Table of Content

15 September 2015, Volume 32 Issue 5

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Study on the influence of temperature on the strength of wet shotcreting in cold mining areas & its application

Wu-Ai-Xiang, SUN Wei, HAN Bin, WANG Hong-Jiang, WANG Shao-Yong, LI Gong-Cheng

2015, 32(5):  697-705. 

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The wet shotcreting technology has been gradually applied to roadway support of fractured rock mass in extremely cold mining areas, and the temperature is critical to the strength development of wet shotcreting. This paper has introduced the low strength of spray layer, likely cracking and other problems occurred to wet shotcreting support in cold regions of Jinying Gold Mine, studied the rules of influence of temperature, cement content and water-cement ratio on the strength of spray layer, and adopted SEM to observe the microstructure of wet shotcreting. The results show that the initial strength of wet shotcreting reduces significantly when the temperature is below 10 °C, and the temperature above 16 °C is quite beneficial to the long-term strength increase; there is a critical range of cement content, and when the cement content is greater than the threshold, the strength of wet shotcreting increases significantly; the different water-cement ratios have a complementary effect on the strength development of different ages, because the low water-cement ratio helps increase the initial strength, while the high ratio helps increase the long-term strength; the temperature plays an essential role in the microstructure of wet shotcreting, and inner initial porosity and aggregate interface bonding strength cracking directly affects the macro-mechanical properties of wet shotcreting; when the temperature is lower than 10 °C, the aggregate interface intends to have microcracks due to different coefficients of thermal expansion; the daily spray amount has reached 40 m3 and the repair rate of wet shotcreting support reduced by 80% in Jinying Gold Mine by improving mixture ratio and technology.

Study on comprehensive control technology of roadway surroundings with large-dip angle compound strata in coal mine with depth of 1300 m

FAN Mingjian，KANG Hongpu，LIN Jian，REN Yongjie，ZHAO Peng，ZHANG Hui，ZHAO Guanglei

2015, 32(5):  706-713. 

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According to the geological and production situation such as compound strata with large dip angle, high level in-situ stress, roadway crossing through different strata frequently and so on, the suitable supporting forms and scientific surroundings control methods of roadway in deep coal mine have been researched. The paper has taken typical roadway with depth of 1 300 m in deep coal mine as engineering background. Some main supporting design ideas of roadway in deep coal mine have been determined by systematic geo-mechanical on-site tests, analyzing the characteristics of surroundings deformation and its failure zones. The comprehensive control technology with combining bolts-net-cables and grouting reinforcement could prevent large and endless integral deformation of roadway surroundings. It is also important to take some extraordinary supporting manners in specific regions to avoid roadway’s local failures. At the same time, some supporting components and materials such as W-shape plate with 4 ribs, full anchored and pre-stress grouting cables, high-efficient antifriction gasket for bolts were designed to meet the needs of surroundings control. The engineering practice has proved that the comprehensive control technology that combines full-face strong anchor net supporting with grouting reinforcement could make roadway surroundings in stable state, reduce roadway repair tasks and achieve effectively supporting by once for roadway surroundings in deep coal mine by solving the supporting problems of surrounding rock deformation, long duration and serious destroy.

Structural optimization of overlying strata for gob-side entry retaining in 1000 m deep mine with direct thick and hard roof

ZHAO Yiming，ZHANG Nong，ZHENG Xigui，LI Baoyu

2015, 32(5):  714-720. 

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The stress environment of surrounding rock in gob-side entry retaining has been deteriorated by mining field large area hanging, longer roof hanging along gob-side under direct thick and hard roof condition. In order to solve the problem, the characteristics of strata behaviour of gob-side entry retaining with direct thick and hard roof in over 1 000 m deep coal mine have been analyzed in this paper. The structural optimization technology of overlying strata for gob-side entry retaining with hard roof condition has been proposed, which is compounded by roof caving optimization advanced the working face and pressure relief for hanging roof structure cutting along gob-side using the deep hole presplitting blasting. Simultaneously, the relationship between the length of roof hanging along gob-side and the strength acted on filling wall has been obtained, and the paper has pointed out the reasonable length of roof hanging along gob-side for long-term stability of the surrounding rock in gob-side entry retaining is under the condition of no more than 12 m. The related research results have been successfully applied in gob-side entry retaining of 14-31010 working face in Pingdingshan Twelve coal mine, and have provided reference to the implementation of gob-side entry under the same conditions.

