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Nondestructive Testing Principle and Technology of Hydraulic Supports by Ultrasonic Phased Array in Top Coal Caving Face YIN Shuai-Feng, HE Fu-Lian Journal of Mining & Safety Engineering    2012, 29 (3): 328-333.   Abstract （6544）      PDF（pc） （1018KB）（11095）       Knowledge map    Save ased on the necessity of nondestructive testing of hydraulic supports in top coal caving face, the nondestructive testing technology of one-dimensional ultrasonic phased array was proposed in this paper, to accurately inspect the large-scale electromechanical equipment and its components with relatively complex geometric figures. According to the mobile column detection of ZFG10000/23/37H hydraulic supports, the basic principles of phase-controlled focus and phase delay was conducted. Combined with the normalized acoustic pressure function of single element, the significance of sine gain weighted apodization technology was analyzed when applied into reducing the definition of output waveform influenced by sidelobe. Finally, in view of the detection of weld cracking shields at 5201 working face in Wujiagou coalmine, the composition and testing process of nondestructive detection were illuminated. The application examples indicate that the internal micro-fractures and surface interpenetrated fractures of shields can be accurately quantified and located by nondestructive testing technology of one-dimensional ultrasonic phased array, and the development direction and interpenetrated tendency of the fractures can be also exactly judged, according to the results of three-dimensional imaging output. Related Articles | Metrics

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Study on the coupled relationship between AE accumulative ring-down count and damage constitutive model of rock WU Xianzhen, LIU Jianwei, LIU Xiangxin, ZHAO Kui, ZHANG Yanbo Journal of Mining & Safety Engineering    2015, 32 (1): 28-34.   Abstract （4968）      PDF（pc） （489KB）（6640）       Knowledge map    Save In order to study the relationship between acoustic emission characteristic parameters and strain, stress and damage variable of rock under different failure models, the tests have been made to obtain the characteristics of acoustic emission of sandstone, leptynite, granite and limestone using hydraulic-pressure servo testing system RMT-150C and acoustic emission instrument SAEU2S under the uniaxial compression. Results have shown that the cumulative acoustic emission ring-down count of rocks with brittle or brittle-ductile failure model increases sharply before the peak stress, while accumulative ring-down count of rock with ductile failure model surges before a quiet period, which can be considered as a precursor for entering failure phase. With time being intermediate variable, the relational model between cumulative acoustic emission and strain generated from rock with brittle, brittle-ductile and ductile failure has been set up, and the coupled relation among cumulative acoustic emission, damage variable and stress has been deduced based on the Weibull distribution constitutive model. Proved by the test data, the precision of constitutive model with brittle, ductile failure is higher, which can provide accurately the basis for rock damage assessment. Related Articles | Metrics

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Stress distribution of coal pillar with gob-side entry driving in the process of excavation & mining ZHENG Xi-Gui, YAO Zhi-Gang, ZHANG Nong Journal of Mining & Safety Engineering    2012, 29 (4): 459-465.   Abstract （7420）      PDF（pc） （676KB）（5585）       Knowledge map    Save The stress distribution of coal pillar with different width in the stage of excavation and mining was studied based on the theory analysis, numerical simulation, engineering practice, the similarities and differences of stress evolution of coal pillar and entity sidewall caused by different width of coal pillar was analyzed. The opinion was put forward that the infection of roadway driving and coal mining need considered simultaneously when determination the reasonable width for coal pillar. The results show that the proper width of coal pillar should large than six meters for the deformation is attenuation with the increased with of coal pillar. However, the increased width coal pillar such as eight meters not only have reduced contribution ratio to control the sidewall deformation in the stage of coal mining, but also caused top and floor deformation increased. Therefore, the reasonable width of coal pillar is eight meters. Related Articles | Metrics

