Journal of Mining and Safety Engineering

Mechanism of rock deformation and failure and its control technology of roadway driving along next goaf in fully mechanized top coal caving face of deep mines

WANG Dechao, WANG Qi, LI Shucai, WANG Fuqi, RUAN Guoqiang, SHAO Xing, LIU Wenjiang, WANG Xin

2014, 31(5): 665-673.

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According to field investigation and deformation monitoring of roadway driving along goaf in fully mechanized top coal caving face in Zhaolou mine, failure characteristics of roadway surrounding rock have been analyzed and its deformation failure mechanism has been deeply revealed. Results indicates that low surrounding rock density, high in-situ stress, large destruction scope, unreasonable supporting structure and parameters, complex stress environment and large section size are the main reasons of surrounding rock failure and deformation. Based on control principle of intensive-yielding- coupling support and key parts reinforced support, supporting measures of roof bolt net strip cable, longitudinal strip + two sides anchor net ladder cable, longitudinal steel ladder + narrow coal pillar cable reinforcement and gunite + entity coal side drilling to relief stress are proposed. In addition, field test has been implemented. After roadway driving along next goaf stability, the effect of roadway surrounding rock is good. The maximum force of bolts and anchors are within their yield range, and set aside a sufficient margin for the recovery period. The results can provide a reference for similar complex and difficult supporting roadway.

Deformation failure mechanism and control technology of mining-induced roadway near a fault

WANG Xiangyu, BAI Jianbiao, LI Lei, HAN Zhiting

2014, 31(5): 674-680.

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In response to the surrounding rock asymmetric deformation failure and supporting structure failure during excavation of Hongling Coalmine mining-induced roadway (15141 upper roadway) near a fault, numerical simulation and engineering application of its deformation failure mechanism and control technology have been studied. The results show that asymmetric mining-induced stress field near the fault zone, shearing slippage damage among the key parts of roadway and hulking deformation of coal and rock mass are the main causes of the asymmetric large deformation failure and supporting structure failure. The surrounding rock control technology of this kind of roadway, with reinforced support of key parts by using high-resistance yielding support and grouting reinforcement to control shearing slippage damage of key parts and improve its carrying capacity, weaken differences in deformation of key parts of surrounding rock and prompt uniform bearing on supporting structure, has been put forward to control asymmetric large deformation of the roadway by using asymmetric coupling support principle and high-resistance yielding bolt mechanical property. The research results have been successfully applied to a field trial, which means by using high-resistance yielding support and routing re- inforcement asymmetric support technology, deformation and asymmetry of the roadway can be controlled effectively and stability of surrounding rock can be improved substantially.

Simulation study on key influencing factors to the roof abscission of the roadway with extra-thick coal seam

YAN Hong, ZHANG Jixiong, WANG Sigui, CAO Yuanwei

2014, 31(5): 681-686.

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The roof abscission of the coal seam and rock strata is the omen to the final loosing stability of the roadway with extra-thick coal seam (RETCS) during the excavation and mining activities. It is a basic research on the key influencing factors of the roof abscission as this study can effectively control the value and regeneration of the roof abscission and decrease the roof abscission occurrence ratio, which can prevent the roof caving accidents. Combined with field observation, numerical simulation, orthogonal test and theoretical analysis methods, the influencing factors of the roof abscission of the RETCS are classified and the simulation methods of the roof abscission and key influencing factors of the roof abscission of the RETCS are analyzed in detail. Finally, the main results are as follows：1) The influencing factors of the roof abscission are classified into 3 broad categories including supporting parameters, coal seam and parting properties and roadway structural arrangement and 15 concrete types. 2) The simulation and calculation methods between finite element and discrete element are compared and the latter software with block inlay type are determined and chosen. 3) Based on UDEC and orthogonal test, a total of 50 numerical models according to the 15 influencing factors of the roof abscission are built and simulated and 3 categories of influencing sequence chart and 6 key influencing factors are obtained.

Fracture principle and surrounding rock control of super-high roadway in thick coal seam

XU Lei, HE Fulian, WANG Jun, WANG Yanfei, LI Bo, WEI Haixia

2014, 31(5): 687-694.