Study on mechanism of the discontinuous “double shell” surrounding rock control in deep soft-engineering rock roadway

YANG Bensheng，WANG Zhongyong，JIA Yongfeng，SUN Lihui，GAO Bin

2015, 32(5):  721-727. 

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When the deep roadway has been deformed seriously, it is difficult for the traditional support to achieve effective control of roadway surrounding rock. Taking the distortion and breakage of the whole section of the New South total return air roadway of Tao’er coal mine as the research object, the damaged condition and the factors that cause the damage have been analyzed through the field investigation and monitoring. The study has shown that the reason of the distortion and breakage of the whole section of roadway is that firstly surrounding rock shear and breakage occurs under the effect of high ground stress, and then the surrounding rock gets further expansion break and creep under the effect of gas pressure and water conditioning. The paper has also analyzed the control mechanism of discontinuous “double shell” surrounding rock with the application of discontinuous "double shell" surrounding rock control theory. Additionally, this study has helped to build the key technology of the control of discontinuous “double shell” surrounding rock as the U-shaped steel (external stress supports shell)+flexible plate (soft layer)+grouting anchor bars(internal stress reinforces shell), and finally obtained good supporting effect.

Dynamic caustics model experimental study on the defects extension of roadway surrounding rock when blasting excavation

GUO Dongming，YAN Pengyang，YANG Renshu，ZUO Jianping，YUAN Baosen，ZHAO Wei

2015, 32(5):  728-734. 

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In order to analyze the influence of the blasting dynamic load on defects extension of roadway surrounding rock in different locations, the explosion load system using dynamic reflected caustics has been used to conduct the organic glass model experimental study. The experimental results have shown that under the influence of dynamic load the vertical crack at the top of the roadway is easier to extend than others, then are the inclined cracks at the arch and the corner，and the last ones are the horizontal cracks with the data of cracks propagation length of 31，17，20 and 6 mm respectively. The value of the displacement of crack propagation has a direct relationship with the value of the stress intensity factor and we can see that the value of the stress intensity factor of the vertical crack at the top of the roadway is greater than that of other three cracks, then is the value of the inclined cracks at the arch and corner and the value of the horizontal crack is at the minimum level. The above research results have positive influence on reducing the disturbance and damage of the blasting dynamic load on surrounding rock, and on saving the cost of surrounding rock supporting, ensuring construction safely and rapidly.

Reinforcement mechanism and control technology with two-ended cables of roadway and chamber groups influenced by mining

WEI Sijiang，SONG Changsheng，YANG Yushun，SUN Chuang

2015, 32(5):  735-740. 

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According to the problem of creep damage and reinforcement of roadway and chamber groups influenced by mining with high abutment stress and weak adjacent rock in Hebi 9th Colliery, strengthening method has been proposed, characterized with full cross-section, shallow-deep hole grouting and two-ended cables. The instability mechanism of roadway and chamber groups with high abutment stress has been studied by means of analogue simulation. The study has shown that as the top pressure increases, displacement of chamber rock pillar increases; bearing capacity of pillar decreases; loads of two-ended cables increases at first, then adjusts continuously in wavy shape. Two-ended cables are vital to the bearing capacity and compressive stress increase of wall surface. Narrow rock pillar is seriously damaged by high abutment stress. Overall movements happen in wall anchorage body. The industry tests have shown that the two-ended cables can effectively help to control the stability of pillar and adjacent rock.

Numerical simulation and analysis of buffering effect of dynamic disturbance of new reinforcement structure on deep roadway

WEI Mingyao，WANG Enyuan，LIU Xiaofei

2015, 32(5):  741-747. 

