Journal of Mining and Safety Engineering

Study on safety evaluation method of bolting and wire mesh systems in coal roadway

HAN Li-jun, MENG Qing-bin, WEI Zhong-min, SUN Chang-xing, SHI Gao-peng

2013, 30(6): 791-798.

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To solve some problems of bolting-wire mesh support system in the coal roadway, we have put forward a set of evaluation theories and methods of “monitoring data - inverse analysis method - security alert value - predictive analysis - evaluation system”. That is, using initial fuzzy system to classify surrounding rocks of coal roadway supported by bolting-wire mesh, then using inverse analysis method to obtain mechanical parameters of roadway surrounding rock mass. And then with the numerical analysis method and theoretical calculation, the roadway roof abscission layer, convergence deformation, the numerical and analytic solution of anchor has been obtained. Consequently, security alert value is determined. Based on monitoring data, the nonlinear fitting technology is used to forecast and analysis supporting structure deformations and stability parameters of coal roadway. Finally, on the basis of VB programming language, a system of coal roadway surrounding rock classification, security alert value, monitoring data prediction and safety evaluation is set, and a safety evaluation system of coal roadway supported by bolting-wire mesh is constructed, which can realize real-time master sup- porting structure deformations and stability parameters of coal roadways. It is very helpful to increase information construction and management level of coal roadways with bolting-wire mesh support.

Field research on long-term bearing capacity of strip pillar

WANG Chun-qiu, GAO Li-qun, CHEN Shao-jie, WANG Hai-long, LIU Jiang-bo

2013, 30(6): 799-804.

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In order to study the long-term bearing capacity of strip pillar, a strip pillar of Daizhuang coal mine is monitored. A strip pillar stability state structure model is established according with the engineering practice of Daizhuang coal mine, and the relationship between the stress of pillar and manometer reading is determined. The strip pillar is monitored with drilling pressure meter and automatic monitoring system for a long time. Monitoring results show that the edge of pillar can be destroyed easily, and the actual maximum bearing capacity of the part which is 1，2，3 m away from the edge is respectively 6.31，6.96，9.76 MPa; the actual bearing capacity at the part which is 5 m away from the edge is greater than 11.90 MPa. In the end of field research, the maximum bearing part is 6~8 m away from the edge of strip pillar, and the bearing capacity of the central part of the 70 m-width pillar is smaller. The bearing shape of whole pillar presents as typical saddle during the whole period of the research, which indicates the pillar can keep stable for a long time.

Experimental study on structural property of contractible concrete-filled steel tube support

WEI Jian-jun, JIANG Bin-song

2013, 30(6): 805-811.

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Experiments on the concrete-filled steel tubular (CFST) support under symmetrical and unsymmetrical in-plane loadings have been carried out. Based on the experimental results, this paper studies the deformation, strain, the increasing resistance law of contractible joint and ultimate bearing capacity of CFST arch support. The results show that the CFST support has good elastoplasticity and carrying capacity due to the cooperative work of steel and concrete. Initial imperfection or partial weakening of the support is a major reason for the destruction of the support. The increasing resistance curve of contractible joint can be divided into three stages. The contractible joints should be tightened in a timely manner in accordance with the field monitoring for the bearing capacity fluctuated after slip. Finally, the characteristics of bearing and deformation of CFST arch support are analyzed with ABAQUS software, and the simulated results are fairly close to the experimental results.

Study on affecting factors of soft rock deformation with orthogonal numerical simulation test

FU Yu-kai, JU Wen-jun

2013, 30(6): 812-816.

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The paper studies the impact of different parameters on two-sided displacement and convergence between roof and floor by using orthogonal numerical simulation test method. Six factors such as roadway width, roadway height, burial depth, lateral pressure coefficient, strength of surrounding rock and support strength, and three levels of orthogonal experiment method are selected to conduct FLAC numerical simulation test. The simulation results by variance analysis method is analyzed and industrial tests in the underground is conducted. The results show that the six factors have some impact on the two-sided displacement and convergence between roof and floor, but the impact levels are different. The order of the magnitude of factors affecting two-sided displacement is strength of surrounding rock, support strength, burial depth, lateral pressure coefficient, roadway height, roadway width; the order of the magnitude of factors affecting convergence between roof and floor is strength of surrounding rock, support strength, burial depth, lateral pressure coefficient, roadway width, roadway height. Test results tested in the underground are well consistent with numerical simulation results, which indicates that there are certain degree of reliability to guide field support work with orthogonal simulation method.