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In response to the surrounding rock control problem of ultrahigh roadway, the ultrahigh segment of No.5205 belt transportation roadway in a mine has been selected as research object, the distribution characteristics, development law and relative evolution tendency of fracture field have been researched by UDEC numerical simulation within the height from 3.5 m to 8 m. Results show that surrounding rock fracture field has three areas: fracture transfixion area, fracture development area and microfracture area are all distributed as semi-ellipse. With the height increasing, three fracture areas depth of roof, floor and two sides increases gradually. The transformation from the microfracture area to the fracture development area and from the fracture development area to the fracture transfixion area is strengthened in roof and floor. On the contrary, the transformation from the microfracture area to the fracture development area and from fracture development area to the fracture transfixion area is reduced gradually in the two sides. Equal-stress axial ratio with different height when side-pressure coefficient equals 1.0 is analyzed. The results show that floor void reinforced area height decreases as negative exponent and two sides void reinforced area thickness increases as positive exponent with the height increasing. It is believed that bolt can control fracture slip and delay surrounding rock bulking deformation; side diagonal cable and beam can be anchored to the no fracture region in the shoulder and floor. It has stable and reliable anchor foundation and can squeeze the fracture transfixion area in middle part of the side. Based on this, the combined support technology of high strength and high pre-stressing bolt net bar & diagonal cable and beam is proposed. Super-high roadway will reach self-stabilization after it was dig out after 10 days. Roof-to-floor relative convergence is 104 mm, with two sides relative convergence 150 mm and total roof separation 3.5 mm.

Simulation analysis of influence of floor weak interlayer on floor heave in deep mining roadway

SUN Lihui, JI Hongguang, YANG Bensheng, ZHANG Lei

2014, 31(5): 695-701.

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In order to analyze the influence of floor weak interlayer on floor heave in roadway surrounding, eight models based on different position and number of weak interlayer in the floor have been constructed by combining numerical simulation with theoretical calculations. The influence of interlayer on floor heave deformation, plastic area and stress distribution law has been analyzed. The simulation results show that: 1) The volume of roadway floor heave increases gradually with the increase of interlayer number, and when there are 3 interlayers in the coal floor, the volume of roadway floor heave is 1.88 times than the volume without interlayer, while when there are the same number of interlayer, shallow part and deep interlayer have greater influence on the floor heave in deep level than middle-deep interlayer. 2) The strength of floor surrounding rock is weakened by partial shallow interlayer, which causes the increase in the tensile failure depth of floor. Unbalance energy is absorbed by middle- deep and deep interlayer, so that the original rocks area form in the vicinity of the level of surrounding rock. Deep interlayer can decrease plastic area compared with shallow part interlayer. 3) The stress concentration zone decreases gradually in floor surrounding rock with increase of interlayer number and distance between interlayer and surface of roadway floor. 4) Stress uniform distribution is separated by interlayer, and stress concentration near deep interlayer, in a manner, are formed. According to the simulation results, it is concluded that the roadway with weak interlayer in the floor must be reinforced in order to control floor heave.

Research on the law of instability and caving for large-span cut-hole roof with thin bedrock in depth

JIA Housheng, MA Nianjie, ZHAO Xidong, ZHANG Shengkai

2014, 31(5): 702-708.

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In order to obtain the law of instability and caving for large-span cut-hole roof with thin bedrock in depth during mining, the cut-hole of 1105 great mining height face in Zhaogu No. 2 Coal Mine has been taken for research background. Separate type displacement monitoring instrument of deep roof and separate type bolt (cable) condition monitoring instrument, whose sensors were arranged in goaf and secondary instruments were moved outside, have been adopted for the first time to real-timely monitor the deformation and failure laws of cut-hole roof and dynamic changes of bolt (cable) supporting force during mining. The mechanical model of breakdown destabilization of large-span cut-hole roof has been constructed and the mechanical mechanism of instability and the mechanism of caving of roof has been expounded. The results indicate that the instability and caving form of cut-hole roof is manifested as instantaneous fractures of high-horizon roof in twice. Instability and caving horizon of roof is over 6 m. After the completion of the first fracture, the roof will form hinge structures with certain self-stability. With continues propulsion of coal face, the secondary fracture occurs and then the roof completely collapses. The deformation rate can reach 5.3-19.4 mm/min during the first roof fracture. Accompanied by anchorage invalidation of the bolt, deformation rate is relatively small during the secondary fracture, which is about 2.6-7.2 mm/min.

Simulation analysis on creep failure of deep bolting roadways considering the effect of damage

ZHAO Tongbin, ZHANG Yubao, TAN Yunliang, LIU Shanshan, YIN Yanchun

2014, 31(5): 709-715.