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This paper has conducted an analysis of the attenuation characteristic of the stress waves when propagating in different wave impedance interfaces between media based on stress wave theory. Subsequently, the theoretical relationship between energy attenuation and wave impedance ratio has been established. Based on the results of the analysis, the paper has put forward a new type of reinforced support structure, namely, the reinforced annular region. Specific reinforcement methods for the annular region are adopted within the roadway surrounding rock to reinforce the rock mass strength and then form the high-intensity annular reinforcing structure. This structure has not only enhanced the overall strength of the surrounding rock, but also significantly attenuated the energy of the stress wave in the reinforced annular region. Thus, the damaging effect on the roadway has been reduced. In order to further verify the results, a numerical model has been built using the software FLAC3D for a comparative analysis of the damage situations via dynamic disturbance, with and without the setting of the reinforced circle on the roadway, and the energy attenuation characteristics of the stress wave has also been tested. The results have indicated that the stress wave shows clear energy attenuation with the reinforced circle, and the damaging effect on the roadway is reduced. The theoretical analysis and numerical simulation results have both verified that the reinforced structure effectively can improve the stability of the surrounding rock and reduce roadway deformation and damage through its dual function of strengthening the support and attenuating the dynamic disturbance. These features have presented potential applications for deep surrounding rock control technology.

Theoretical and experimental research on the vibration characteristics excited at the end of pre-stressed rock-bolt

LI Qingfeng，ZHU Chuanqu

2015, 32(5):  748-752. 

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In order to improve the random and non-destructive dynamic detection accuracy of pre-stress of rock-bolt, according to pre-stressed rock-bolt mechanical characteristics loaded on the surrounding rock, the mechanical model of non-destructive dynamic detection of pre-stress of rock-bolt has been firstly put forward. Secondly, based on elastic dynamics and structural dynamics, the theoretical analysis of vibration mechanical model of pre-stressed rock-bolt has been presented when it is stimulated at its outer end, and the pre-stress formula of pre-stressed rock-bolt has been obtained. Finally, with the simulation of surrounding rock with concrete block, and anchored resin rock-bolt in the reserved hole of concrete block, the non-prestressed and prestressed rock-bolt have been detected by non-destructive dynamic detection instrument. The result has shown that the cantilever dynamics model is consistent with vibration mechanics characteristics of pre-stressed rock-bolt when stimulated at its outer end, and that test error basically meets the requirement of the field.

Sealing mechanism of the grouting bolt hole with pre-tensioned cable and design of a new sealing device in the roadway floor

LIU Shaowei，CHANG Jianchao，ZHANG Hui，ZHU Qiankun

2015, 32(5):  753-759. 

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As the mining depth increases, the floor heaves has become the main factor which influences the safety production and economic interest of the mine, and the pre-tensioned cable bolt with grouting is an effective way to deal with the floor heave. Because of the lack of professional and effective grouting sealing devices, the procedure of grouting with pre-tensioned cable bolt has become complicated, ineffective and unqualified. The sealing mechanism of the grouting hole with pre-tensioned cable bolt has been analyzed in this paper. The K-ε two-dimensional turbulence model has been adopted to conclude the flow field distribution principle of slurry under different sizes of sealing length and sealing annulus. It has analysed the flow velocity and pressure variation characteristics of slurry in the sealing annulus. Then the relatively reasonable sealing length and sealing annulus have been determined. Fluid theory has been used to calculate the slurry loss and to find out the optimum size of sealing length and sealing annulus, which has provided theoretical basis for the structure size design of the sealing device and the proportioning of sealing materials in the slurry pocket. Using the research result, it has developed a new sealing device for the grouting bolt hole with pre-tensioned cable.

The analysis of end anchoring-grouting prestressed anchor loading and support design with bed separation considered

GU Shuancheng，DING Xiao

2015, 32(5):  760-764. 

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Roof bed separation often occurs due to the deformation incoordination of surrounding rock in the process of the excavation of mine roadway. Bed separation has effect on the bolts, and the estimation of the influence will directly affect the safety of support systems. The stress distributions of systematic bolt has been obtained, considering the pre-tightening force of end anchoring-grouting bolt and the additional stress caused by roof bed separation. The results have shown that under the influence of roof bed separation, anchorage axial force and shear stress will all increase．Anchor failure happens easily when bed separation value is too large, which will produce the potential safety hazard. Finally, the effects of bed separation have been taken into consideration in the bolting design, and a new bolt design concept has been provided. It has been proved that the bearing capacity design method after considering roof bed separation is safer and more reasonable．

Study on migration characteristic of boring mud in roadway floor anchor wire hole and its field test

ZHANG Hui，CHENG Lixing，CHANG Jianchao

2015, 32(5):  765-770. 