Mechanical performance testing and analysis of steel tuber confined concrete supports in roadway supporting

LI Xue-bin, GAO Yan-fa, YANG Ren-shu, QU Guang-long, HE Xiao-sheng, XUE Hua-jun

2013, 30(6): 817-821.

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Steel tuber confined concrete (STCC) supports, as a new support form, has been gradually applied in underground roadway support. In this paper, the mechanical properties of STCC supports were comprehensively analyzed by theoretical analysis, laboratory tests and numerical simulations. Based on the ultimate bearing capacity (UBC) formulas of STCC axial compression short columns, UBC of short column can reach 1 115.5 kN, which is greater than the UBC sum of the hollow steel tube and plain concrete short column. In the support loading test, the support is affected by pole instability duo to loading constraint conditions, while the strengths in various parts of support are different, which leads to the fact that UBC of the tested supports is 1.35 times than that of short column. In numerical simulation of roadway model supported by circular STCC supports, both the yield load and ultimate load of supports are over 2 times of the UBC value of short-column．In addition, large plastic deformations of supports have been produced, and the deformation rate is close to 9%. Therefore, duo to the high bearing capacity of STCC supports, as well as the advantages of large deformation and yielding support, it is particularly suitable to be applied in soft rock roadway support and deep roadway support.

Evolution characteristics of deformation and energy fields during coal pillar instability

SONG Yi-min, YANG Xiao-bin

2013, 30(6): 822-827.

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In this paper, based on the uniaxial compression test of coal samples, the evolution characteristics of deformation and energy fields during coal pillar instability process were studied. Meanwhile, the specimen surface speckles images were recorded by CCD camera. Combined with the monitoring results of coal samples’ whole deformation and failure process by using the digital speckle correlation method, the generation and evolution of deformation localization in coal pillar, as well as the characteristics of coal pillar instability in each stage were systematically analyzed. Then, the energy evolution during coal pillar instability process was calculated. The results show that the coal pillar instability can be divided into two types: unstable propagation of fracture inner coal piller and unstable sliding of weak plane inner coal piller. The energy release and accumulation patterns during loading process of coal pillar are mainly controlled by the final instability modes. Comparatively speaking, the energy release rate during the weak plane unstable sliding inner coal piller is relatively small, while the energy release rate during the fracture unstable propagation is larger.

Measurement of loosened surrounding rock scope in the rectangular roadway and its control techniques research

YU Yuan-xiang, GU Shuan-cheng

2013, 30(6): 828-835.

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For the inefficiency of the loose rock theory and numerical simulation in the study of loosened surrounding rock scope in the rectangular roadway, based on the data obtained from on-site measurement of loosened surrounding rock scope in the main roadways of Wangcun mine, Wangxie mine, Erkuang mine as well as Dongjiahe mine by means of multipoint displacement and drilling peeping, this paper established different prediction formulas of the loosened surrounding rock scope with roadway depth, section size, surrounding rock strength as well as various factors under different lithologies. The results show: 1) when the section size of the rectangular roadway is constant, the average thickness of loosening in the roof has a positive growth with the roadway depth and anti-growth with compressive strength of the roof; 2) when the depth of the rectangular roadway is constant, the average thickness of loosening in the roof has a positive growth with span-height ratio of the roadway and anti-growth with tension and compression strength ratio of the roof rock; 3) when the lithology of the sides is constant, the average thickness of the loosening in the sides rock of the rectangular roadway has a positive growth with the depth and proportional positive growth with the span of the roadway. Field supporting test of the transport trough was conducted in the 13503 coal face in Wangcun mine according to the obtained prediction formula, which achieved good effect in controlling the surrounding rock.

Surrounding rock control optimal design of large section roadway in soft coal seam

LIU Jin-rong, KANG Qing-tao

2013, 30(6): 836-840.

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Affected by complicated factors such as large section, low strength of coal mass, high in-situ stress, rich water roof and Mudstone floor characterized by rheological, swelling and softening property, the roadway in Ma Jialiang Mine soft coal seam encounters heavy rock surrounding support problems of roof sag and floor heave. Consequently, the safe and orderly production was affected seriously. Taking the main air return way as a primary research object, the paper has studied the law of surrounding rock deformation and failure, reasonable section size and shape, support parameters and floor heave control method by means of field measurement, theoretical analysis, numerical simulation and so on. The research shows that micro cambered arch roof, drain-pipe installed in roof, inverted-arch floor, net and bolt support of whole section are the optimum combination of section form and support scheme. The field application tells that the optimized air return way surrounding deformation can be controlled effectively, which meets the requirements of keeping it stable for a long period. The achievements of this research will offer useful data for large section roadway support in soft coal seam.