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From creep experiments of deep mudstones in digital speckle method, the phenomenon of deformation concentration that occurs in the surface of specimen is obvious under the first step loading. And it indicates that the damage begin to appear in rock mass under the relatively low stress level. With the increasing of loading level, a shear fracture band is formed until the whole specimen failure. Then the BKS model which can reflect rock damage effect is put forward by introducing damage variable Dt. By using FISH function, the model’s program composition is realized in the FLAC3D. Finally, the model is applied to simulating the bolting surrounding rock control in Kouzidong mining area. The result shows that creep failure zone increases and occurs beyond the anchorage range due to the damage characteristics, and non-continuity failure is obvious during deep surrounding rock. Meanwhile, it is confirmed that the numerical simulation considering damage effect can objectively reflect the creep failure characteristics of deep rock mass by contrasting simulated results with detection results of field borehole. Consequently, there is a guiding significance for the research on failure mechanism of deep roadways.

Overlying strata ellipsoid-style structure of horizontal section top-coal caving in steeply inclined and extra thick coal seam

LAI Xingping, SUN Huan, SHAN Pengfei, QIU Huafu

2014, 31(5): 716-720.

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It is crucial to predict the structure stability of overlying strata in steeply inclined and extra thick coal seams applying horizontal section top-coal caving (HSTCC) method. In this paper, aimed at safe miming in steeply inclined and extra thick coal seams of Urumqi mine region, the formative process and dynamical evolutionary regularity of ellipsoid-style structure of overlying strata in HSTCC condition were studied by using theoretical analysis, numerical computation and field monitoring. The results show that the non-symmetrical trend of vertical deformation is remarkable at HSTCC working face of steeply inclined and extra thick coal seam. Meanwhile, the non-symmetrical arch can be formed due to the composition of top-coal and residual overlying gangue. Sequentially the unique and steep ellipsoid-style structure will be formed dramatically. Finally, the coal-rock mass in the arch angle and apex is slided, and causes the distortion of local rock pressure, even induces dynamic hazards around working face. The results can provide guidance for the design of strata structure and height, and the prevention of dynamic hazard in steeply inclined and extra thick coal seams.

Combination hydraulic support stability of working face in large inclined and “three-soft” thick seam

WU Fengfeng, LIU Changyou, LI Jianwei

2014, 31(5): 721-725.

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In view of the mining conditions of large inclined and “three-soft” thick seam in No.72 Coal Seam of Liudong Coal Mine, the stability and suitability of combination hydraulic support in the high inclined and “three-soft” thick coal seam were studied by using theoretical analysis and field measurement. The results show that the combination support stability is affected by the supporting quality factors including column setting load, uneven coefficient of setting load and prop-setting angle, etc, and the geological factors including dip angle of coal seam, and roof and floor characteristics, etc. The support stability is enhanced with the increase of column setting load, but reduced as the seam inclination increases. Thus, appropriate increasing of setting load in the under side column of combination support will help to improve the support stability, while the reasonable prop-setting angle is one of the important guarantees to improve the support stability in the large inclined seam conditions. In the seam conditions of Liudong Coal Mine, prop-setting angle should be around 6°, and the largest adaptation dip angle of the support is 36.48° Measures have been carried out to ensure the stability of support system in field applications, such as improving the sealing performance of hydraulic system to prevent leakage, enhancing column setting load, and maintaining good-bit states of support and columns.

Thin plate analysis of hard thick strata failure mechanism and its control technology

QIN Guangpeng, JIANG Jinquan, ZHANG Peipeng, SUN Zhongyong

2014, 31(5): 726-732.

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In view of the conditions of double hard-thick sandstone strata without immediate roof above coal seam in Working Face 1007 of one mine, an elastic thin plate model with two adjacent clamper edges, one simply supported edge, and one free edge was established as the mechanical model of hard thick strata. Stress distribution within the thin plate was then studied, and fracture step calculation formula of hard thick strata was obtained. The results show that the maximum point of tensile stress is located at (x=0，y=13b/10π) of the inclination clamper edge and the intersection of strike direction clamper edge and free edge where (x=a，y=b), while the actual position of maximum stress is affected by strata spanning modulus k. The pre-split weaken technology was carried out for the double hard-thick sandstone strata, that is, the lower hard thick stratum was weakened by fan-shaped rotation deep pre-split holes, and the upper hard thick stratum was weakened by ultramultiple-hole longhole blasting, which makes the movement step of the upper hard thick stratum decrease 25.7%, and the lower hard thick stratum changes from main roof to immediate roof. Thus, the accumulated gas ignition risk at the work face corner duo to the suddenly movement of large area hanging strata has been reduced.

