Journal of Mining and Safety Engineering

Relationship between support and surrounding rock of fully mechanized caving face in thick coal seam of kilometer deep mine based on microseismic monitoring technology

JIANG Fuxing, YIN Yongming, ZHU Quanjie, WEN Jinglin

2014, 31(2): 167-174.

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Based on the high precision microseismic monitoring technology and the rock mechanics and rock pressure theory, overburden strata movement law has been gained at 3107 working face in Shengjian Coal Mine，and the relationship between support and surrounding rock on the fully mechanized top coal caving face in thick coal seam of kilometer deep mine has been studied．The results show that the microseismic events located within the lower strata are of high density distribution，and microseismic events located within the higher strata are of low density distribution．The periodic distribution of microseismic events in both space and time correspond to the periodic movement of roof strata，and the high rock fracture force the lower strata fracture．The relationship between support and strata high rock fracture force the lower strata fracture．The relationship between support and strata with pe- riodic rock fracture of the basic roof can be drawn as follows：1) In the aperiodic weighting period，the basic load of the support originates in the static pressure caused by such forces as the top coal of 4.4 meters thickness，the lower immediate roof of 20 meters thickness and part of the upper immediate roof of 20 meters thickness；2) In the periodic weighting period，the basic load of the support originates in the dynamic pressure caused by the basic roof fracture and the static pressure caused by the weight of the top coal and the immediate roof．The dynamic pressure causes impact load on the support，which is the main reason that hydraulic support is crushed．Some measures such as decrease of top coal recovery rate in advance and increase of support extension should be taken so as to reduce the impact on the hydraulic support．

The influence of stress disturbance on the danger of rock burst

LU Aihong, MAO Xianbiao, PANG Zengwei

2014, 31(2): 175-179.

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The energy accumulation and its position are two main factors on judging the rock burst occurring. An energy density criterion to distinguish the danger of rock burst is put forward based on this assumption in this paper. The process of the energy accumulation and the effect of the intensity of stress wave pmax to the energy accumulation are simulated and analyzed by employing ANSYS/LS-DYNA，and the characteristic and the position of the energy accumulation are obtained. Research results show that：1) With the stress wave increasing the value of the Udmax is increasing. When the intensity of stress wave pmax increasing from 5 MPa to 20 MPa，the incremental value of the energy density is 2.007 MJ/m3 to 3.981 MJ/m3，incremental rate reaching 98%；2) Due to the impact of the distribution intensity pmax，with the stress wave increasing the position of Udmax moves to the inside of the roadway side. When the intensity of stress wave pmax increasing from 5 MPa to 20 MPa，the incremental value of energy density factor k is 1.384 MJ/m4 to 4.976 MJ/m4，incremental rate reaching 259%，which means the notable increase of the possibility of the rock burst.

Experimental research on fault reactivation and relating coal bumps

WANG Tao, JIANG Yaodong, ZHAO Yixin, ZHANG Yunyi

2014, 31(2): 180-186.

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Based on the prototype of No.21221 face of Qianqiu coal mine, a similar simulation experiment with a fault passing through the mining face is designed. The law of the fault stress evolution and induced overlying strata motion is studied by reproducing the physical process of fault reactivation and coal bumps. Meanwhile the mechanism of fault reactivation under the influence of mining is analyzed. It is observed that the normal stress and the shear stress rapidly increase when the moment is close to fault reactivation, and the risk of fault to slip increases at the same time. Under the mining influence, the fault is easy to reactivate until the working face is 25 meters away from fault along the hanging wall. The mining influence raises the possibility of fault reactivation; the important cause leading to the fault slip is the partial failure of the coal bearing capacity. In addition, the influences of fault slip on the coal act as the unsteady-state impact and the loading-unloading effects.

Situation assessment method of rock burst based on multi-source information fusion

JIA Ruisheng, YAN Xianghong, SUN Hongmei, FAN Jiancong, YANG Huibin, WU Chunfang

2014, 31(2): 187-195.