Experimental research on failure characteristics and bursting liability of rock-coal-rock sample

MU Zong-long, WANG Hao, PENG Peng, LIU Zhen-jiang, YANG Xiao-chen

2013, 30(6): 841-847.

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In order to determine the bursting danger of mining zone, and to solve the limitation of coal and rock's bursting liability evaluation criterion, the stiffness values of coal’s post-peak and rock’s unloading process are used to evaluate the steady and unsteady failure of rock-coal-rock sample based on the analysis of deformation, acceleration, stiffness and energy variation. The research results indicate that rock-coal-rock sample’s failure state is determined by the contrast relation of coal’s post-peak stiffness and rock’s stiffness. There is a point S on the coal’s stress-strain curve during the unloading process where the stiffness changing ratio satisfies the relation of , after which the rock-coal-rock sample’s shall not keep the balance state, and the sample's failure will convert from stable to instable state. The parameter which is the ratio of the energy that roof and floor releases to that of coal releases is used as the index of bursting liability of rock-coal-rock sample. The results of seven sites’ samples from 2 mines indicate that there are 2 samples’ bursting liability is under the influence of roof and floor attribution. The model of rock-coal-rock sample can reflect the bursting liability of in-situ surrounding rock more accurately than that of only coal.

Control principle and pressure-relief technique of rock burst occurred in roadway floor

CAO An-ye, ZHU Liang-liang, DU Zhong-yu, LIU Jian-gang, WANG Hao, WANG Yi

2013, 30(6): 848-855.

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The occurrence intensity and damage degree of rock burst occurred in roadway floor of underground coal mines becomes more serious as the mining depth increases in China. In this paper, the inducement mechanism of floor burst was analyzed, and the corresponding control principle was put forward, that is, the burst-inducing condition was decreased by changing the bending strength of roadway floor. Additionally, FLAC3D was adopted to simulate and compare the pressure-relief effects of different control measures implemented in coal-floor roadway and rock-floor roadway, respectively. The results show that the pressure-relief effect of the control method by combination of large-diameter borehole and pressure-releasing groove on coal-floor roadway is more effective, while the combination of large-diameter borehole and releving shot on rock-floor roadway can achieve better pressure-relief effect. The research results in this paper can provide theoretical reference for floor burst control in underground mining.

The research on the coal wall stability mechanism in larger height coal seam with a stratum of gangue

YANG Jing-xuan, LIU Chang-you, WU Feng-feng, YANG Yu

2013, 30(6): 856-862.

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The integrated research methods are adopted to analyze the coal wall stability for the issue of the hard gangue effect in full height mining face by the means of the theoretical analysis, indoor experiments and field measurement. The coal wall spalling model and the stable conditions are proposed, and the rib spalling mechanism in stratum of gangue is studied. The results show that: the compressive strength of the coal block in gangue or superimposed coal sample can be increased compared with the pure coal block; the axial deformation of the pure coal block or superimposed coal sample is larger than the coal block in gangue; the overall stability of the coal wall can be effectively improved in the coal seam with a stratum of gangue; the coal height has greater impact on the coal wall stability——the higher of the coal face, the easier for the coal wall instability under the same external load conditions; the coal face stability condition is given considering the differences of the continuous degree between the field coal body and indoor coal sample. The field measurement indicates that the rib spalling is more stable of the No.28202 coal face in context of the actual production in Dong-qu coal mine, and the rib spalling occurs mainly in the upper position of the No.8 coal seam. The coal face production conditions have been improved base on the low degree of rib spalling.

Stability analysis of large-scale mined-out area and its control methods in Paomaping lead-zinc deposit

ZHOU Zong-hong, HOU Ke-peng, REN Feng-yu

2013, 30(6): 863-867.