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To solve the problem of drilling anchor holes into the roadway floor, migration characteristics of the reverse circulation drilling process of boring mud have been analyzed. The analysis has shown that the interaction of boring mud three-field is the primary cause of restricting floor anchor wire hole quickly drilling, and pump suction reverse circulation drilling that can be effectively prevented by boring mud three-field forming has been put forward. Using principles of solid-liquid fluid mechanics, mechanical formula of flushing fluid along hydraulic loss and slag drilling fluid return velocity has been successfully deduced. According to the field practice, the relationship between floor anchor wire hole pump suction reverse circulation drilling depth and drilling pump on vacuum degree and slag drilling fluid return velocity, and drilling slag volume content has been obtained. The result has shown that pump suction reverse circulation faster penetration of floor anchor hole is feasible. A set of pump suction reverse circulation drilling system has been developed, and floor anchor wire hole drilling and slag discharge operation at the same time have been realized. Field test has shown that effective time of drilling depth of 5.6 m floor anchor wire hole can be controlled within 30 min. The difficult problem of floor anchor wire hole deep hole drilling has been solved, and the work environment has been purified.

Study on optimization of rapid combined excavation cutting sequence in half-coal rock roadway

WANG Weiming，LYU Xianzhou，QIN Wenlu

2015, 32(5):  771-777. 

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In order to solve the coal mine engineering problem of the rapid combined excavation in thin seam half-coal rock roadway, aiming at the design and optimization of combined excavation cutting sequence, the numerical model for analyzing the stress evolution of surrounding rock, the shape presentation of shear strain increment and shear strain rate under different excavation sequence has been established by using three-dimensional fast Lagrangian method in this paper. The displacement and rupture range analysis model of different excavation scheme has also been established based on the grey relation theory, and the correlation degree of each scheme has been obtained with the result of 0.63, 0.76, 0.81 and 0.73. Finally an optimal combined excavation cutting scheme has been determined based on the numerical simulation and theoretical calculations, which has been verified by the concrete project. The engineering practices have indicated that the combined excavation cutting sequence of “down-up, right-left” can achieve the optimal combined excavation in half-coal rock roadway. Meanwhile, the monitoring results have also proved its rationality and feasibility.

Analysis on rock plastic zone displacement of deep buried underground chamber based on generalized Hoek-Brown criterion

CAI Haibing，CHENG Hua，RONG Chuanxin

2015, 32(5):  778-785. 

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Generalized Hoek-Brown criterion is indicated as a dimensionless quantity; on this basis, elasto-plastic analytical method of circular underground chamber in uniform stress field has been established. According to the following three kinds of circumstances: 1) without considering rock dilatancy and elastic deformation in plastic zone, 2) considering rock dilatancy and constant elastic deformation in plastic zone, 3) considering rock dilatancy and varied elastic deformation in plastic zone, surrounding rock plastic zone displacement of deep buried underground chamber has been comparatively analyzed for different quality rock mass. The results have shown that surrounding rock plastic zone displacement is the maximum under the circumstance of considering rock dilatancy and varied elastic deformation in plastic zone. For soft rock chamber in poor and average quality rock mass, rock dilatancy and varied elastic deformation in plastic zone must be considered in the process of analysis on surrounding rock plastic zone displacement. For chamber in good quality rock mass or hard rock chamber, rock dilatancy and elastic deformation in plastic zone may not have to be considered.

Infrared radiation portentous characteristics of rock burst in roadway

ZHANG Yanbo，LI Jian，LIU Xiangxin，TIAN Baozhu

2015, 32(5):  786-792. 