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Rock burst situation assessment is one of the key and difficult issues in the safety monitoring and early warning field of coal mining. In this paper, based on real-time data from microseism, acoustic emission and electromagnetic radiation monitoring, situation assessment theory was introduced to the rock burst prediction, and a new situation assessment model of rock burst was established based on log audit of monitoring system and real-time correction algorithm. In addition, the situation quantitative method of rock burst was put forward by improving D-S evidence theory. Moreover, by using this method to calculate situation values in continual time points, the predictive values of rock burst situation were calculated and analyzed based on GM (1, 1) and ARMA models, respectively. Test results and related analysis show that the proposed situation prediction method of rock burst is reasonable and effective, and can reflect the development trend of rock burst dynamically.

Quadratic optimization of mining microseismic source positioning based on cluster analysis

ZHU Quanjie, JIANG Fuxing, MIAO Huaxiang, WU Yingkui, LIU Xiaohui

2014, 31(2): 196-202.

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In order to improve the precision of the microseismic location, the quadratic optimization of mining microseismic source location has been researched through using MATLAB software and its toolbox in this paper. First, the microseismic location problem is boiled down to solving linear equations using traditional mathematics method and a Four-Four combined positioning model is set based on a multiple sensors; second, the k-means clustering method is applied to optimize the positioning results. Two classes—core cluster and peripheral cluster are set to processing those data. When it meets the principle of heart knee point and noise migration distance, the circular will stop and the final result will be solved. The result of field test shows that the optimized results are in close proximity to the real source; the distance between those is about 12.08 m (x：1.8 m，y：2.83 m，z：11.6 m). This method is simple and easy to operate, and the precision has been improved compared with the single positioning method.

Rock burst risk evaluation based on particle swarm optimization and BP neural network

LI Huimin, LI Zhenlei, HE Rongjun, YAN Yubiao

2014, 31(2): 203-207.

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In order to evaluate rock burst risk degree, a new evaluation method based on the model of particle swarm optimization (PSO) algorithm and BP neural net is proposed. The method employs the technology of BP neural network to establish a regression model and takes advantage of PSO algorithm to optimize the parameters of the network, namely, the weights and the threshold values. All the data used in the model are from existing rock burst database. As a result, the BP neural network cannot fall into local optimum and its convergence speed can be increased. Then, ten major factors are selected as the inputs and twenty practical cases from a characteristic rock burst coal mine are chosen to establish the PSO-BP evaluation model. The newly established model is further compared with the standard BP model. Results show that the evaluation accuracy is increased by 15 percent by the proposed model in this paper. Finally, the proposed PSO-BP evaluation model is finally applied to evaluate the rock burst risk degree of two coalmines, where the feasibility and applicability of the method are verified.

Numerical simulation on top-coal arching mechanism

BAI Qingsheng, TU Shihao, WANG Chen

2014, 31(2): 208-213.

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By analyzing the broken, caving characteristics and motion criterion of top coal and immediate roof behind the shield, the discrete element numerical simulation model for top coal was established in this paper. Meanwhile, from the moving characteristics of coal-rock blocks and evolvement rules of contact force, the top-coal arching mechanism behind shield was discussed. The kinematic mechanism of top coal arching is that there exits a high-speed area of top coal above the coal draw-point, and the moving speeds of coal-rock blocks on the two sides of high-speed area are smaller. The top coal silts at both sides of the coal draw-point, and develops unstable contact force arching above the coal draw-point, which can result in moving speed of top coal near the coal draw-point decreasing. When large-scale top coal blocks in the higher level surge up to the coal draw-point, they can be easily squeezed and form an arch in mining process. The mechanics mechanism of top coal arching is that the drawing process of granular top coal can be seen as a formation and destruction process of the contact force arch. When the upper contact pressure is greater than the frictional resistance formed by the arching extrusion blocks, the contact force arch may damage, otherwise the stable contact force arch appears, and the coal draw-point may be jammed. Field measurements have verified the theoretical analysis.

