Table of Content

15 July 2014, Volume 31 Issue 4

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Study on the influence of the characteristic of unconsolidated confined aquifer on its property of load transfer

WANG Xiaozhen, XU Jialin, ZHU Weibing, WANG Huan

2014, 31(4):  499-505. 

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In response to the issue of prevention of support crushing and water inrush disaster during mining under unconsolidated confined aquifer, a specialized simulation experiment set based on the mechanism of aquifer load transfer has been designed and the influence of occurrence characteristic of unconsolidated confined aquifer on its property of load transfer and key stratum compound breakage has been studied. The result indicates that load transfer effect on the unconsolidated confined aquifer is closely related to its framework grain characteristic. The larger the skeleton granule diameter is, the simpler the component is, and the better the property of flowing and replenishment is. Therefore it can transfer load to top overburden continuously and uniformly and make the load on top of overburden larger, which easily causes overburden integral breakage and results in support crushing and water inrush disaster. While the smaller the framework grain diameter is, the more complex the component is, and the poorer the property of flowing and replenishment is. Load applying on top of overburden can reduce during mining and aquifer load transfer coefficient can become smaller. Therefore, key stratum breaks layer by layer and hardly causes support crushing and water inrush. Calculating method of load transfer coefficient of unconsolidated confined aquifer has been confirmed. Load transfer coefficient should be 0.83 to 0.94 in alluvial and pluvial fan area of Qidong coal mine, while non-alluvial and pluvial fan area should be 0.69 to 0.71.

Stress and failure characteristics of surrounding rock in the extremely close distance coal seams group mining after the upper and lower coal seam mining

ZHANG Xiangyang, CHANG Jucai

2014, 31(4):  506-511. 

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In response to the engineering specifications of the middle coal seam mining after the upper and lower coal seam mining during the extremely close distance coal seam group mining, by adopting the numerical simulation, analog simulation and the engineering practice, the stress distribution, the displacement variation characteristics and the fracture of the stope surrounding rock during the extremely close distance coal seam mining has been analyzed. Results show that the roof and floor stress decreases, and its integrity isn’t badly damaged during the extremely close distance coal seam mining when the coal seam is not thick, the roof and floor rocks are relatively stable and the mining height are about 3 meters. While the surrounding rock stress concentration strengthens significantly at the range of the district sublevel entry outside. It forms a shear fracture zone 35 m near to the open-off cut and terminal line. During the extremely close distance coal seam mining, repair and reinforcement for the two roadways should be strengthened and the working face should be reasonably arranged to avoid the high stress zone and the shear fracture zone. Meanwhile the corresponding underground pressure control measures should be taken, ensuring the working face safety mining.

Roof structure characteristics in fully mechanized coalface with large mining height and reasonable loading of support

WANG Jilin, YUAN Yong, TU Shihao, LI Bo

2014, 31(4):  512-518. 

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In this paper, to determine the reasonable working resistance of support during fully mechanized mining with large mining height (FMMLMH), the roof structure characteristics of FMMLMH and reasonable support ability were studied by methods of theoretical analysis and in-situ measurement. The concept and discriminate method of key stratum in the immediate roof (KSIR) were put forward, according to the fact that the existence of hard strata with medium or thick thickness has vital influence on the collapse of overlying strata. Thus, the immediate roof can be classified into two types, typeⅠwithout KSIR and typeⅡwith KSIR, and the support working resistances of two types can be determined respectively as well. The results show that the main roof of TypeⅠwithout KSIR falls with a single-layer of voussoir-beam structure, and the support working resistance can be calculated by the weight of rock pillar with 6 to 8 times of mining height. Meanwhile, the main roof of TypeⅡwith KSIR falls with a double-layer of voussoir-beam and cantilever beam structure, which is formed with the break of KSIR and the main roof, and the support working resistance can be calculated with the thickness, hardness and layer horizon of the KSIR taken into account. With the increase of KSIR’s thickness or its hardness, or the lower horizon of KSIR, the support working resistance will increase. The research results have been successfully used in the determination of support working resistance in representative FMMLMH.

Rock burst characteristics and mechanism induced within an island pillar coalface with hard roof

LI Zhenlei, DOU Linming, WANG Guifeng, CAI Wu, HE Jiang, DING Yanlu

2014, 31(4):  519-524. 

