underground mine, an approach to analyze the stability of irregular ore pillar was established on the basis of Voronoi diagram. Taking Dayin’gezhuang Gold Mine as engineering background, the collapse modes of ore pillars and roofs were investigated and analyzed, and the main factors influencing pillar stability was put forward. In addition, orthogonal polar difference analysis was used to investigate the sensitivity of influencing factors, and the affecting sequence was listed from the most to minor. The stability status of ore pillars at -496m level were evaluated, and the results show that the safety coefficients of No.1-2, No.2-6, No.3-1, No.3-2 and No.4-2 ore pillars are all below 1.0. The stability of No.6203 Stope is the worst, and the pillars are extremely vulnerable to failure contiguously. Finally, support control measures were taken to ensure the stope stability. It is proved that the occurrence of roof caving and ore pillar fracturing is rapidly decreased, and the whole safety of mining stop is significantly improved.

Acoustic emission and fractal characteristics of saturated coal samples in the failure process

GAO Baobin，LI Huigui，LI Huamin，LI Lin，SU Chengdong

2015, 32(4):  665-670. 

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To study the acoustic emission (AE) and fractal characteristics of saturated coal samples, focusing on coal samples of No.3 coal seam in Yuwu coal mine, an experimental study was carried out to investigate the acoustic emission characteristics of the dry, natural and saturated coal samples under uniaxial compression, by using RMT-150C rock mechanics test system and AE-win E1.86 acoustic emission instrument, and the fractal characteristics of acoustic emission count sequence was further analyzed. The results show that the uniaxial compressive strength decreases when the water content of coal samples increases. The acoustic emission evolution processes of dry, natural and saturated coal samples are similar, which can be divided into three stages, that is, the initial quiet period, the active period, and the post peak quiet period. Compared with the dry coal samples, the acoustic emission count of natural coal samples reduces 49.95%, and the cumulative acoustic emission count reduces 37.04%,while the acoustic emission count of saturated coal samples reduces 77.48%, and the cumulative acoustic emission count reduces 52.17%. All of the dry, natural and saturated coal samples have the fractal characteristics, and the fractal dimension value of acoustic emission presents the phenomenon of rising, drop and maximal value, which can be used as the precursor information of dynamic disaster prediction.

Influence of inner dump on end-slope stability

ZHOU Wei，HAN Liu，CAI Qingxiang

2015, 32(4):  671-676. 

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In order to study the influence of inner dump parameters change on the imbalance ground stress and end-slope stability, based on the development rules of the inner dump steps and the key theory of steep mining, FLAC has been used to simulate the northern end-slope in Haerwusu Open-Pit Coal Mine, and the imbalanced ground stress produced in the process of steep mining and the convergence effect produced by inner dumping have been recorded, then the synergistic effect of the inner dumping on end-slope stability has been analyzed. The results of research show that the inner dump steps can offset the imbalance ground stress well, showing good linear variation law. When the parameters of inner dump changes according to one dimensional, the relationship between the slope stability coefficient and the width will accord with quadratic function, and the height accord with linear function. When the parameters change according to three-dimension, the slope stability coefficient performance will be in a good exponential relationship with them.

Uplift mechanism of the bottom of open pit after the transition from open-pit mining to underground mining in Longshou mine

DENG Qinghai，CAO Jiayuan，ZHANG Liping，MA Fengshan，XU Jiamo

2015, 32(4):  677-682. 

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Based on GPS monitoring data, the movement and deformation rules of surrounding rock of open pit in the Longshou Mine of Jinchuan Company have been analyzed. The monitoring results show that underground mining has caused rock mass movement and large-range deformation, with two subsiding troughs separated by a central uplifting zone formed on the surface. The maximum settlement of the hanging wall sink area and footwall sink area are 767 mm and 1 078 mm respectively as well as the maximum uplift amount of the rising area in the open pit bottom are 648 mm. And physical simulation experiment has been conducted to simulate the movement and deformation process of surrounding rock mass of open pit from open-pit mining to underground mining. The experimental results are consistent with the monitoring results．And the uplift phenomenon of the bottom of open pit in both open-pit mining and underground mining stages has been clearly observed．Moreover, the uplifting mechanism of the open pit bottom after the transformation from open-pit mining to underground mining has been theoretically analyzed, from which a conclusion has been drawn that the earlier movement and deformation of slope rock mass caused by open-pit mining would be activated again by the underground mining activities. And when the uplifting amount of the open pit bottom caused by the activation is larger than its settlement caused by underground mining, the open pit bottom will rise because of the extrusion.

Three-dimensional limit equilibrium method for slopes under horizontal geo-stress

TAN Wenhui，SUN Zhonghua，LI Congcong，LI Ning

2015, 32(4):  683-688. 

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With the increase of excavation depth in open-pit mines, in-situ stress becomes an important factor affecting slope stability. Based on improved Spencer method, the formulas and program of three-dimensional LEM under horizontal geo-stress have been established and used in the slope of Shuichang open-pit mine. The numerical simulation results, using FLAC3D based on strength reduction method and the in-situ monitoring data of the slope, have been used to compare with the results of LEM. Studies show that the factors of safety under horizontal geo-stress by LEM and numerical simulation method are smaller than that without geo-stress, but the slip masses are bigger. Displacements under horizontal geo-stress gotten by numerical simulation are closer to the values from field monitoring. Therefore, the impact of geo-stress must be considered for stability analysis on deep-concave slopes.

study of physico-mechanical characteristics of slope hard rocks of metal mine influenced by freeze-thaw cycles

WEN Lei，LI Xibing，SU Wei

2015, 32(4):  689-696. 

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The experiment of cycle of freezing and thawing has been conducted using the rock specimens from Tibet Yulong copper mine slope containing granite porphyry，quartzose sandstone and limestone. Experimental temperature has been controlled between -20 ℃ and 20 ℃ according to meteorological data and natural environment of the mine, volume, quality, uniaxial compressive strength, tensile strength, coefficient of freezing and thawing, and the change rule of decay rate of hard rocks have been measured and studied under the condition of water saturated state. The relation curve of freezing-thawing cycles and uniaxial compressive strength, tensile strength, coefficient of freezing and thawing have been fitted using Matlab software. The experimental results have been applied in the slope of the Tibet Yulong copper mine. Safety factors of the slope before and after freezing-thawing test have been calculated and compared by using strength reduction technique. This study can be used for similar mines.