Study on roof breaking model of near shallow seam

LIU Xuesheng, NING Jianguo, TAN Yunliang

2014, 31(2): 214-219.

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To study roof movement law of near shallow seam, a deep multi-bases displacement monitoring device is adopted to probe roof movement behaviors of 20307 near shallow working face in Gaojialiang Mine. Roof breaking model of near shallow seam is built, and the initial and cycle fracture of key strata are simplified to clamped and trilateral clamped and one-side uniform loaded rectangular plate respectively. The fracture length of key strata is derived using plastic limit analysis theorem and the correction method of fracture length of inferior key strata is put forward. Compared with ground pressure observation, the average error is 7.03%, and the large weightings gain from theoretical calculations and ground pressure observation are almost the same. This research provides a theoretical basis for roof control design of near shallow seam.

Method and application of extending mining upper limit under aquifer by gangue backfill mining

ZHANG Jixiong, LI Meng, DENG Xuejie, LI Jian

2014, 31(2): 220-225.

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Based on the theory of controlling height of mining-induced fracture by gangue backfill mining, the software FLAC3D is used to study the change law of height of water flowing fractured zone. Calculation model of height of water flowing fractured zone between mining height and compaction ratio is gained by the means of multiple linear regression. The determination method of mining upper limit under aquifer is proposed. The results show that the mining upper limit can be extended from -300 m to -255 m and 1.826 million tons coal resources can be recovered on the condition of mining height less than 3.5 m and compaction ratio up to 85%. Through the test of gangue backfill mining in Wugou coal mine, the height of water flowing fractured zone is just 10 m by the leakage volume of drilling fluid. The monitoring results are quite consistent with the theoretical calculation.

Research on the impermeability of upper member of Cambrian and its application on coal mining above aquifer in Malingshan coalmine

ZHU Zongkui, XU Zhimin, SUN Yajun

2014, 31(2): 226-231.

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The structure and thickness of the floor aquifuge are important influencing factors for the safety mining above confined aquifer. Due to Ordovician strata missing in the certain areas of Henan Province, coalmines are often serious threatened by the floor Cambrian limestone Karst water inrush. The hydrogeological structure characteristics in the upper member with the thickness of at least 25 m of Cambrian limestone in Malingshan coalmine is detected in this paper, and then, the water-resisting-isolating capability of the upper Cambrian limestone is assessed. Subsequently, based on the GIS platform, the method of risk assessment for floor water inrush by using the relative impermeability of upper member of Cambrian limestone is studied. By adopting the research result, 13.4 million tons of coal resources in Malingshan coalmine are liberated and 4 million tons of coal resources are safety extracted and then, the shaft station at -350 m elevation is successful tunneled with the depth of 55.5 m and the length of 320 m into the upper member of Cambrian limestone. Owing to considering the existence of the relative aquifuge section locating in the upper member of Cambrian limestone, the result, which more tally with actual situation, has been successful applied in Malingshan coalmine for its coal mining practice above confined water with high pressure.

Analysis of the ground water level change of aquifer-protective mining in longwall coalface for shallow seam

MA Liqiang, SUN Hai, WANG Fei, LI Jiaming, JIN Zhiyuan, ZHANG Wei

2014, 31(2): 232-235.

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In order to solve the contradiction between the protection of water resources and mining, according to the classified research result of aquifer-protective mining (APM) conditions in shallow coal seam during normal mining process of 32202 longwall coalface of Bulianta mine in Shendong mining area, the min-ing height is determined to be below 5.3 m and large power of hydraulic support and large power and high reliability equipment are selected to ensure that advance rate of coalface is greater than 15 m/d after demonstrating APM mechanism and feasibility. After coalface mined, the water level observation of ground well shows that the water level of No.10 observation well located in the middle of the coalface stabilizes gradually after about 25 days and relatively increases 0.66 m compared to the ground while the water level of No.18 observation well near the tail entry stabilizes after about a month and relatively reduces 0.87 m compared to the ground. The Quaternary loosened aquifer is less affected by the variation of water level and the main plant species of the surface can grow normally. The industrial test shows that aquifer-protective mining technology which features fast forwarding in the long wall coalface can be successfully applied in suitable geological conditions. What’s more, the research can provide reference for ecological environment construction and increases coal recovery rate for the shallow seam of mines with our country.