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Arrangement and support technology of open-off cut along gob area in fully mechanized caving face JIANG Li-shuai, MA Nian-jie, ZHAO Zhi-qiang, JIA Hou-sheng Journal of Mining & Safety Engineering    2014, 31 (1): 22-27.   Abstract （3996）      PDF（pc） （603KB）（5189）       Knowledge map    Save Open-off cut along gob area of fully mechanized caving face has the characteristics of large span, large thickness of top coal, small coal pillar along gob area, soft surrounding rock and fracture development, so, its support is difficult. In this paper, in view of the open-off cut along gob area with 8 m in width, and 5.6 m in thickness, by using theoretical analysis, numerical simulation, field test and monitoring analysis, the remaining principle of coal pillars and pillar stress distribution characteristics were studied, and the coal pillar width was optimized. In addition, the support mechanism of open-off cut along gob area was analyzed, and the supporting schemes including the anchor net belt combined with anchor cable, and the anchor net belt with truss and anchor rope were designed and tested. The results show that the rational width of coal pillar is around 4~5 m, and the two supporting schemes of anchor net belt combined with anchor cable and truss and anchor rope, respectively, can improve the forced state of top coal and the bearing capacity of surrounding rock, effectively control the bed separation, fracture propagation, bending and subsidence of large span and thick top coal, and ensure the stability of open-off cut along gob area of fully mechanized caving face. Related Articles | Metrics

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Numerical Simulation for Determining the Safe Roof Thickness and Critical Goaf Span ZHANG Min-Si, ZHU Wan-Cheng, HOU Zhao-Song Journal of Mining & Safety Engineering    2012, 29 (4): 543-548.   Abstract （8300）      PDF（pc） （537KB）（5055）       Knowledge map    Save In order to determine the relationship between goaf roof thickness and critical span, an iron ore goaf is taken as an engineering instance. The rock mass mechanical parameters are obtained from the mechanical experiments of rock specimens sampled in situ. The relationship between the safe roof thickness and the critical goaf span is determinined according to K. B. Lu Peinie equation, ratio of thickness and span equation, structure mechanics of girder and plate beam equation. Meanwhile, the damage and failure process of goaf roof is simulated by RFPA numerical simulation program. The relationship between the safe roof thickness and the critical goaf span is determined, respectively, when the initial damage and instability of goaf roof are adopted as the criteria. The values predicted with K. B. Lu Peinie equation are most close to the numerical ones when the damage of roof begians. The ratio between them can be considered as a safety factor obtained from the numerical simulations. As it shows, it is kept a large safety factor by the critical roof thickness which is calculated by K. B. Lu Peinie equation. The numerical simulation with RFPA could obtain this safety factor, and it may have more extensive applicability. Related Articles | Metrics

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Studies on Establishment and Application of Microseismic Monitoring System in Hongtoushan Copper Mine LIU Jian-Po, SHI Chang-Yan, LI Yuan-Hui,et al Journal of Mining & Safety Engineering    2012, 29 (1): 72-77.   Abstract （6022）      PDF（pc） （624KB）（4592）       Knowledge map    Save In this paper，in view of the serious conditions of ground pressure (rock burst，etc) appeared in Hongtoushan copper mine，we established a microseismic monitoring system in the mine，and analyzed the relationship between the microseismic activities and mining operation，and the spatial distribution of microseismic events，applied the energy index and apparent volume to forecast the occurrence of large scale rock fracturing．The location results using manual fixed-point blasting show that the location error of microseismic monitoring system is less than 10m，which suggests that the system can reach the requirement for ground pressure disaster monitoring in mine．Microseismic activities can be divided into two quiet periods and three active periods．There exits the incubation and early-warming periods before the large scale rock fracturing．The quick drop of energy index and the continuous increase of apparent volume can be used as the precursory characteristics of rock burst and large scale rock fracturing．Through the cloud charts of energy index and displacement，the potential danger areas of ground pressure disasters can be judged，which can be used to guide the safety management and ensure safety production in deep mine． Related Articles | Metrics