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Using microseismic monitoring and rock burst records, the burst source, burst energy, damage area, damage scope and damage form etc. were located and analyzed statistically in this paper, and rock burst characteristics were summarized. Meanwhile, by means of theoretical modeling and calculation, rock burst mechanism in island pillar coalface was analyzed from the aspects of rock mass structure and stress state. The results show that all the burst sources are located at the adjacent gob and its edge due to the no breaking of the 60-meter-thick main roof and the secondary-movement of the adjacent gob overburden.With the coalface advancing, the maximum static stress within coal mass rises gradually and comes close to the critical stress. Thus, the superposition of such a high static stress and dynamic stress reaches the critical stress for rock burst, leading to frequent occurrence of rock burst. Both gateways near the designed ending line are the maximum static stress locating area. With a 0-1 m distance be-tween the gateway floor and No.15-3 coal seam, this area has been damaged repeatedly when rock burst occurred. Because of a higher static stress, the headgate has been damaged 6 times, 3 times more than that of the tailgate. The main damage form of the gateway is floor heaving since the floor is without support and the distance between the floor and coal seam is small. The analysis in this paper may provide a reference to rock burst control with similar conditions.

Relationship between microseismic events and abutment pressure distribution in coal mining

KONG Linghai

2014, 31(4):  525-531. 

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In this paper, based on the close spacing layout method of high-density geophones and near-field location principle of microseismic network, combined with mining theory, we analyzed the relationships between overburden strata movement and strata fracture, overburden strata movement and abutment pressure distribution, microseismic events and abutment pressure distribution, et al, and conducted the field survey study. The results show that mining disturbance can cause overburden strata movement and abutment pressure adjustment, which is the root cause of surrounding rock fracturing. Through analysis of strata fracturing and microseismic event distribution, it is concluded that the high stress distribution range ahead of workface is 75 m and the lateral high stress distribution range is 35 m. Ranges of fractured strata and high stress distribution of abutment pressure are all depend on the degree of mining disturbance on stope strata. Measured results of strata deformation show that the distribution difference between the extreme zone of microseismic events and obvious scope of strata pressure is about 19 m. The test results have proved the rationality of research conclusion by considering the layered strata characteristics and hysteresis properties of deformation after strata failure under high stress. The study can provide reference to the microseismic monitoring in coal mining.

Basic study on automatic detection of coal and gangue in the fully mechanized top coal caving mining

ZHANG Ningbo, LU Yan, LIU Changyou, YANG Peiju

2014, 31(4):  532-536. 

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The key to realize the automatic fully mechanized top coal caving mining technology is the automatic detection of coal and gangue. Therefore, detection of gangue rate in coal gangue mixture of drawing opening by using of the dual-energy γ-ray method has been proposed and the attenuation law has been analyzed when dual-energy γ-ray crosses the coal gangue mixture. Quantitative relationship is established between gangue rate and ash content. The parameters of the gangue rate and ash content by experimental analysis has been studied and their correlation has been built. Real-time response property of the equipment has been tested in the experiment. The results show that dual-energy γ-ray method is feasible for real-time detecting the gangue rate of coal gangue mixture.

Characteristics of extremely loose gravel roof and its support countermeasure

ZHAO Shujiang

2014, 31(4):  537-543. 

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To solve the supporting problem of rare extremely loose gravel immediate roof in Shajihai mining area, Xinjiang, the gravel layer characteristics, including particle size distribution, mineral composition, compressive strength, etc., were analyzed in this paper. Combined with the field engineering practice, a new composite support system with no legs was proposed, and the reasonable support parameters were determined through numerical simulation and theoretical analysis. Field simulation test has verified the reliability of this support system, which was applied successfully in the engineering field, and can provide effective practice experience for roadway support in similar geological conditions．

Active roof support technology of individual hydraulic props in Bainiuchang mine

KANG Baowei, WANG Yiming, WU Aixiang, XIA Hongchun, LI Qiang

2014, 31(4):  544-550. 