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Selecting the infrared thermal imager CAM SC3000 produced by America as observation method, an experiment was carried out to simulate roadway rock burst under different horizontal stress by using the granites with hole. Combined with numerical simulation, the stress distribution and infrared radiation temperature characteristics were studied during the process of rock burst. The results show that the ratio of axial stress and horizontal stress decreases with the increase of horizontal stress, and the greater the horizontal stress is, the higher the maximum principal stress of rock burst is. The average infrared thermal temperature (AIRT) in the left and right sides of the hole suddenly increase or slightly decrease and then transfer to increase, and the corresponding fracture mechanism is the compressively- sheared fracture form and the composite form with early tensile fracture and late compressively- sheared fracture. The main fracture zone extends along the high temperature abnormal stripe on the left and right sides of the hole. During the rock burst process, the increasing extent of temperature above and below the hole is lower than that in the left and right sides of the hole, that is, the temperature increasing extent above and below the hole is relatively stable. Meanwhile, the AIRT above the hole is higher than that below the hole. Moreover, the greater the horizontal stress is, the higher the average infrared radiation temperature around the hole is.

“O-X” failure pattern of roof and strata-pressure behavior under complex geological conditions

LIU Honglei，YANG Tianhong，ZHANG Penghai，LI Yang，QIN Tao，YU Qinglei

2015, 32(5):  793-800. 

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In this paper, on-site monitoring, theoretical analysis and numerical simulation were used to study the strata pressure behavior and “O-X” failure law of roof under complex geological conditions in Da’anshan coal mine. Roof caving characteristic and strata pressure behavior in No.13 coal face of Da’anshan coal mine were studied through ground pressure monitoring system. Additionally, based on the field monitoring data, numerical model was established to study the formation, evolution and fracturing law of roof plastic zone during mining process. The results show that the support resistance in the middle of working face is significantly greater than those in the upper and lower parts. During the weighting period, the average length of stress concentration in the gateways is 12.17 m and 9.46 m respectively ahead of the face, and the corresponding maximum pressure is 24 MPa and 23.57 MPa respectively. In addition, the“O-X”fracture structure was obtained through numerical simulation and theoretical analysis. The first weighting and periodic weighting steps obtained by numerical simulation are basically consistent with the on-site monitoring.

Critical support resistance calculation in the working face of improving upper limit with hard roof and prevention countermeasures of support crushing

LI Yingfu，HUA Xinzhu，YANG Ke，LI Zhihua

2015, 32(5):  801-807. 

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To avoid support crushing disaster again in No. 1602(3) working face of improving upper limit with hard roof in Panyi coal mine, Huainan, based on the similar simulation results, the fracture characteristics of overlying strata were studied, the structure mechanics model of overlying strata were established, the critical support resistance was deduced, the instability criterion of support crushing was determined, and the factors influencing critical support resistance of support crushing were further analyzed. The results prove that these measures such as reducing working face length, lowering mining height, keeping the integrity of immediate roof, preventing large hanging roof in the gob, strengthening the coal wall, hydrophobic step-down before mining, etc. can be in favor of the stability of support in the working face of improving upper limit with hard roof. On this basis, further prevention countermeasures of support crushing such as forced caving, high-grade conventional mining, reasonable equipment selection, etc. were proposed, which were applied to the modified No.1602(3) working face successfully, and good economic benefits were obtained.

Research on strata behaviors and variation characteristics of overburden strata of fully mechanized top coal caving in mining efflorescent oxygenized zone

TIAN Duo，ZHAO Qifeng，SHAO Guoan，SHI Haoyu，LIU Gang，SHI Laiyang

2015, 32(5):  808-813. 

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According to the site measured strata pressure information of the coal mining face in mining efflorescent oxygenized zone of coal seams in No.3 Coal Mine of China Coal Pingshuo Group Co. Ltd， the paper has discussed the obvious sectional variance features occurring in top coal and the overlying strata above mining face in efflorescent oxygenized zone, such as loose strata structure, low overburden rock strength, high plasticity property, strong hydrophilicity, serious sliming, and the obvious decrease of stability performance and bearing capacity. The mine strata-pressure behaviors of passing the efflorescent oxygenized zone of coal seams are mainly reflected in the following three aspects: periodic weighting distance shortened, both the maximum working resistance of hydraulic power support during roof pressurized period and the average working resistance during non-pressurized period increasing, and support dynamic load coefficient decreasing during passing the efflorescent oxygenized zone compared with outside the scope. The mechanism of the sectional variance in strata behaviors have been analyzed by using geological mechanics, from which the paper has shown that the geological incentive of the strata-pressure behaviors variability is the new type Soft Cushion effect caused by soft-broken surrounding rock，fractured and sliming rock mass and float coal auxiliary compression under the floor. The Soft Cushion effect will lead to lower working resistance of the supports. Then the characteristics of the support operation of working face have been analyzed and the adaptability of the powered supports has been assessed.