Risk evaluation system of abnormal weighting in fully-mechanized sublevel caving face and its application

LIU Jinhai, JIANG Fuxing, GAO Linsheng

2014, 31(5): 733-738.

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Determination of abnormal weighting risk zones is a prerequisite for implementing measures to prevent abnormal weighting. In this paper, on the basis of statistical analysis of factors inducing abnormal weighting in fully-mechanized sublevel caving face, the factors for risk evaluation of abnormal weighting were selected, and risk index was used to characterize risk level of abnormal weighting in coal face. In addition, risk evaluation model of abnormal weighting in fully-mechanized sublevel caving face was established, and the system for abnormal weighting risk evaluation was developed using a modern programming language. An application example was presented in one coal mine of Shandong province; the results agree well with the practice. A new method is provided for risk evaluation of abnormal weighting in fully-mechanized sublevel caving face.

Dynamic forecasting of mining-induced failure depth of floor based on unascertained clustering method

CHENG Aiping, GAO Yongtao, LIANG Xingwang, JI Maowei, WANG Cunwen, GAO Yanhua

2014, 31(5): 739-744.

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According to the microseismic monitoring results, four main influencing factors, that is, mining depth, coal seam dip angle, mining thick and structure impact level, were regarded as judgment indexes and used to establish the dynamic forecasting model of mining-induced failure depth of floor by unascertained clustering method. The mean value of training samples, which come from 18 datasets measured by microseismic monitoring, were set as cluster center, and the weight indexes of judgment were determined by information entropy theory. Through calculating the product sum of multi-index comprehensive measurement of sample and the corresponding sample average, the forecasting value of the mining-induced failure depth of floor was obtained, and then the model was identified by the whole samples. In addition, to further test its reliability, the method was applied to forecast the other five samples to compare the forecasted values with the measured values. The results show that the average of relative error between forecasted values and measured values is less than 1%. The dynamic forecasting model of mining-induced failure depth of floor is reliable and practical, and it can be popularized and applied to the similar mines.

Controlling function of closed compressible support structure on floor burst

XU Xuefeng, DOU Linming, LIU Jun, ZHANG Yinliang

2014, 31(5): 745-749.

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In view of the support technique of coal seam roadway with floor burst hazard, theoretical analysis and numerical simulation methods were used in this paper to study the control function of closed compressible supporting structure made up of anchor net and “O” type shed on floor burst. The results show that high horizontal stress is also distributed in the roadway floor supported with the closed compressible supporting structure, and floor burst risk also exists, compared to the other supporting forms in similar mining geological conditions. Under the dynamic load disturbance, floor burst may happen with the displacement increasing suddenly and the horizontal stress reducing at the same time. However, the roadway does not show obvious floor failure but radial deformation of surrounding rock, and the deformation is relatively small, which shows that the closed compressible supporting structure can’t eliminate rock burst hazard entirely, but can reduce the damage degree. The results can provide reference to roadway support in similar coal mine conditions.

Effect of cementing agents on properties of solid-gas coupling simulation material

LI Shugang, ZHAO Pengxiang, LIN Haifei, PAN Hongyu

2014, 31(5): 750-755.

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Solid-gas coupling simulation experiment in the lab is one of methods of studying on the law of relief methane migration. Development of similar material of coal-rock and gas solid-gas coupling is the basis of the simulation experiment. The cementing material of paraffin and oil have been chosen as affecting factors to carry out the orthogonal test under the condition of changing the content of cementing agents. The influence of paraffin and oil on elastic modulus E and flow rate v of the similar material test-pieces is analyzed. Different proportions of similar material test-pieces have been researched in compressive strength σc, tensile strength σt, elastic modulus E, brittle parameter E/λ and permeability. The equation of permeability has been obtained by combining permeability calculation formula and negative exponential fitting formula of experimental data. It is shown that with increase of paraffin content the permeability present negative exponential. The similar materials can be used in physically simulating experiment, which lays a foundation for the solid-gas coupling physically simulating experiment.