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It is a typical gently inclined, thin and troublesome ore-body in the deep level of Bainiuchang Mine. When using the overall mining method, it is difficult to manage the ground pressure and the operation safety can’t be ensured. Meanwhile, the loss of pillar left is huge when the room-pillar mining method is used. The roof supporting technology by using individual hydraulic props can be a good technology to solve the above problems. In this paper, the stope with its dimension of 40 m×8 m×4 m was studied by overall mining method and roof supporting technology of hydraulic props. Using slumping arch theory the support intensity and support density were calculated, which are 26.42 kPa and 0.275 root/m2, respectively. Meanwhile, the optimal proper space between hydraulic props is determined as 3 m×1.2 m by the calculation of FLAC3D. During the industrial test, by monitoring and analyzing the data such prop as setting load, sustaining resistance, descending amount of piston, and roof settlement, the roof supporting technology of hydraulic props can well control ground pressure of stope. Moreover, by regression analysis, the proper setting load and sustaining resistance of hydraulic props are 128.36 kN and 150.18 kN.

Multi-objective decision for mining method optimization based on weights assigned by fuzzy judgment matrix

TAN Yuye, SONG Weidong, LI Tieyi, XIA Hong

2014, 31(4):  551-557. 

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In this paper, selection of mining methods is handled as a system engineering problem with multi-objective decision-making．First, in consideration of technical feasibility, economic benefit, resource utilization, labor productivity, safety and environment factors, a comprehensive multi-objective decision-making index system for mining method optimization is built．Then, relatively objective fuzzy weights are assigned by fuzzy judgment matrix after consistency check and adjustment．Finally, an engineering project is conducted concerning filling mining method selection in Jinshandian iron mine．On the basis of primary classification by fuzzy clustering, the sublevel stoping filling method is selected as the optimal mining one by multi-objective fuzzy decision method．

Discussion on maximum mining height of coal mining under water-containing condition in one mine field of northern Shaanxi province

WANG Yue, XIA Yucheng, DU Rongjun

2014, 31(4):  558-563. 

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How to exploit coal resources under the premise of protecting the ecological diving, namely, the implementation of “coal mining under water-containing condition”, is a urgent technical problem to be solved in the construction of energy and chemical bases in Northern Shaanxi. Based on numerical simulation, taking a mine field in Northern Shaanxi as the research object, the growth regulation of water flowing fractured zone and the influence on ecological diving under different mining height were studied in this paper. The results show that the development height of water flowing fractured zone is mainly affected by the mining height. In order to realize the goal of “coal mining under water-containing condition”, slice and limit-height mining technology should be used in the study area. Based on this, the whole field is reasonably devided by limit mining height, which provides reference to ascertain the maximum mining height of slice mining．

Division of mining-induced fracture and permeability of overlying strata

XU Xingliang, ZHANG Nong, TIAN Suchuan

2014, 31(4):  564-568. 

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With the analysis of front abutment pressure distribution and mining-induced mechanical behavior of surrounding rock under the condition of relief failure, rock permeability changes in the front bearing stress environment are studied in the method of laboratory testing. Fracture development and evolution law of overlying strata under mining condition is revealed. The paper points out that the main cause of fracture development in front of the work face is strength failure, and the zone is divided into three parts: the original rock fissure zone, the stress concentration and fracture inoculation zone, the pressure relief and shear fracture development zone. The zone which has a better permeability accords with the plastic zone.

Fracture structure model of weakly cemented roof in shallow seam

NING Jianguo, LIU Xuesheng, TAN Yunliang, ZHANG Ming, ZHANG Lisheng

2014, 31(4):  569-574. 

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In this paper, based on the growth law of support circulation resistance in the fully-mechanized mining face of No.2-2 coal seam, Ordos basin, the fracture structure model of weakly cemented roof in shallow coal seam was built, the supporting strength formulas of hydraulic support in different roof movement stages were derived, and were compared with the field observations. The results show that there exits a rock beam composed of some squeezing rock blocks in the weakly cemented roof, which can be seen as a similar basic roof. The rock beam can not only transfer the horizontal force, but also reduce the impact of overlying strata on support. During the mining process of shallow seam, the moving process of weakly cemented roof can be divided into three stages. Stage one, the immediate roof caves, and the overlying sandy mudstone breaks, squeezes and generates separations. Stage two, similar basic roof breaks and forms the rock beam. Stage three, the basic roof subsides and impacts the support. With the working face advancing forwards, the growth of the support resistance can also be divided into three stages, which are initial increasing stage, slow increasing stage and significant increasing stage. This research can provide reference to roof control design, support selection, et al, in shallow seam of Ordos Basin.