Water-preserved mining evaluation in shallow seam with sandy mudstone roof

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

2015, 32(5):  814-820. 

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Focusing on widely distributed sandy mudstones above upper No.2-2 coal seam in Gaojialiang mine, Ordos, the microscopic structure and mineral composition of sandy mudstones deposited during different periods were tested, and the fractured zones above working faces with different geological conditions were further detected. The results show that particle volume of sandy mudstone in Jurassic Zhiluo and diazepam group is small, with the characteristics of point contact between particles, low voidage, high content of montmorillonite, swelling with water, poor cementation, easy broken, and water preventing ability after rock fractured. Evaluation model of water-preserved mining in shallow seam with the sandy mudstone roof was constructed, two basic conditions of water preserved mining were obtained, and the evaluation method was put forward. Industrial test shows that the evaluation results are concordance with that of field practice.

Water loss settlement simulation of thick unconsolidated confined aquifer layer

XU Liangji，ZHU Nan，MA Rongzhen，LIU Xiaopeng

2015, 32(5):  821-826. 

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To reveal the mechanism of surface movement and deformation caused by water loss in thick unconsolidated confined aquifer during coal mining, based on specially designed experimental equipment, the water loss settlement experiment of unconsolidated confined aquifer was carried out, and the effect mechanism of confined water loss in unconsolidated layer to surface subsidence was analyzed. The results show that consolidation settlement of soil can be appeared due to water loss no matter with pressure or not, which is also the reason for consolidation and compression deformation of aquifer. Under the same conditions, the deformation of soil with fine particle size is larger than that of soil with coarse particle size.

Coal wall stability and grouting reinforcement technique in fully mechanized caving face during topple mining

YANG Shengli，KONG Dezhong，YANG Jinghu，MENG Hao

2015, 32(5):  827-833. 

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Probed into the general mechanism of the coal wall failure in thick coal seam, combined with the main failure form of coal wall in 8101 mining face of Ruilong mine, the mechanical model of rib spalling during the topple mining was established, and the sensitivity analysis was also implemented to study the factors influencing the coal wall stability. The results show that the mining height, confining pressure, support strength, angle of topple mining, strength of coal, etc., have a great influence on the stability of coal wall, and reducing the mining height, improving the support strength, and grouting reinforcement of coal wall are the most effective measures to prevent the rib spalling of coal wall. The reasonable drilling diameter of grouting reinforcement was further studied through theoretical analysis and UDEC numerical modeling. As a result, the grouting effect with 15 mm in borehole diameter is the best to control rib spalling of coal wall.

The research of rock dynamic fracture parameter under the action of impact load

SONG Yimin，YANG Xiaobin，YANG Shengxuan，WANG Qian

2015, 32(5):  834-839. 

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An experimental research of rock dynamic fracture parameter under the action of impact load with the rectangular granite specimen with pre-cracks of Type I has been conducted. The test material is loaded by self-developed adjustable speed drop hammer impact tester which can realize low & medium impact loading speed；the data is recorded by data collecting system set up by high-speed cameras, and the data of specimen surface speckles images in the dynamic fracture process of crack is analyzed by using digital speckle correlation method. The quantitative results of displacement field evolution, the dynamic fracture of crack tip opening displacement, the speed of the crack growth and stress intensity factor of the dynamic fracture have been obtained. The experimental results have shown that the crack tip stress intensity factor increases after drop hammer contacts with the rock specimen, and when the stress intensity factor reaches a certain value, the prefabricated crack initiation and subsequent stress intensity factor of crack initiation is greater than the initial crack stress intensity factor.

Study of overlying strata creep affected by seepage in backfilling mining process

PU Hai，CAO Lili，QIU Yanyong，QIU Peitao

2015, 32(5):  846-852. 