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This paper investigates the roof strata stability of complicated mined-out areas and determines the reasonable control methods. Taking the Paomaping Lead-zinc deposit as the engineering background, the theoretical analysis, field investigation and laboratory mechanical experiments are carried out. The critical collapse area of goaf roof is calculated based on the equilibrium arch theory. In view of above researches, using three-dimensional finite element numerical simulation method, the deformation and failure mechanism of roof strata in mined-out area is analyzed and the corresponding control methods are put forward. The results show that the critical caving equivalent circular area of mined-out area is 6 191 m2, and the existing exposed area of the mined-out area is close to the critical failure value and its exposed area should be effectively controlled. The exposed area and span of the mined-out area are the main factors affecting the roof stability. With their expansion, the tensile stress appears in the roof, resulting in unstable failure. Forced caving of roof and surrounding rock will obvi- ously decrease the stability of mined-out area, inducing the roof strata instability. Waste rock backfilling of mined-out area can effectively control the strata deformation, improving the rock mass stress and roof stability.

Mechanism analysis of restraining surface cracks and protecting Tetraena mongolice maxin with backfilling mining

DING Yu-long, ZHOU Yue-jin, XU Ping, PENG Gang, CAO Zheng-zheng

2013, 30(6): 868-873.

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Tetraena mongolice maxin plays an irreplaceable role in ecological system stability and environment protection as the constructive species in desert areas. By investigating and analyzing on the growth characteristics of Tetraena mongolice maxin roots, this paper puts forwards that Tetraena mongolice maxin fibrous root is prone to be broken for the surface deformations and cracks induced by underground caving mining. And mining changes the water retention property of the soil in the region of root system, which affects the growth and reproduction of Tetraena mongolice maxin. In this paper, the calculating formulas of surface tensile strain are deduced and the characteristics of surface cracks are analyzed based on mining subsidence theory. Then the corresponding relationship between mining thickness and surface tensile strain are concluded. Based on the equivalent height theory of backfilling mining, the corresponding relationship between equivalent mining thickness with surface fracture development and broken roots of Tetraena mongolice maxin is established. Namely, roots growth of Tetraena mongolice maxin remains unaffected when the surface tensile strain was less than the average ultimate tensile strain of roots. Therefore, goaf backfilling is an effective mining method to protect the Tetraena mongolice maxin.

Stability of numerical simulation and security monitoring of filling method to mining the hanging wall ore on high-steep slope

WU Shan, SONG Wei-dong, DU Jian-hua, ZHANG Xing-cai, ZHOU Jia-xiang

2013, 30(6): 874-879.

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Exploitation of hanging wall ore with filling method can not only recycle ore, but also avoid decline of the slope and control deformation of surrounding rock effectively. Based on the hanging wall ore mining by filling method of Daye Iron Mine, Cavity Monitoring System (CMS) is used in this paper to detect the original goaf of hanging wall ore. Then stress, displacement and plastic deformation of surrounding rock and open-pit slope in the processing of mining the hanging wall ore are analyzed by CMS and 3D mine-FLAC3D coupled method. The calculation results show that the surrounding rock and open-pit slope deformation can be controlled by filling the goaf effectively, so that the hanging wall ore can be mined safely. In the process of mining the hanging wall ore, monitoring network containing stress, fractures convergence and total station is established to monitor real-timely the displacement and stress changes of the surrounding rock, the pillar and the slope. The monitoring results are generally in agreement with the numerical simulation.

Pipe transportation characteristics of filling slurry in Xinyang mine

DONG Hui-zhen, FENG Guo-rui, GUO Yu-xia, QI Ting-ye, KANG Li-xun, GUO Xiao-yan, HAN Yu-lin

2013, 30(6): 880-885.

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Goaf filling is the current efficient solution to solve mining subsidence and surface damage during coal mining. The filling material which is prepared with fly ash and coal gangue is pumped into the goaf through the pipe, which not only can provide the material source for filling, but also control the environmental pollution caused by coal gangue and fly ash disordered stacking from headstream. The pipeline transportation is one of the important links. As one of the key points in the design of a pipeline transport, the flow resistance of pipeline is related closely with the pressure loss and flow. There are important parameters in transportation system design, and directly affect the selection of power equipment and the cost of operation. In view of the uncertain status of flow law for the pipeline transportation of high concentration cemented filling slurry, a pipeline transportation test was con- ducted, and the pipeline transportation features with the filling slurry concentrations of 80% and 81% was studied. The results show that the pressure loss shows cyclic change with the change of time during the pipe pumping process, and the pressure loss increases as the concentration, velocity and frequency increase, Meanwhile, the pressure loss shows a linear growth correlation with the velocity of slurry.Morewove, the flow rate also shows a linear correlation with the slurry velocity, which increases with the velocity increases.