Surrounding rock stability control with bolt support in seepage argillaceous roadway

WANG Cheng, HAN Yafeng, ZHANG Nianchao, QIAN Deyu

2014, 31(4):  575-579. 

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Because of the poor reliability of bolt support in seepage argillaceous roadway, roof fall accidents occur frequently. In this paper, typical rock disintegration and weathering experiments, field tests of roadway deformation rules and bolt anchorage performance in water seepage roadways were studied. The results indicate that once the clay mineral in roadway surrounding rock meet water, the rock will become sliming and weathering embrittlement, which will cause a sharply decrease in the load bearing capability. In addition, the deformation of seepage argillaceous roadway has obvious stage characteristics, which shows whole process of “decelerated deformation-weak argillization-accelerated deformation-strong argillization-instability”. Thus, the key point of stability control in such roadway is to control the argillaceous process effectively. Meanwhile, the surrounding rock control technology in seepage argillaceous roadway was proposed, which is composed of “there-high” bolt enhancement technology and lag grouting strengthening technology. Moreover, the best grouting time which is 10 to 30 days after the roadway drivage was given, engineering practice was then conducted, and good results were obtained.

Width of narrow coal pillar of roadway driving along goaf at large height mining face in deep mine

FENG Jicheng, MA Nianjie, ZHAO Zhiqiang, ZHANG Hao, YU Ziming

2014, 31(4):  580-586. 

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In order to solve the problem of low recovery of wide coal pillar at large height mining face in deep mine, the effect of plastic area distributions of the two sides of coal pillar and driving disturbance on the roadway deformation under conditions of different width of narrow coal pillar when mining at large height mining face in deep mine have been studied by theoretical calculation, numerical analysis and site engineering measurement. Thus the reasonable width of narrow coal pillar is determined. The results show that the stability of coal pillar and the deformation of roadway surrounding rock affected by driving should be taken into consideration to determine the reasonable width of coal pillar. The coal pillar is seriously crushed when its width of roadway driving along goaf is 5 to 6 m while driving, but it can achieve stability when its width is not less than 7 m. The width needs no less than 8 m while mining, and consequently the deformation of floor and coal pillar is less severe. So it is the optimal decision when the width of coal pillar is 8 m. field monitoring indicates that,the maximum deformation of the two sides of intake airflow roadway in 11030 workface is 1 210 mm, and that of roof and floor is 620 mm, which can meet the requirements of safety production.

Study on technology and mechanism of continuous“double shell ”harnessing floor heave in deep soft-engineering rock roadway

YANG Bensheng, GAO Bin, SUN Lihui, YANG Wanbin

2014, 31(4):  587-592. 

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Harnessing floor heave of roadway is one of the difficult but key problems in roadway supporting. The influence factors and mechanism of floor heave in the deep soft-engineering rock roadway are analyzed through site investigations and monitoring in the middle-strip track roadway at Xinjing Coal Mine. It is confirmed that the main causes of floor heave are that there is no support in the floor rock，which means the shear failure occurs firstly because of high-stress，and then stratum crushes further into squeezing and flowing because of water leading to further fragmentation. Therefore，the mechanism of the continuous “double shell” harnessing floor heave is studied by using continuous “double shell” to control floor heave and the technique of the continuous “double shell” harnessing floor heave that uses “bottom shallow hole grouting (shallow shell) +deep-anchor-beam with high-pressure grouting (deep shell)”to control floor heave is established. The technique has obtained a good effect.

Theoretical research and application on anchor cable space of synergetic support for U-shaped shed and anchor cable

ZHANG Hongxue, ZHANG Jihua, YAO Weifen, LU Xiaoyu, WANG Yunchen

2014, 31(4):  593-600. 

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In order to determine rational space between U-steel support and anchor cable in synergetic support system, the mechanical models of U-steel support and synergetic support for U-steel support and anchor cable have been established respectively. Anchor cable space in synergetic support has been determined by analyzing mechanical model based on principle of force method. It is studied that the anchor cable space in synergetic support for U-steel support and anchor cable relates to lateral pressure coefficient, the section size and burial depth of roadway. The analytical expression for lateral pressure coefficient of loose coal has been established. Furthermore, the synergetic support of U-steel support and anchor cable have been simulated. The result shows that deformation and plastic zone of surrounding rock in roadway and maximum bending moment of U-steel support are decreased notably due to reasonable spacing of anchor cable in synergetic support system of U-shaped shed and anchor cable, which achieves coupling support of U-shaped shed and surrounding rock as well as anchor cable and deep surrounding rock. The engineering practice shows that safety production in coal mine is guaranteed because of controlling the stability of surrounding rock of roadway effectively after reinforcing each key position of U-steel support by adopting anchor cable and joist steel.