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Study on Influence of Temperature on Anchorage Performance of Resin Anchored Bolt HU Bin, KANG Hong-Pu, LIN Jian, CAI Jia-Fang Journal of Mining & Safety Engineering    2012, 29 (5): 644-649.   Abstract （5782）      PDF（pc） （506KB）（4585）       Knowledge map    Save To analyze the phenomenon that anchoring force of resin anchored bolt often decreased where rock bolting was carried out in the roadway near spontaneous combustion region, we studied the influence of temperature on anchoring performance of resin anchored bolts in this paper, by using the comprehensive research of laboratory test and numerical simulation. The results of pull-out tests of resin anchored bolts under different temperatures show that temperatures have great influence on anchorage performance of resin anchored bolt. The anchoring force is the largest when the temperature is 25℃, and the anchoring force descends obviously with the borehole temperature increases. Additionally, FLAC3D was adopted to simulate and analyze the anchorage system of single bolt support small-scale, and the results show that the coupled multi-physics processes exist to a certain extent between the stress field and temperature field of rock mass. The stress distribution states of rock mass are different under the same external load when the temperatures of heat source are different. On the basis, we find that the temperature variations have a certain effect on physical and mechanical properties of rock mass and curing reaction process of resin capsules, and put forward the technological approaches to ensure supporting effect under different temperatures. Related Articles | Metrics

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Study on Correlation among Point Load Strength, Compression and Tensile Strength of Coal Samples SU Cheng-Dong, TANG Xu, NI Xiao-Ming Journal of Mining & Safety Engineering    2012, 29 (4): 511-515.   Abstract （6553）      PDF（pc） （479KB）（4518）       Knowledge map    Save A series of uniaxial compression test, Brazilian test, crushing compression test and point load test on coal samples from Zhangcun mine 3# coal seam were carried out. The results show that the dispersion degree increases by the following order: Brazilian test, uniaxial compression test, and point load test. After the irregular samples compared to the regular samples，the dispersion degree of point load test is obviously too large. Among all those regular samples, the point load strengths are roughly the same by parallel bedding and vertical bedding loading methods. There is a correlation among the Protodyakonov's coefficient, uniaxial compression strength, tensile strength and point load strength of the coal samples, which could obtains relevant parameters by their interconversion, and the conversion strength can be used as a reference of coal classification strength index. Related Articles | Metrics

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Large Deformation Mechanism of Roadway Driving Along Goaf under Unstable Overlying Rock Strata ZHANG Yuan, WAN Zhi-Jun, LI Fu-Chen Journal of Mining & Safety Engineering    2012, 29 (4): 451-458.   Abstract （5962）      PDF（pc） （618KB）（4492）       Knowledge map    Save In order to grasp the large deformation mechanism of roadway driving along goaf under unstable overlying rock strata, the digital panoramic borehole camera system was adopted to observe the roof rock strata of the roadway driving along goaf. Count Fracture Numbers in a Basic Measuring Scale Method was proposed to undertake borehole fracture statistical analysis. According to the method, the fractures in the roof of the roadway driving along goaf were statistically analyzed; fractures distribution as well as the evolution law was also investigated. Observation results indicate that longitudinal fractures and transverse fractures are two major fracture forms in roof rock strata. As for the distribution, the longitudinal fractures are mainly found on the top of the roof strata in the roadway, while the transverse fractures distribute in the bottom of the roof strata along goaf. As the stabilization time of the overlying strata of the goaf went by, the longitudinal fractures gradually evolved into fracture zone, and the transverse fractures evolved into roof separation zone and radial dislocation. When the two forms of fracture cross together, a wide range of abnormal fracture zone would come into being very easily. The field observation confirms that the primary causes of the overlying strata deformation of the roadway driving along goaf are the fracture of the main roof, the rotating of the key block and its sinking and slippage. Therefore, in order to control the rotating and slippage of the key block after the fracture of the main roof will be a fundamental method to control the deformation of the roadway driving along goaf. Related Articles | Metrics