Study on roof stability of open backfilling based on elastic plate model

GU Wei, ZHANG Li-ya, TAN Zhi-xiang, DENG Ka-zhong

2013, 30(6): 886-891.

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The key of using super high water material open backfilling technology is to maintain the integrity of the roof. The filling face can be simplified into five kinds of boundary support elastic plate. They are: four edges clamped board, three edges clamped side of the simply supported plate, two sides clamped on both sides of the simply supported plate, one side clamped and trilateral simply-supported plate and plate with four simply supported edges. Furthermore, based on the principle of virtual work, the elastic foundation plate and the expression of elastic plate deflection and bending moment when four edges are affected by the horizontal pressure effect are deduced, and the relationship between plate maximum bending moment and forward distance are analyzed. Thus, the model provides the theoretical evidences for the mining width of super high water material open backfilling mining working face and the layout mode of working face. According to the analysis of field measured data, the correctness and reliability of the model can be verified.

Study on the characteristics of variable mass seepage and water inrush mechanism of collapse column

ZHANG Kai, YAO Bang-hua, WU Song-gang, ZHANG Hong-tu

2013, 30(6): 892-896.

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Based on the seepage theory of porous media, the mass conservation equation, momentum conservation equation and the porosity evolution of particles in collapse column with fluid-structure interaction is deduced and a mechanical model for collapse column water inrush is proposed, which takes the mass variation during the seepage into consideration. Then, numerical simulation is carried on using COMSOL Multiphysics, which is a Finite Element Code. By assuming that the porosity in collapse columns obeys the Weibull distribution, the distribution of the porosity and seepage velocity in the collapse column at different times is obtained, and the seepage discharge is calculated. The results show that: 1) the seepage channels initially distribute randomly, however, with the different erosion effect of water on rock with different porosity, they finally form several main channels; 2) the seepage capacity of the collapse column initially grows slowly, while seepage velocity increases significantly with the growth and connectivity of porosity.

Experimental study on drilling feedback signal characteristics of mudstone seam in coal measures

LIU Hong-tao, ZHAO Zhi-qiang, WANG Zhi-gang, ZHAO Xi-dong, WANG Guang-hui

2013, 30(6): 897-902.

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Taking the mudstone in the coal measure strata as the research object, this thesis carries out a field test on the drilling feedback signal under different thrust level in drilling process of different compressive strength mudstone seam. The results show that：1) In test conditions, the thrust-rotational speed characteristic curves of drilling mudstone process can be obviously divided into three areas-grinding area, drilling area and blocking area. The grinding area will jump into the drilling area when the thrust reaches a certain value, but the transition zone is not obvious. 2) Drilling rate approximate increases linearly with the thrust in drilling area, which minimizes power consumption and is the optimal region for drilling rig’s working; 3) In blocking area , drilling’s growth rate does not decrease but grow negatively. The drilling rate decreases with the increasing thrust and the drilling rate dips to zero when the thrust reaches a certain level; 4) Under the same thrust, the drilling speed and the mudstone strength show an exponential relationship. With the increase of the mudstone strength, the characteristic curve of the drilling speed and the mudstone strength features show that both the drilling area and the obstructed area shift to right, the area of the thrust increases, the peak value of curve decreases and the position of the peak shifts to right and becomes flat.

Elastoplastic solution for surrounding rock of circular roadway based on D-P criterion by considering post-peak strain softening and dilatancy

ZHANG Xiao-bo, ZHAO Guang-ming, MENG Xiang-rui

2013, 30(6): 903-910.

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In this paper, the circular roadway surrounding rock was divided into plastic residual zone, plastic softening zone and elastic zone, and the softening modulus of strength parameters, coefficients of dilatancy and shear dilatancy angle were introduced by considering the rock post-peak strain softening and dilatancy. Meanwhile, based on Drucker-Prager criterion and its generalized non-associated flow rule, the relationship between dilatancy angle and softening zone coefficient of dilatancy was estab- lished. By using Lode parameter to describe intermediate principal stress, the analytical solutions of elastoplastic stress, displacement and plastic zone radius were obtained. In addition, an example was analyzed to study the effect of different factors on plastic zone radius and displacement of surrounding rock. The results show that the intermediate principal stress has significant effect on plastic zone radius and displacement, and presents the interval characteristic. The larger the residual value cohesive force and internal friction angle are, the smaller the plastic zone radius and displacement are. Meanwhile, the selection of dilatancy angle has great influence for analysising dilatancy, and softening modulus decreasing and supporting resistance increasing can control the surrounding rock deformation in different drgree, while softening mainly has effect on plastic residual zone radius and dilatancy mainly has affect on displacement of surrounding rock.The study in this paper can provide theoretical basis for surrounding rock stability evaluation and supporting quantitative design.