Strength degradation model of fractured surrounding rock in deep roadway and its implementation in FLAC3D

NIU Shuangjian, JING Hongwen, YANG Dafang, WANG Jianwen

2014, 31(4):  601-606. 

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Based on the research result of strength degradation law of fractured surrounding rock at post-peak in deep roadway, plastic parameters having been selected as the damage factor, the value of plastic parameters (initial damage factor value) and the shear strength parameters c, φ in unloading point of rock samples with different damage degree are calculated respectively according to the results of the interior precast initial damaged rock samples loading-unloading test and triaxial compression test conducted under all levels of confining pressure. The strength degradation model of damaged surround- ing rock in the deep roadway is preliminarily established. Through the replacement and derivation of the plastic parameters in the preliminary established strength degradation model, the final strength degradation model of damaged surrounding rock in the deep roadway, represented by the plastic parameter εps, is established so that it can be directly applied to the theoretical analysis and numerical simulation. When the model is implanted in FLAC3D, and then combined with the actual deep roadway engineering, the numerical simulation analysis is conducted in deep typical deformed and failure roadway in km deep mine. After the comprehensive comparison of numerical simulation results and its related conclusions with interior physical simulation and engineering field test results, the reasonableness of the established model is verified.

Research on the evolutional course of surrounding rock structure along gob side with excavation of multiple working faces in close distance seam

SUN Xiaoming, WANG Dong, YU Shibo, WANG Cong, ZHENG Yalei, REN Xiaodong

2014, 31(4):  607-611. 

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By adopting the method of numerical simulation, a research has been conducted to study the dynamic evolutional course of surrounding rock structure of 93d05 working face along gob side after excavation of multiple working faces, in response to the complex geological condition of 93d05 working face with overlying and lateral excavation in Nantun coal mine. The corresponding dynamic evolutional course is obtained as follows: surrounding rock in the 93 d 07 working face along gob side within a range of 6 m is mainly cataclastic structure after excavation of 93 d 07 working face，and the rock in the other location around gob-side entry is mainly block structure；3 d coal roof is mainly cataclastic structure after excavation of 93u05 working face and 93u03 working face, and the other rock around gob-side entry is mainly block structure.

Random temperature field of shaft wall based on Monte-Carlo method

WANG Tao, ZHOU Guoqing

2014, 31(4):  612-619. 

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To study the effect of uncertain factors on the temperature field of shaft wall, by modeling the parameters such as heat transfer coefficient, heat intensity, specific heat capacity and medium density as spatially random fields, an analysis of calculating the temperature field of vertical shaft wall adopting Monte-Carlo stochastic finite element method has been proposed based on the local average theory of random field. The mean of temperature response of finite element node, computational formulas of mathematical expectation, variance and variable coefficient have been given. According to the calculation steps, the stochastic finite element calculation program for solving the temperature field of vertical shaft wall has been compiled by the MATLAB software. An engineering example has been presented in order to demonstrate the effects of random field parameters on the temperature field of vertical shaft wall. These results have been compared with the results derived when the random parameters was only dealt with random variable. The results show that Monte-Carlo stochastic finite element method based on random field theory can consider the uncertainty of thermal parameters for shaft wall reasonably. Stochastic finite element calculation program compiled by MATLAB software can directly output the statistical results of the temperature field for shaft wall. The traditional certainty analysis about the temperature field of shaft wall has some defects. It will overestimate the variability when thermal parameters of shaft wall is simulated as single random variables. Therefore, the method based on random field theory is more scientific and reasonable.

The prediction method for surface subsidence considering the geometrical characteristics of joints

YUAN Changfeng, YUAN Zijin, LIU Shibo, LI Guolong, LI Liang, YU Guangming

2014, 31(4):  620-623. 