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Failure Mechanism and Control Measure of Roadway Deformation with Fractured Surrounding Rock in Deep Mine FANG Xin-Qiu, ZHAO Jun-Jie, HONG Mu-Yin Journal of Mining & Safety Engineering    2012, 29 (1): 1-7.   Abstract （4876）      PDF（pc） （656KB）（4371）       Knowledge map    Save To solve the support problem of fractured surrounding rock roadway in deep mine，based on the geological conditions of west track haulage roadway in Xuehu coal mine，we established the mechanical model of roadway floor heave，and studied the failure characteristics and influence factors of the surrounding rock in this paper．The results show that the fractured surrounding rocks around two sides of the roadway have natural pressure relief effect which can delay the formation of floor heave．With the compaction of surrounding rocks in the two sides，the stress continues to transfer toward the floor which then initiates the floor heave．Hereby，the secondary support technology is proposed to control the roadway deformation with fractured surrounding rock in deep mine，that is to say，the U-steel yieldable support is adopt as the first support，while the bolt-grouting and bolt-beam-net-anchor cable support are adopt as the second support．The greatest characteristic of the technique is altered from the lagging grouting to timely grouting，which provides a platform for exerting the anchorage effect of bolt，and the support efficiency is improved greatly．The final support parameters are determined by numerical simulation optimization，and have applied to the field industrial test．The observation results show that the roadway deformation is controlled effectively，and has obtained great social and economic benefits． Related Articles | Metrics

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Measurement of Effective Drainage Radius Based on Gas Flow and Pressure of Boreholes YU Tao, LU Ping, SUN Jin-Hua Journal of Mining & Safety Engineering    2012, 29 (4): 596-600.   Abstract （5619）      PDF（pc） （438KB）（4350）       Knowledge map    Save  In order to measure effective drainage radius exactly, we propose the method based on gas flow and pressure of boreholes. Under the index of remnant gas pressure less than 0.74 MPa and pre-drainage rate more than 30%, the computing formula is deduced based on the negative exponent attenuation law of gas flow, and the effective drainage radius is determined in combination with the variation of gas pressure. The method is applied in the arrangement of zonal pre-drainage boreholes. The effective drainage radius of different pre-drainage time and the utmost pre-drainage time are analyzed. Based on the premise that effective drainage radius reaches to 2.5 m in 90 pre-drainage days, the boreholes are designed to eliminate coal and gas outburst. The measurement method is demonstrated valid in outburst elimination by the examination of remnant gas pressure,pre-drainage rate and the zonal verification during the coal roadway driving. Related Articles | Metrics

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Research on Deformation Failure Characteristics of the Deep High-stress Soft Rock Roadways MENG Qing-Bin, HAN Li-Jun, QIAO Wei-Guo Journal of Mining & Safety Engineering    2012, 29 (4): 481-486.   Abstract （4845）      PDF（pc） （561KB）（4268）       Knowledge map    Save Based on the engineering background of Tangkou Mine, affiliated to Jibei Mining Area, the basic geological characteristics of the deep high-stress soft roadway are illustrated on the basis of geological mechanical test. According to the visco-elastic analysis of the Burgers model on deep high-stress soft rock roadway, the expressions of surface displacement and displacement rate of surrounding rock in deep high-stress soft rock roadway are obtained, and the curves of surface displacement and displacement rate of surrounding rock in deep high-stress soft rock roadway under the different geo-stresses, elastic modules and viscosity coefficients are achieved. FLAC3D is used to simulate the rheological cha-racteristics, analyzing the deformation features of the roof, floor and two-sides of the surrounding rock under high-stress. Related Articles | Metrics