Recognition method of mine water inrush sources based on the principal element analysis and distance discrimination analysis

GONG Fengqiang, LU Jintao

2014, 31(2): 236-242.

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Mine water inrush is one of the greatest natural disasters in the mining production process. Quick and effective identification of mine water inrush source is an important guarantee of safe production in mining engineering. Seven kinds of water chemical composition having been selected as the sample variables in water bursting source recognition，and a forecast model of water inrush source is built by combining distance discriminant analysis with principal component analysis. This model is tested and applied in the different water layer of Xieyi Coal Mine in Huainan with thirty-three training samples and eleven predicting samples，and it is compared with the gray correlation discrimination model and Bayesian discrimination model. The results show that the model shows 95% of accuracy，and the predicting correct rate is up to 91%，which provides a new method for mine water inrush identification.

Simulation on deformation and failure of ground surface and overlying rock caused by extracting inclined ore body near surface

CHEN Luwang, SUN Rui, BAI Shiwei, MAO Haijun, LIU Jinlong

2014, 31(2): 243-248.

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In order to reveal the mechanism of deformation and failure of ground surface and overlying rock caused by the extracting inclined ore body near surface, the paper takes a typical geological section of a copper mine for example. The generalized physical model experiment and UDEC numerical simulation are applied to analyze the change law on deformation and failure of ground surface and overlying rock in different extracting steps. Both the physical model experiment and numerical simulation show that when the ore body is extracted above at -45 m, the local disturbance in the overlying rock will occur with small displacement; when the ore body between -45 m and -75 m is extracted, the displacement will increase and the subsidence area will gradually expand. Consequently, abscission layer appear and the damage spread to surface. If the reserved rock pillars are extracted, the overlying rock will collapse entirely and the abscission layer will become obvious; thus, dislocation and rotation will appear in overlying rock, and the rock failure spread to the ground surface. Rational utilization of generalized physical model experiment, coupled with numerical simulation, will intuitively and accurately simulate the dynamic evolution process on deformation of ground surface and overlying rock.

ZHANG Jun, WANG Jianpeng

2014, 31(2): 249-254.

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The “three zones” height of mining overburden roof strata of fully mechanized working face 68303 in Du’erping coal mine have been studied by similar simulation experimental method based on the overburden rock mass failure properties and the characteristics of fractures distribution and development. The heights of caved zone, fractured zone and continuous deformation zone are 12.5 m, 37.5 m and larger than 80 m respectively by research of gob roof strata fracture, separation and convergence, distribution and extension of fractures. The experimental results are compared to the in-situ measurements of upward inclined holes water injection and the flow parameters. The heights of caved and fractured zone differ by 0.8 m and 2.5 m respectively from the in-situ measurements. The results show that the similar simulation experimental study based on the characteristics of fractures distribution are reasonable and reliable, which can be used as effective means for the research on overburden roof strata “three zones” height of working face.

Determining the reasonable width of narrow pillar of roadway in gob entry driving in the large pillar

ZHANG Kexue, JIANG Yaodong, ZHANG Zhengbin, ZHANG Yongping, PANG Xufeng, ZENG Xiantao

2014, 31(2): 255-262.

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Gob entry driving in the large pillar is a new technology based on double U-shaped roadway layout of the face. According to the geological conditions, certain method of reasonable width of narrow pillar in gob entry driving in the large pillar is obtained based on the combination of limit equilibrium theory, numerical calculation and field practice. It takes into account six parameters for the narrow pillar width from distribution of stress of the section of the lateral support goaf, stress distribution of coal pillars, stress distribution of surrounding rock, plastic zone distribution of surrounding rock, the relationship between deformation of surrounding rock and pillar width and limit equilibrium theory of narrow pillar width, and finally it is determined that the narrow pillar width is five meters. Then deep analysis is conducted to the impact of stress distribution law between narrow pillar and wide pillar to this section face mining.