Research on the risk evaluation methods of water inrush from coal floor based on dimensionless multi-source information fusion technique

ZHU Zong-kui, XU Zhi-min, SUN Ya-jun, HUANG Xin-lei

2013, 30(6): 911-916.

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Effective evaluation of the risk of water inrush from coal floor is the prerequisite and basis for coal mine water hazard control and safety mining. The paper researches the risk evaluation methods of water inrush from coal floor based on dimensionless multi-source information fusion technique. Taking Xin’an coal mine as example and based on systematic analysis of floor water inrush mechanism, six key factors affecting the water inrush from the floor of NO.21 coal seam including distribution of faults belts, distribution of the endpoints and intersection-points in faults, index of water inrush caused by faults, water pressure and watery of the Ordovician limestone aquifer and the effective aquifuge thickness are identified and dealt with dimensionless quantity due to the structural and hydro-geological conditions. The weights of each factor are determined by qualitative arrangement and quantitative transformation. After that, dimensionless multi-source information fusion model for the evaluation of the water inrush risk of NO.21 coal seam in Xin’an coal mine are established on the basis of the GIS multi-source information fusion technique. The result is proved to be reliable when the model is applied into the evaluation and prediction work of water inrush from coal floor in this coal mine.

Drainage radius measurement based on gas flow field

JI Huai-jun, LI Zeng-hua, YANG Yong-liang, LIU Zhen, YANG Ji-chao

2013, 30(6): 917-921.

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In this paper, to accurately determine the drainage radius, and reasonably estimate the drainage parameters of different regions in the same mine, the mathematical model of gas pressure in coalmass around borehole was established by the gas flow theories, the calculation program of drainage radius was designed by using VB.NET, and the distribution rules of gas pressure around borehole and the influence factors were simulated. Meanwhile, drainage radius was measured with the method of pressure-drop testing by circumference setting-borehole. The results show that the draining time, permeabilities and subpressure are the main factors which influencing the distribution rules of gas pressure. The actual measured drainage radius of No.8 Coal Seam in Luling Mine is 4.32 m, while the calculation results is 4.43 m, which means the proportional coefficient method can calculate the drainage radius of other zones in the mine reasonably. The achievements in this paper can provide basis for gas drainage borehole design, raise gas drainage efficiency, and ensure safety mining.

Multi-index comprehensive identification and real-time warning of coal and gas outburst

GUAN Wei-juan, ZHANG Guo-shu, ZHAO Zhi-gen, CHEN Qing-hua, CHEN Ming-qiang, XU Guang-quan

2013, 30(6): 922-929.

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In this paper, to realize the accurate identification and timely warning of coal and gas outburst, a new early warning index system was built, and a real-time warning system was designed. The early warning index system includes real time indexes, dynamic indexes, and fundamental indexes. The real time indexes mainly refer to volatility, frequency, concentration amplification and moving average, which reflectes the phenomenon and essence of gas abnormal effusing, and the dynamic indexes include abnormal drilling, crustal stress display, concentrated stress, geological structure, etc, which mainly reflectes anomaly of gas pressure and crustal stress, while the fundamental index mainly reflectes the anomaly of coal seam geology. Then, based on C/S frame, the real time warning system of coal and gas outburst was designed, through which distributed approach of data, multi-channel expression and grad- ing diffusion of warning information can be achieved. Finally, the early identification and real time warning of outburst were simulated according to the historical outburst data of one mine. The results show that the warning level of outburst can be achieved to response level three hours earlier, which can meet the requirements of identification and warning of coal and gas outburs in coal mine.

Influence of fault strike on gas outburst under modern tectonic stress field

JIA Tian-rang, WANG Wei, ZHANG Zi-min, TAN Zhi-hong, ZHANG Yong-jun

2013, 30(6): 930-934.