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Strata Behavior and Control Countermeasures for the Gob-Side Entry Retaining in the Condition of Large Mining Height XUE Jun-Hua, HAN Chang-Liang Journal of Mining & Safety Engineering    2012, 29 (4): 466-473.   Abstract （5540）      PDF（pc） （594KB）（4235）       Knowledge map    Save Combined with the production conditions of 24207 working face in Shaqu mine, distribution characteristics of roofs stress for gob-side entry retaining influenced by mining height was studied by the method of theoretical analysis and numerical simulation. Gob-side entry retaining is in the area of stress decreasing zone of bearing pressure area. The impact scope and range to the rock gets more widely with the increase of mining height of working face. Acute deformation will occur during the mining period for gob-side entry retaining, and the contraction of area will reach to 55.3% in the condition of large mining height. Effective supporting measures are required according to the deformation characteristics of each side in gob-side entry retaining. The optimal cross-height ratio and the high strength supporting system with the core of high pre-stress could be helpful to control the deformation of surrounding rock reasonably. The observation data shows that the violent mining influence extent to gob-side entry retaining is the ranges from working face to the rear of 200 m, which is similar to the length of working face in the industrial experiment. The deformation continues to grow and roof pressure continues to increase until the length extents 250 m the strata behaviors tends to stable. Related Articles | Metrics

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Experimental Research on the Failure Characteristics of Surrounding Rock Under high Ground Stress of λ<1 State LUO Feng, YANG Ben-Sheng, SUN Li-Hui Journal of Mining & Safety Engineering    2012, 29 (4): 497-504.   Abstract （5976）      PDF（pc） （1151KB）（4222）       Knowledge map    Save By using independent researched and developed CM60/10 plane strain test-bed, combining with the triaxial servo test machine which playing the servo regulator performance, utilizing similar material simulation and numerical simulation, the characteristics of deformation and failure process of roadways with no support under high stress of  <1 state was analyzed. The results show that: 1) The destruction develops first from the center line of both sidewalls of roadway, after the local failure, there gradually formed a pair of “wedge” failure zone. In the stress relief area, surrounding rocks are destroyed in the form of zonal disintegration. Deep slip-line takes place from the tip point of the “wedge” destruction zone, which conforms to the logarithmic spiral line roughly; 2) In the process of roadway destruction, it is followed successively by three partitions of “wedge-shaped destruction zone,” “second destruction zone,” “transfixion instability zone”. The related studys show that during the different deformation period in this kind of ground stress, the failure control should focus on the sidewalls, the skewback and the roof except the control of the initial deformation of roof and floor; 3) Through the numerical simulation of the rock mass failure in  <1 state, the following results can be found: the vertical stress of the sidewalls is the “wave-like” distribution; the plastic damage zone is “partition evolution”; the vertical displacement is “jaggies-like” distribution. All of these are consistent with the physical experiments. Related Articles | Metrics

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Numerical Simulation on Mine Gas Explosion in Different Gas Content CHEN Xian-Feng, ZHANG Yin, XU Xiao-Jiang Journal of Mining & Safety Engineering    2012, 29 (3): 429-433.   Abstract （5091）      PDF（pc） （884KB）（4161）       Knowledge map    Save In this paper, to research the propagation rule and inherent mechanism of premixed flame in pipeline, we established the mathematical model and physical model by using numerical simulation method, and conducted simulation research on the process of mine gas explosion in different gas content. The calculation results show that both the velocity and pressure in gas explosion process experience the stages of “rise - fall - second wave - fall - swing”. In the initial stage of the flame propagation, the deflagration volume of gas increases rapidly, and the velocity, pressure and temperature of the flame also rise up quickly, and present laminar burning state during a certain time. Then, both the velocity and pressure have appeared swings in various degrees, which are the results of concurrent effects of pressure wave and reflected wave. Meanwhile, the velocity of the flame achieves the peak value ahead the pressure, this is mainly attributed to the superimposition of explosion pressure wave and reflected pressure wave, which leads to the rise of pressure, while the reflected pressure wave leads to the decrease of ve-locity. The best content of mine gas is that the velocity and pressure are in the minimum value, and the gas burning lasts the longest time, in this time the mine gas hasn’t been completely accelerated, and haven’t formed the detonation state. Related Articles | Metrics