Instability mechanism and control technology of chamber group surrounding rock in complex structural area

WANG Qizhou, XIE Wenbing, JING Shengguo, FEI Xiaobao

2014, 31(2): 263-269.

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In this paper, to obtain the stability characteristic and control countermeasure of chamber group surrounding rock in complex structural area, taking the chamber group in pump room of No.42 mining district in Peigou Coal Mine as example, the loosen zones of chamber group surrounding rock were detected by geological radar and drilling peep instruments. Additionally, FLAC was used to analyze the influence of horizontal tectonic stress on plastic zone layout of roadway surrounding rock, as well as the influence of chamber group structural characteristic on its own surrounding rock stability. Based on these, the cooperating support of frame and anchor cable, and the bolt-mesh-anchor supporting technology for roadway floor were put forward according to the lithological characteristics of chamber group. The industrial results show that chamber group can be effectively maintained after adopting the rational support scheme.

Determining the optimum position of roadways of full-mechanized caving face in the close distance seams

KONG Dezhong, WANG Zhaohui, REN Zhicheng

2014, 31(2): 270-276.

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To solve the problems in determining the reasonable position of roadways in the close distance seams，the depth of destroyed floor，the stress distribution in the floor under a coal pillar left in the upper coal，and the reason why roadways are easy to transform and fail under heterogeneous load are studied through numerical simulation and theoretical calculation. The result shows that the maximum depth in the floor caused by the abutment pressure from the upper coal being mined is 25.3 m，which spread to the level of roadway in the close distance seam. The stress distribution in the floor around the pillar has obvious heterogeneous characteristic：the stress-concentrated area lies under coal pillar and concentration degree decreases quickly away from the center of coal pillar. The roadway support structure is subject to overlarge partial tension stress and produces deformation and failure under the heterogeneous load. The change of principal stress is defined to evaluate the heterogeneous degree. Considering that the resource is recycled to the maximum, combined with the stress distribution characteristics of the numerical simulation, an inner stagger distance of 14 m for the roadways in the close distance seams is determined.

Construction and safety monitoring analysis of 3D visualization system for Da’anshan coal mine

LI Yang, YANG Tianhong, LIU Honglei, ZHANG Penghai, WANG Xinrong, YIN Dafa

2014, 31(2): 277-283.

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In order to achieve the organic connection between field monitoring data and mining temporal-spatial correlation, to make the whole predictive analysis and monitor, and to evaluate surrounding rock stability and safely mining, a set of 3D visualization mining system combined with the actual conditions of Da’anshan coal mine has been developed. The mining system is based on Northeastern University virtual reality system software, which not only includes three-dimensional scenes, but also realizes the functions of virtual roaming, database information inquiry and interactive control. By the secondary development of virtual reality software, its ability of integrating 3D data is strengthened. Through comprehensive analysis of the data, main roof weighting length, advanced support pressure and failure mode and mechanism of roof weighting are obtained, which provides the scientific basis for roof controlling and safe mining.

Nonlinear creep constitutive model of rock under high confining pressure and high water pressure

JIANG Haifei, LIU Dongyan, ZHAO Baoyun, LI Dongsheng

2014, 31(2): 284-291.

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According to the triaxial creep curves of sandstone under high confining pressure and high pore water pressure, the creep rule of rock is discussed. The Burgers model is selected to describe the characteristics of creep in the low stress level, which can get nice result. When stress exceeds the yield level, the accelerated creep damage of rock will occur after a period of time. The accelerated creep curves are fitted by the mixed equation of power function and logarithmic function. Then, the method of analogy is used to propose a new nonlinear viscous component, which is in parallel connection with the plastic component to constitute a new nonlinear viscoplastic model. By connecting this model with Burgers model in series, a new six-component nonlinear viscoelastoplastic creep model is acquired. Consequently, the creep constitutive equation in three-dimensional state is deduced. With the test result, the algorithm of Universal Global Optimization is adopted to identify the model parameters, which shows that the proposed six-component nonlinear viscoelastoplastic creep model is available and reasonable.