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The similar material simulation test results show that the overlying joint rock mass subsidence caused by underground coal mining appears skewness characteristics. The geological and mathematical model considering the joint angle, trace length and the trace width is established and the probability distribution function of the overlying joint rock mass subsidence caused by the underground coal mining is deduced by using the random medium theory. At the same time, the probability distribution of surface subsidence caused by mass mining is assumed to be in accordance with the n-Bernoulli trial distribution. The n-Bernoulli trial distribution is equivalent to Poisson distribution when n is equal to or larger than ten. The overlying joint rock mass prediction equations considering the continuity of surface subsidence are proposed based on Gamma distribution (expanded version of Poisson distribution). The comparison between the results of surface subsidence computed by the model calculation and those measured by the similar material simulation experiment has shown that the presented model can predict a single set of joint rock mass subsidence caused by the underground coal mining with relatively good accuracy, which provides technical support for mining subsidence forecasting and strata movement monitoring.

Analysis of the deformation zone and its characteristics of the building foundations in mining-induced subsidence area

XU Ping, MAO Xianbiao, ZHANG Minxia, ZHOU Yuejin, CAO Zhengzheng

2014, 31(4):  624-630. 

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The deformation induced by mining residual cavities and fractures is a main reason causing damages to buildings in mining-induced subsidence area. In order to study the deformation characteristics of the building foundations in mining-induced subsidence area, by analyzing the distribution of the additional stress and the mining residual cavities and fractures in mining-induced subsidence area, the deformation zone of the foundations in mining-induced subsidence area has been studied. Based on the analysis of the detection for mining residual cavities and fractures and the distribution of the additional stress in the foundations, the deformation zone of the foundations in mining-induced subsidence area is above the soil depth, at which pz=0.1σz. However, when there are some mining residual cavities and fractures near this depth, the deformation zone in foundations should include mining residual cavities and fractures zone and its above area. According to the location of the buildings in Yima mining- induced subsidence area, the residual cavities and fractures zones under building foundations in mining- induced subsidence area have been detected by high density resistivity tomography method. In addition, the main reason causing damages to buildings has been demonstrated by analyzing the distribution of the stress and the deformation zone in foundations. The analysis of the distribution of the additional stress and the mining residual cavities and fractures zones also indicates that a proposed new structure will be affected by the deformation induced by the residual cavities and fractures zone, therefore, the new building foundation should be reinforced or changed.

Critical depth prediction and surface subsidence range controlling based on Xishimen mine

ZHENG Jianming, REN Fengyu, TANG Liexian

2014, 31(4):  631-634. 

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The traditional way of predicting subsidence range by stagger angle doesn’t adapt to production. This paper is to have a study of the relation between the height of critical bulk solid column in subsidence pit and subsidence range. After an analysis of lateral anchorage force of mobile bulk in pit, the paper proposed that the active pressure and passive pressure of dispersion both prevented the scaling of side wall rock while the thickness of bulk solid in pit is not less than the height of critical bulk solid column and the related factors affecting the height of critical bulk solid column is researched. The results show that filling subsidence pit with waste can lower the critical depth and control surface subsidence range.

On stress distribution of bolt in pullout test based on FBG

ZHANG Guihua, CHAI Jing, LI Yi, MI Xufeng

2014, 31(4):  635-638. 

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In order to detest the stress distribution of the anchor bolts, a fiber Bragg grating(FBG) optical fiber sensing technology was adopted to build a long-term bolting quality online monitoring system.. The rock bolting process and forces existing in a coal mine tunnel are simulated in the laboratory and the bolt pullout test has been conducted. By fiber Bragger grating the strains of the anchor bolt are measured. Then the strain dates are fitted with Gauss function. The axial stress distribution and the shear stress distribution are got. The experiment results show that it is feasible to test strain of the anchor bolt by FBG. The axial stress can be fitted accurately by Gauss function. The parameter t of the Gaussian function is related to the grip ability of the rock. The shift in changing direction of parameter t indicates that the interface between the rock and the bolt is changing and the grip ability of the rock begins declining. The research result can be a reference for the real-time monitoring of anchor bolt quality.

Research on confining pressure sensitivity and anisotropy for gas shale permeability

CHEN Tianyu, FENG Xiating, YANG Chengxiang, CAO Weidong, LIU Xiaoyu

2014, 31(4):  639-643. 