Research on boreholes space optimization of hydraulic flushing considering press relief and gas drainage effect

HAO Fuchang, SUN Lijuan, LIU Mingju

2014, 31(5): 756-763.

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In order to improve outburst elimination of hydraulic flushing, the visco-elastic-plastic model of coal around boreholes considering plastic softening, dilatancy and rheological characteristic has been established, obtaining the parameter of relief ranges of different punching coal amount. At the same time the seepage-stress coupling model considering dynamic change of permeability and adsorption characteristics has been established, and the coupling model has been solved by COMSOL software. Drainage radius of different punching coal amount have been studied, and the boreholes space of hydraulic flushing coal has been optimized. The results show that relief range and drainage radius should be comprehensively analyzed in order to determine boreholes space of hydraulic flushing. When the punching coal amount is 0.5, 1.0 and 1.5 t/m, the relief range is 3.71, 4.61 and 5.8 m, and the drainage radius is 3.5, 4.3 and 5.0 m accordingly. Boreholes space of hydraulic flushing is determined to be 8.0 m because of the average punching coal amount of 1.0 t/m. The data of regional measures effect test and working face prediction show that the boreholes space is reasonable and reliable.

Measurement and numerical analysis of freezing temperature field in Ningzheng coal field cretaceous rock stratum

XI Jiami, LI Qingping, SUN Yonggang, QU Yonglong, LI Borong

2014, 31(5): 764-768.

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Because of very thick water-rich cretaceous strata covered on the seam of Ningzheng coal field, the freezing method is often applied to construct rockshaft. Due to the insufficient research on extension features of the freezing temperature field and the range influence of the frozen wall caused by hydration heat, some problems will exist such as the unreasonable freezing design and the inaccurate time prediction for the closure of freezing wall. Based on the wind well of Xinzhuang mine in Ningzheng coal field, field measurement and numerical simulation have been carried out to study the characteristics of freezing temperature field distribution and influence of outer shaft wall concrete hydration heat. The results show as fellows: temperature falling fast at early freezing, the average rate of freezing can reach to 0.23 ℃/d; the development rate of freeze front reaches to 21.08 mm/d; the affect of concrete hydration heat on the temperature field of the frozen wall by side wall is serious, and the melting depth range of the frozen wall can reach 440-480 mm；the temperature of 3# measuring point from outer wall 50 mm rises 33.6 ℃ with the average heating rate achieving to 2.6 ℃/d. Results by comparing the numerical simulation and field test show that parameter values are basically identical, such as expansion rate of Sandstone freezing wall and well temperature, which can well predict the temperature field variation of frozen wall.

Research and application of TEM detection technology for small mine gob area in shallowly-buried and extremely thick seam

JIANG Zhihai, YANG Guang

2014, 31(5): 769-774.

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Three-dimensional numerical simulation has been carried out to test the theoretical models and high-resistance gob area models in coal mine based on the geophysical model established according to the actual geological conditions of the opencast mine in Hailaer. The response characteristic and distribution law of transient electromagnetic field have been discussed and the parameter of time-depth conversion has been determined. The numerical results show that Transient electromagnetic method can clearly reflect the shallowly-buried and extremely thick high-resistance objective underground. The level curve of the apparent resistivity has a drastic lateral variation, with a camber and concave line, which indicates that it is the high resistivity anomaly area. And numerical method has similar conclusions with physical experiment for the geologic model. For a given geoelectric model when choosing time-depth conversion parameter γ=1.1 or 1.2, the error is small. The applied result shows that: for the inter-mining coal pit, with the buried depth less than 100 meters, as long as a reasonable parameter is chosen, TEM can find out the small mine gob area with over 5 meters in diameter and its distribution range and depth.

Experimental study on retention time of stress memory in schist under uniaxial compression

LIU Yang, LIU Changwu, YU Xianbin, XIE Qiang

2014, 31(5): 775-780.

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In order to study the influence of time on rock stress memory , an experimental study has been performed to investigate the Kaiser effect of acoustic emission on schist at time interval of 2 days, 7 days, 15 days, 30 days and 45 days between the first and second loading under the condition of uniaxial compression, by making use of rock testing machine, as well as a testing apparatus of AE, SDAES. The test results show that with the increase of time interval between two loading cycles, Kaiser effect in rock gradually disappears and the effect is well-pronounced at time interval of 7 days and remains detectable within 30 days, while it is hard to be detected after more than 45 days. The stress level of the first loading affects the fade of Kaiser effect in rock, and rock’s memory ability of precious stress is the best when the stress level of the first loading is of between 30% to 80% of rock strength.