Failure characteristics of prestress fractured rock under uniaxial cyclic loading and seepage water pressure

ZHOU Zhihua, CAO Ping, YE Zhouyuan, ZHAO Yanlin, WAN Wen

2014, 31(2): 292-298.

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In this paper, to reveal the mechanical response of deep rock under the coupled action of ground stress and seepage water pressure when facing dynamic disturbance such as blasting, the seepage pressure loading device was developed, and the uniaxial cyclic loading tests of prestress fractured concrete samples, coupling with and without seepage water pressure, were carried out respectively. The results show that the limited uniaxial cyclic loading is helpful to the strengthening of concrete material when it is in the elastic stage. Under the action of seepage water pressure, the rock strength is reduced after the uniaxial cyclic loading, while the reduction degree is related to the prestress of cyclic loading. Meanwhile, when the cyclic loading is compressed in the elastic stage, the rock strength is higher than that when cyclic loading is compressed in the damage stage. In addition, the rock strain under the action of seepage water pressure is greater than that without seepage water pressure. Therefore, the burst proneness of rock mass can be reduced by the action of cyclic loading and unloading, and the low seepage water pressure can further decrease the rock burst proneness.

Study on the strength characteristics and deformation rule of red sandstone in Meilinmiao mine under negative temperature

DAN Renliang, SONG Liwei, LI Dongyang, LIU Nian, LIU Yan, XIA Yu

2014, 31(2): 299-303.

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The study of mechanical properties and deformation rule of Meilinmiao red sandstone have been conducted on freezing triaxial test machine. Four different confining pressures are applied separately on the samples at -15 ℃, and the effect of confining pressure to rock strength and Young’s modulus are analyzed. The results show that both axial compressive strength and Young’s modulus increase linearly as the confining pressure increases, and the red sandstone still meet Coulomb criterion. Through regression analysis, the cohesion of red sandstone is 12.7 MPa, and the internal friction angle is 30.4°. The rock failure form is related to confining pressure.

Optimization of mix-proportion and diffusing rule of super-fine cement grouting slurry

WU Aixiang, YU Shaofeng, HAN Bin, WANG Yiming, HUANG Mingqing, WANG Yong

2014, 31(2): 304-309.

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The joint fissure of some copper mine is developed, and its surrounding rock and ore body are broken, which needs a great amount of reinforcement. The superfine cement grouting technology is selected, and then according to different ratio of water-cement (W/C) and volume ratio of cement slurry/sodium silicate (C/S), indoor mix optimization test and theoretical research is launched by using orthogonal designing test. Such parameters as the best W/C and C/S were put forward to meet the required strength of grouting pressure, and according to the recommended mix-proportion, test is conducted on the spot. Grouting pressure and diffusion radius are confirmed and in view of the above, the grouting system is built. Industrial application shows that into-hole rate is increased by 25%, with exposed area of the stope roof increased by 110 m2, the stope ore retention volume reduced by about 10%, and ore recovery ratio increased by 23.3% according to recommended grouting material proportion and grouting system. Goals of reinforcing ore body, improving blast holes rate and increasing ore recovery ratio are realized.

Vibration and impact analysis of buffer device of vertical material feeding system in solid backfilling coal mining

LIU Zhan, ZHANG Jixiong, JU Feng

2014, 31(2): 310-314.