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Adsorption-desorption characteristic on deformed coal under the conditions of high temperature and pressure and equilibrium Water SONG Zhi-Min, LIU Gao-Feng, YANG Xiao-Na Journal of Mining & Safety Engineering    2012, 29 (4): 591-595.   Abstract （4935）      PDF（pc） （382KB）（3929）       Knowledge map    Save Under the conditions of high temperature and pressure and equilibrium water, the adsorption-desorption experiments on CH4 were carried out with four destructive type of coal samples in No.12 Mine of Pingdingshan. The experiment results show that the equilibrium moisture of coal samples increase with the increasing extent of the coal damage in the conditions of 50℃. There are some new features on the adsorption-desorption of deformed coal，Langmuir volume of the VL (ash-free basis) first decreases and then increases, and decreases finally. Therefore, the characteristic of results of this adsorption-desorption experiments are due to the combined effects of the unique pore structure of deformed coal and water content. The adsorption-desorption isotherms of deformed coal are irreversible, and this irreversible degree increases with increasing extent of the damage of coal. The data selected by adsorption experiments should not be straightforward used in the desorption experiments on a coal, especially deformed coal. Related Articles | Metrics

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Key Construction Technology of Vertical Feeding Bore Hole for Solid Materials in Backfilling Coal Mining Ju-Feng, ZHANG Ji-Xiong, AN Bai-Fu Journal of Mining & Safety Engineering    2012, 29 (1): 38-43.   Abstract （4648）      PDF（pc） （474KB）（3925）       Knowledge map    Save   To increase the construction speed and hole quality of vertical feeding bore hole for solid materials in backfilling coal mining，based on analyzing the structure characteristcis of vertical feeding system，we analyzed the technological difficulties in drilling of vertical feeding system，and studied a set of construction techniques including the job practice，the pipeline installation，the method of inclination surveyor，et al．The results show that when using the technology which covers multistage drilling and chambering method，heavy crane or frame crane and float panel sinking method，and a variety of lateral deformation methods，the construction quality of vertical feeding system can be guaranteed．The technology has been successfully applied to a coal mine in China，while the bore hole driving speed can be reached to about 6 m/d，and the verticality is 1‰． Related Articles | Metrics

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Application of Support Technology With High Strength and High Pretension Stress for Weak-Broken Rocks WANG Hong-Wei, JIANG Yao-Dong, ZHAO Yi-Xin Journal of Mining & Safety Engineering    2012, 29 (4): 474-480.   Abstract （4652）      PDF（pc） （523KB）（3847）       Knowledge map    Save Due to high stress and low rock strength environment, the support of weak-broken rocks under the condition of deep mining should be solved through strengthening broken rock, reinforcing support resistance and decreasing the mine-induced stress. For the purpose of permanent support for the weak-broken rocks, this study has pointed out the support technology with high strength and high pre-tension stress which is based on the bolt-wire-shotcrete system combined with steel arched yielding support. This kind of support technology have combined the each support element and adequately taken advantage of load-caring capacity of surrounding rocks. Based on the monitoring data of Xiaokang coal mine and Muchengjian coal mine, the characters of weak-broken rocks and the features of the support technology with high strength and high pretension stress were analyzed. The results of field tests indicate that the support technology with high strength and high pretension stress has provided powerful support force to resist large deformation of weak-broken surrounding rocks for the various geological conditions. It is proved that the mine-induced stress can also be released by the support technology and the support technology with high strength and high pretension stress has economical significance. Related Articles | Metrics