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Because the creep properties of overlying strata will be affected by the groundwater seepage in the backfilling mining process, which will finally affect the long-term stability of the overlying rock and surface. Starting from the general solution of the rheological mechanics, this paper has derived the stress equilibrium equation of the rock under the action of stress and water pressure according to the equation of hydrostatic equilibrium, the principle of effective stress, and the geometric equations based on the Burgers model in the classic rheology. Meanwhile seepage field control equation has been acquired according to the Darcy’s law and the seepage field equation of continuity. Finally the seepage- creep coupling mathematical model has been founded. Besides, based on the actual geologic conditions of some mine, the paper has also systematically studied the overlying strata creep rules under different mining methods and different pore water pressures according to the derived mathematical model of seepage-creep coupling and on the computing platform of Comsol Multiphysics.

Experimental study on the seepage characteristics of cemented broken mudstone

YU Bangyong，CHEN Zhanqing，WU Yu，ZHANG Shaobo，YU Linli

2015, 32(5):  853-858. 

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Under the action of corrosion, abrasion and erosion from groundwater, the cementation structure in Karstic collapse column is broken and some particles are lost. As the action continues for a certain time, the seepage burst will occur. In order to study the water inrush mechanism of Karstic collapse column, the original designed compacting device and seepage experiment system of broken rock have been used to complete the seepage experiment of cemented broken mudstone. The influence of cementing material, water pressure, broken mudstone size distribution and initial porosity on seepage characteristics has been analyzed. The results have shown that: 1) With cementing strength increasing, the duration time of seepage burst gets longer; When the cementing material is cement, the seepage capacity tends towards stability without burst. 2) With the water pressure increasing, the duration time of seepage burst gets shorter by an exponential function. 3) With the Talbol power exponent increasing, the rock particles in big sizes get more and the water-blocking ability strengthens. 4) With initial porosity increasing, the seepage capacity strengthens. The duration time of seepage burst gets shorter through an exponential function.

An experimental research on gas permeability of coal gangue backfilling body under different parameters

ZHU Chuanqu，KANG Furu，XIE Donghai，OU Yi，YANG Dangwei

2015, 32(5):  859-863. 

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In order to study the gas permeability of coal gangue backfilling body, based on the pressure- difference method and Darcy's law, an experimental system for measuring the gas permeability has been proposed. And a series of experiments under various particle gradation，different surrounding rock pressures and different gas concentration have been conducted by using the system. The results have shown that the gas permeability coefficients of coal gangue backfilling body measured by the experiment are in the interval of [0.649，3.206] m2/(MPa2·d)，which belong to the appropriate scope of gas drainage，and that the coal gangue backfilling body has good air penetrability. Based on the results of the experiments, the paper has put forward various methods such as appropriate increase of the grain size of coal gangue backfilling body and the ventilation quantity between working face ends, and decrease of the bearing capacity of coal gangue backfilling body and the gas concentration of packing area to increase the gas permeability of coal gangue backfilling body, and the experimental results have provided theoretical guidance for safe and highly effective gangue backfilling technology development under the circumstance of protective layer mining.

Numerical simulation and application of controlling gas accumulation in upper corner of drainage instrument and tail roadway

WANG Kai，JIANG Shuguang，MA Xiaoping，WU Zhengyan，SHAO Hao，ZHANG Weiqing，PEI Xiaodong

2015, 32(5):  864-870. 

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In order to solve the problem of fluctuation overrun of gas in upper corner of S5-2 working face, the paper has analyzed some elements like coal mining technology and periodical weighting to expound the cause of the upper corner gas fluctuation overrun. The method that the drainage device is used to change the corner eddy current field has been provided to optimize the tail-road configuration and to change the upper-corner gas vortex field with drainage instrument and to control the fluctuation overrun of gas accumulation efficiently. The Fluent numerical simulation, establishing the upper corner gas air-eddy current field model, has been used to simulate the effect of using the different drainage volume of drainage device to change the upper corner air-gas vortex, and the distribution characteristics of wind speed, wind pressure of local wind. And the ventilation effects for different tail step distance and air distribution numerically have been simulated to analyze the distribution characteristics of wind speed, wind pressure and gas concentration in different places in the working face of configuration and the goaf air flow-gas flow field mode. Combined with the simulating results, the best air distribution amount and step distance of tail roadway in S5-2 working surface and the best method of drainage instrument configuration have been determined. The monitoring results have shown that it has obvious effect on the gas fluctuation limit in upper corner.