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Stability of the buffer device ensures the continuous solid materials feeding progress in backfilling coal mining. This paper models the buffer device according to a typical design with FEM software ABAQUS, then carries out modal analysis and frequency-response analysis under vertical excitation, and analyzes the impact response under simulated working conditions in which the material particles are represented by rigid balls. The buffer device’s resonance area under vertical excitation is near the first natural frequency 4.8 Hz, and this indicates fluctuations of flow rate should be avoided during the feeding progress. The response under simulated working condition shows that the buffer device can bear the impact load under feeding flow at a rate of 700 t/h, and the critical spots are the joints of the key parts.

Parameters of gas tube extraction technology in the upper corner of working face

WU Bing, LEI Baiwei, HUA Mingguo, GUAN Haihe, ZHAO Zhiyan

2014, 31(2): 315-321.

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In view of the bad extraction effect for discontinuous space position of extraction point, serious waste of pipe and high extraction cost in the traditional buried tube gas extraction technology in upper corner of working face, the gas tube extraction technology in the upper corner was introduced in this paper, which can make the extraction point matching the face advancing speed, realize the continuity of the best goaf gas extraction effect, recover pipes and materials, and reduce the extraction cost. The selection of optimal location of goaf gas extraction, namely the determination of extraction parameters, is the successful implementation of gas tube extraction of the upper corner. The behavior of gas diffusion and flow were described by using Brinkman equation, Fick diffusion law and gas diffusion translation equation, and the multi-physical field coupling model of gas flow in working face was established. Then, the optimal layout parameters of the tube extraction were determined by Fluent calculation of the model, and was applied to the practice and effect test. The results show that the numerical simulations are basically in accordance with the field test results, and the optimum extraction position has been determined as 2.4 m from the floor, 1.57 m from the air-return roadway along the inclined direction, and 17.4 m deep into the goaf along the strike. Gas overrun in the upper corner has been eliminated during the application, which proves that the gas tube extraction technology in the upper corner has a good applicability and feasibility.

Influencing factors on permeability of loaded gas-bearing coal mass

WEI Jianping, LI Bo, WANG Kai, WANG Dengke

2014, 31(2): 322-327.

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To investigate the influencing factors of the permeability of loaded coal mass containing gas, with the self-developed thermo-fluid-solid-stress coupling equipment for gas-bearing coal mass, the gas permeability characteristics of coal mass in the conditions of different effective pressure, pore pressure and temperature were analyzed in this paper. In addition, by considering the amount of adsorption deformation, the pore gas compression amount, and the variable quantity of temperature expansion, the qualitative and quantitative relationships between the permeability of loaded coal mass and the effective stress, pore pressure, temperature were established, respectively. The results show that when the temperature is under a certain value, the permeability presents negative exponentially proportional to the confining pressure. When the confining pressure and axial compression are fixed, the permeability and pore pressure of coal sample appear V-shape relationship while considering the Klinkenberg effect. According to experimental results, the critical value of pore pressure while Klinkenberg effect occuring were obtained when the confining pressure are 2.0 MPa and 3.0 MPa respectively. Meanwhile, the relationship between the temperature and permeability isn’t the monofonic function under different effective stress, but exists a turning point in the curve. Permeability increases with the increase of temperature and presents outward expansion in the low stress areas, while it decreases with the increase of temperature and presents inward expansion in the high stress areas. Finally, the permeability calculation formula under the combined impact of pressure and temperature was proposed.

Key technology for gas content direct determination method in underground mine

ZHANG Shutong

2014, 31(2): 328-332.

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In view of coal seam condition, coal samples were divided into four categories according to there particle sizes. Based on the theoretical research on gas desorption speeds of coal samples with different sizes, the sampling conditions, sampling methods and sampling times of coal samples with different sizes were analyzed systematically according to the gas desorption data from field and laboratory measurement. Meanwhile, according to applicable conditions of mature sampling equipment and methods, such as coal barrel, pressure air ejector coal sampling equipment, reverse circulation plus wind pressure coal sampling equipment, and orifice connected with coal powder method, the suitable sampling technology and methods of coal samples with different sizes and sampling conditions were put forward, which can provide instruction for gas content direct determination in underground mine.

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