Numerical analysis of lateral pressure coefficient of pores and pore pressure in porous rock aquifer

BO Dongliang, YANG Weihao, HUANG Jiahui, HAN Tao

2014, 31(5): 781-787.

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To provide support for reasonable design of the underground structure lining, random pore models which contain triangle, quadrangle and circular pore shapes respectively have been adopted to study the relationships between horizontal lateral pressure coefficient of porous rock and porosity, pore shape and pore pressure in numerical method. According to whether the contact surface between the rock and the lining has been handled or not, the models are simplified into two kinds, lateral boundary with porosity and without porosity. The main results are as follows：1) Horizontal lateral pressure coefficient decreases linearly with porosity in models without pore pressure, and when porosities are the same, the lateral pressure coefficient decreases with L/A of pores(L means length of the side of pore and A means area). 2) When the pore pressure takes effect on the models, the lateral pressure coefficient increases with pore pressure in both models. The larger the porosity, the more significant change of lateral pressure coefficient will be. 3) When porosity, pore shape and pore pressure of the models are the same. The lateral pressure coefficient is greater in the second kind of model whose lateral boundary contains more pores than the first kind of model. 4) Lateral pressure coefficient increases with L/A of pores when porosity and pore pressure are the same.

Experimental study on b-value characteristics of acoustic emission of cemented filling body under loading and unloading test

GONG Cong, LI Changhong, ZHAO Kui

2014, 31(5): 788-794.

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In order to study the response characteristics of cemented filling body under external disturbance, the studies have been carried out by virtue of uniaxial cyclic loading and unloading tests on cemented filling body, and the -value characteristics of acoustic emission (AE) of cemented filling body is examined. The results show that, during the compression phase, the b-value decreases firstly and then increases. By contrast, the b-value declines orderly as stress increases in elastic stage. After undergoing repeated loading and unloading, the -value reduces greatly as loading stress approaches to the peak stress. Similarly, The AE events are obvious in unloading process. The b-value increases gradually when unloading is started from compressing phase. And when unloading is started from elastic phase, the b-value fluctuates in a small range respectively. Finally, the -value appears step-increasing trend when unloading is started at critical state of cemented filling body. The different -value characteristics indicates that the occurrence of micro crack is in dynamic evolution during loading and unloading process.

Nonlinear SVM with GA in determination of the motion angle of terrane in underground metal mine and its application in engineering

GAO Li, LI Xibing, ZHANG Chuxuan

2014, 31(5): 795-802.

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In order to overcome the shortcomings of traditional methods to determine the parameter of terrane movement in underground metal mines, a new method of the support vector machine (SVM) to predict the motion angle of terrane (MAT) has been proposed. The main factors such as Pu’s coefficient of the hanging wall and foot wall of ore body, geologic conformation, mining depth, mining thickness and deposit angle have been selected as the input variables for the proposed model, and the MAT of hanging wall and foot wall as the output value for the proposed model. On the basis of the different mining conditions and 65 typical metal mines cases, the MAT prediction model of caving method and cut & filling method have been established respectively by using the powerful pattern recognition function of SVM with radial basis function (RBF) kernel. In order to improve the generalization performance and prediction accuracy, genetic algorithm (GA) has been adopted to choose the parameters for SVM model in the current study, thus the MAT with GA-SVM re-gression model for caving method and cut & filling method is established, and Sanshandao gold mine and Sizishan copper mine cases are to be validated for further study of the effectiveness and practicality of the proposed model. The results show that the establishment of SVM regression model prediction of the MAT in underground metal mine can achieve a high accuracy, which provides a new approach to evaluation of the MAT and can be applied to practical engineering, which provides a new approach to evaluation of the MAT.

Numerical analysis of gas migration in enhancement of coal bed methane recovery influenced by thermal field

CHEN Xinzhong, ZHANG Liping

2014, 31(5): 803-808.

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According to the thermoelasticity, convention and dispersion theory and porous medium thermodynamics, the thermal-hydrological-mechanical coupling equations of enhancing coal bed methane have been established in terms of coal deformation, gas migration and heat transport. The numerical solution has been presented in order to investigate the effect of the temperature field on the gas migration in enhancement of coal bed methane. It demonstrates that rising temperature can promote desorption of coal bed methane and quicken coal bed methane production. The results can provide a corresponding theoretical basis for engineering practices of exploiting coal methane, more over it can be referred by the technology of draining gas before extracting coal gassy mining in deep coal seam.