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Along with the increasing of mining depth, crustal stress is playing more and more important role in coal and gas outburst By using theoretical analysis, numerical simulation and field investigation, the influence of fault strike on gas outburst under the modern tectonic stress field is discussed in this paper. The results show that the risk of coal and gas outburst is mainly controlled by the tectonic evolution and the relationship between fault strike and maximum principal stress direction in the modern tectonic stress field. When the fault strike is parallel to the maximum principal stress, it contributes to stress re-lief featuring, better gas permeability of coal seam, and small risk of outburst. But at the end of fault, especially at the lower end of fault, stress concentration may occur and gas occurrence conditions are relatively good, it needs to to pay attention to gas accidents.Along with the increase of angle between fault strike and principal stress direction, the scope of extruding shear stress concentration increases, and outburst risk scope increases. When fault strike is vertical to maximum principal stress, the extruding shear stress concentrates in a large scope, the coal seam permeability is low, which contributes to the formation of large gas concentration zone, and the outburst risk is largest.

Strong-weak-strong borehole pressurized sealing technology for horizontal gas drainage borehole in mining seam

ZHANG Chao, LIN Bai-quan, ZHOU Yan, ZHAI Cheng, WU Hai-jin, HAO Zhi-yong

2013, 30(6): 935-939.

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To improve the borehole sealing technique of horizontal gas drainage for low permeability and high gassy single coal seam, the “strong-weak-strong” borehole pressurized sealing technology was developed in this paper, and the technology was practically applied in N1-3 Coal Face of Changcun Coal Mine. The practical results show that the technology has siginificant sealing effect, and the effect is increased by times against those of the common ways under the same conditions, namely, the gas extraction concentration increases from 26%~33% to 61%~64%, and the accumulated extraction time of single-hole with 470 m3 gas decreases form 10 d to 3 d. After its implementation in Changcun Coal Mine, the gas extraction concentration and gas accumulated quantity in tailentry of N1-3 Coal Face have been significantly improved. Thus, this technology has provided a new technical measure for borehole sealing in the condition of high gas contents, and has significant economic and social benefits.

Pressure relief and outburst elimination effect of outburst prevention rock tunnel in rock cross-cut coal uncovering region

LIU Zhen, LI Zeng-hua, YANG Yong-liang, JI Huai-jun, TANG Yi-Bo

2013, 30(6): 940-945.

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In this paper, to resolve the problem of rock cross-cut coal uncovering in the super thick and gently inclined outburst coal seam, a new idea through the pressure relief of roof rock tunnel was proposed for rock cross-cut coal uncovering. Theoretical analysis has identified the energy stored in tectonic coals with high pressure gas, which was formed under high ground stress, is the main driving force of outburst in rock cross-cut coal uncovering. Meanwhile, stress distribution of surrounding rock in roof tunnel of thick coal seam was simulated to study the stress variation of coal mass in uncovering coal face. The results show that the roof tunnel can reduce the original stress, transfer the mining-induced stress, weaken the stress concentration effect of deep coal-rock mass affected by mining operation in uncovering coal process, and reduce the influence scope. The roof tunnel can transfer and bear 15% concentrated stress in rock cross-cut coal uncovering, and the pressure relief width in front of the face can be increased by 2~3 m. Thus, duo to the forwarding of pressure relief frontal surface, together with gas drainage by boreholes through coal seam in roof tunnel, the ground stress, gas pressure and elastic energy of coal mass can be reduced significantly. Moreover, the closer the distance between roof tunnel and coal seam is, the better the pressure relief effect is.

Forecasting model of coalface gas emission based on LMD-SVM method

FAN Bao-long, BAI Chun-hua, LI Jian-ping

2013, 30(6): 946-952.

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In this paper, the method that using LMD (Local Mean Decomposition) to obtain production function components for SVM (Support Vector Machine) modeling was proposed, which was applied to forecast the gas emission volume in coalface. First, the historical data of gas emission volume were resolved by LMD to get the production function components, i.e. PF components. Then, extrapolation forecasting of each PF component was carried out by using SVM function fitting method,respectively. In addition, the forecasting results were reconstructed, and the forecasted theoretical values of gas emission volume were finally obtained. From the case study in one mine, the forecasting accuracy of the method proposed in this paper is higher than conventional SVM methods, and the established forecasting model of coalface gas emission based on this method has better rationality and reliability. Therefore, with the acquisition of production function components and small sample forecasting by SVM, the physical mechanisms and laws in data can be fully exploited, which accords well with the physical mechanism that using data themselves to get their interaction. This method provides a basis for improving the forecasting accuracy of gas emission volume.

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