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MTS has been used to study the effects of confining pressure on permeability, deformation and the anisotropic characteristics of Niutitang gas shale. SEM has also been used to observe the samples' microstructure, which reveals the real reason of the confining pressure effect. The results show that: 1) The Niutitang gas shale permeability is between 5.06×10-7 D and 1.02×10-5D as the confining pressure raises from 0 to 40 MPa; 2) The gas shale permeability decreases with the increment of confining pressure, which obeys a power-law relationship, but the volume deformation of shale increases as confining pressure gradually increases; 3) The gas shale permeability and deformation are anisotropic, that is, under the same confining pressure, the permeability and volume deformation of sample paralleled to bedding plane are both greater than the sample with beddings at an angel of 45 degrees to the plane; 4) Obvious sedimentary structure is observed in the gas shale samples, and the pores distribute along the direction of the bedding; 5) The volume strain sensitivity to the confining pressure of low permeability gas shale decreases after an initial increase with the increase of confining pressure, and the permeability sensitivity to the confining pressure is gradually reduced with the increase of confining pressure.

Experimental study on the influence of longitudinal fissure on mechanics characteristic of sandstone

SU Haijian, JING Hongwen, ZHAO Honghui, WANG Yingchao

2014, 31(4):  644-649. 

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The roof mechanical characteristics in high horizontal stress roadway in the western mining area is simplified as a problem of rock sample containing the lengthways fissure under uniaxial compression. The strength, deformation and failure mode of sandstone which is chosen are discussed. The results show that, with the increasing of fissure length, peak strength and peak strain of sandstone containing a lengthways fissure first decreases and then rises slightly, and reaches the least value when the fissure length is 42 mm. Lengthways splitting failure in sandstone samples occurs along the prepared fissure tip, but the heterogeneity has an obvious influence on the number of main secondary crack and crack extending path. Comparing with the no-filling sandstone, gypsum filling is not apparent to the promotion of sandstone strength containing lengthways fissure; while the high strength cement has a good reinforcement effect with average peak strength increasing by 22.27%. The research achievement has a positive significance on the development of rock mechanics and the surrounding rock stability controlling theory in the western mining area.

Controlling effect of magmatic intrusion on coal and gas outburst

LEI Dongji, HE Shaopan, LI Hengle, GUO Xiaojie

2014, 31(4):  650-656. 

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In this paper, learning from the formation mechanism of magmatic rock in Qidong Coal Mine, we analyzed the distribution characteristics of magmatic rock intrusion, and the influence of magmatic rock intrusion to coal structure, the cause and distribution of tectonic coal, and abnormal gas occurrence, and illustrated the control function of rock intrusion to coal and gas outburst.The results show that the magmatic rock mainly intruded along the upper coal seam, which can change the lithology of partial coal seam roof and form a dense gas barrier layer, leading to significantly abnormal vertical zonation in coal and coal property, and the increase of the secondary hydrocarbon gas content, both of which control the abnormal gas occurrence. Tectonic movements were accompanied by magmatic activity, which has formed the concentration area of tectonic coal and local stress. The stress analysis shows the central air-return roadway is nearly SN direction.The angle between the maximum principal stress and roadway is large, and the coal stress of roadway in the drilling process is high, then the tectonic coal has formed. Meanwhile, the ability of tectonic coal to resist the external destruction is small, resulting in frequency occurrence of dynamic phenomena in the region.

Influence radius of slotted borehole drainage by high pressure water jet

GE Zhaolong, MEI Xudong, JIA Yajie, LU Yiyu, XIA Binwei

2014, 31(4):  657-664. 

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Drainage influence radius is the basic parameter for borehole layout, but the slot form of high pressure water jet slotting and its effect to borehole drainage influence radius have not been studied systematically. In this paper, slot shape was simplified as a disc according to the laboratory experiment results, and the disc size was analyzed based on the theory of submerged jet. Meanwhile, COMSOL software was used to study drainage influence radius of slotted borehole in different coal seam conditions, and filed tests were carried out. The results show that drainage influence radius of slotted borehole has power function relation with the slotted disc, as well as the permeability, time, and gas pressure, while the significant degree of the influence factors is in sequence of permeability, time, gas pressure and slotted disc. The relative difference of slot volume in actual high-pressure water jet slotting and slotted disc volume determined by theoretical analysis is about 8.33%. Meanwhile, when the drainage time is 130d, the relative difference of drainage influence radiuses between the measured and numerical simulation is 6.20%.