Study on the effect of roof fracture development on gas drainage in steep full-mechanized caving mining

ZHANG Yong, ZHANG Bao, LI Li, ZHANG Shiqing, LIU Jinkai, ZHAO Jianjian

2014, 31(5): 809-813.

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In order to study the roof fracture development and its effect on gas drainage during steep long wall full-mechanized caving mining，combined with relevant theories of elastic-plastic mechanics and fracture mechanics，the mechanics criterion of fracture development in steep coal seam mining has been analyzed，and the gas flow channel has been partitioned as gas isolated channel area, gas transition area and gas network area. Furthermore, the overlying rock fracture development during steep super high coal seam long wall top coal caving mining under the condition of different dip angle of coal seam in Baojishan coal mine has been analyzed，and the changing rules of gas flow channel’s area configuration with the seam angle changing has been obtained．The results of the study shows that the upper part of gas network area are the main areas that the artificial guide channel should run through，and the distribution range of the areas tends to the upper face end and its height increases with the seam angle increasing. The gas drainage plan can be determined according to numerical simulation and theoretical calculation，which will achieve good effect in engineering practice．

Methane burning and explosion mechanism induced by hard roof collapse and its prevention

ZHANG Peipeng, JIANG Jinquan, QIN Guangpeng, WU Quanlin, XU Lina

2014, 31(5): 814-818.

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Taking a fully mechanized top-coal caving face in Xiakuotan Mine as research object, the impact and friction ignition phenomenon caused by hard roof collapse and the mechanism of inducing methane burning and explosion in goaf was studied and by experimental study and theoretical analysis, and the methane distribution law and easy-burning and explosion location in goaf were simulated by using Fluent Software. The results show that the collapse impact and fiction process of hard quartz sandstone roof may produce high temperature spark, which may ignite methane within goaf and induce methane burning and explosion accident. The increased temperature of impact friction surface ΔT is positively correlated, with the mass of collapsed rock m and collapse height H, that is, value in impact friction surface will increase as and H increase. Based on distribution law of goaf methane concentration, the easy-burning and explosion area locates at upper goaf near caving face in the U-type ventilation mode, while the area may mainly distribute in middle goaf in the Y-type ventilation mode. Prevention techniques such as forced roof caving, water and inert gas injection of goaf gangue, and goaf gas drainage, etc, has been put forward.

Evolution law of coal mechanical properties in gas emission process

ZHAO Hongbao, CAO Guangming, LI Huahua

2014, 31(5): 819-823.

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In this paper, taking gas emission process of coal containing different pressure gas in fixed-stress environment as the research object, and taking the axial and transverse strains in gas emission process as study parameters, the coal sample deformation law in gas emission process was studied systematically. The results show that in a certain external stress environment, the evolution law of both the axial strain and transverse strain in gas emission process present obvious nonlinear characteristics. The axial strain of coal sample law presents three-step style, and there exits one point of gas emission speed make the axial strain start to increase in a larger rate, while the relationship between gas emission speed and axial strain can be expressed by improved power function The total transverse strain also shows obvious nonlinear characteristics at the end of experiment. The size of gas pressure has obvious effect on axial strain and transverse strain in process of gas emission,which mainly is manifested in the sensitivity between strain appear point and gas emission speed, and the correlation between total strain, strain formation process, and gas emission speed, etc.

Quantitative research on gas parameter variation

WU Liyun, WANG Fei, YANG Yuzhong

2014, 31(5): 824-830.

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Gas parameters variation has significant influence on the gas disaster prevention in coal mines. In this paper, the initial velocity of gas emission, abutment pressure ahead of the face, gas emission and permeability coefficient in coal seam, et al, were analyzed by the theoretical analysis and numerical simulation. The results show that there are similar or opposite variation regularity among these parameters, which are the combinations of S-shaped curve and inverted S-shaped curve associated to the distance x or time t. Meanwhile, permeability coefficient curve with distance, as well as gas pressure and abutment pressure with distance, all present not exactly symmetrical characteristics. Thus, the variation regularity of parameters can be ascertained with specific coal mine conditions. The research results can provide theoretical guidance to the prevention and control of gas disaster in coal mines.

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