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Coupled Thermal-Hydrological-Mechanical Analysis of Exploiting Coal Methane by Heat Injection ZHANG Feng-Jie, WU Yu, MAO Xian-Biao Journal of Mining & Safety Engineering    2012, 29 (4): 505-510.   Abstract （4908）      PDF（pc） （457KB）（3831）       Knowledge map    Save Improving coal methane production  is an important subject in the current research for coal methane exploration.Some researches show that, coal methane exist mainly as adsorption state in coal seam pores.Improving coal seam temperature can make gas change into free forms from adsorption forms,and improve its seepage-diffusion ability. According to the thermoelasticity, nonlinear Darcy seepage theory and porous medium thermodynamics principle, this paper studied the mechanism of improving coal methane production by heat injection. The multiphysical coupling equations were been established, including coal deformation equation,gas percolation equation and heat transfer equation. By means of COMSOL numerical software ,the numerical solution of coupling model was been proceeded .The results demonstrated that rising injecting heat could promote desorption of coal methane, improve the permeability, achieve the purpose of improving coal methane production. The research results could provide corresponding theoretical basis for engineering practices of exploiting coal methane by heat injection. Related Articles | Metrics

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Large-size Test on Creep Characteristics of Filling Body beside Roadway for High Water Material SUN Chun-Dong, ZHANG Dong-Sheng, WANG Xu-Feng Journal of Mining & Safety Engineering    2012, 29 (4): 487-491.   Abstract （4977）      PDF（pc） （492KB）（3730）       Knowledge map    Save Aiming to the creep characteristics of the high-water material for filling body beside roadway, we conducted several experiments by means of a self-developed large-size test system (1500 mm×600 mm×900 mm) and numerical simulation software FLAC3D. The characteristics of the deformation and the stress of the filling body sample changing over the time were analyzed during the creep process which could be divided into three stages, instant, stable and accelerating, i.e., the limit loading of the filling body increases with the reduction of water-concrete ratio for the high-water material. Due to the great deformation speed during the accelerating creep stage, the filling body should stay at the instant creep stage for long-term stability. Generally, we believe that the appropriate loading on the filling body is not less than 70%~80% of its strength. Related Articles | Metrics

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Study on Distribution of Gas Flow Fields in 1201-Face Under the Condition of Mining DONG Gang-Feng, HU Qian-Ting, WANG Zhen Journal of Mining & Safety Engineering    2012, 29 (4): 581-585.   Abstract （5225）      PDF（pc） （546KB）（3720）       Knowledge map    Save To master the distribution laws of gas flow fields is the premise of designing reasonable project for goaf gas extraction. Disallowed gas concentration occurred in return Air occurred at 1201-Face in WU Hu-shan mine. So studying the gas distribution was necessary. On the basis of gas emission analyzing, the distribution of gas flow fields in 1201-face under the condition of mining was researched by FLUENT numerical software. The difference of gas emission at the normal recovery and roof weighting periods was rationally explained. And theory basis was provided by the results to design reasonable project for goaf gas extraction. The research conclusion was verified scientificly and reliably by the field measured results. Related Articles | Metrics

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Determination on Reasonable Malposition of Combined Mining in Close-Distance Coal Seams YANG Wei, LIU Chang-You, HUANG Bing-Xiang Journal of Mining & Safety Engineering    2012, 29 (1): 101-105.   Abstract （4726）      PDF（pc） （488KB）（3660）       Knowledge map    Save Under the condition of combined mining in close-distance coal seams in Shigejie coal mine，to avoid the influence of roof periodic weighting on the lower coal seam during the mining process of upper seam，or the interaction of synchronized weightings between the upper and lower seams，we gives the selective method of determining the reasonable malposition in combined mining in this paper，by using the theories of semi-infinite elastic and underground pressure，and the field measurement data．The results show that：1) firstly，the malposition distance can be determined initially according to the mine geology and physical mechanical properties；2) then，the malposition should be modified after the theoretical analysis or field measurement of stress distribution zone between layers；3) finally，the reasonable malposition is determined ultimately by the examination of the field practice．According to the analysis results，selecting the sum of initial malposition and horizontal range value of the main stress effect zone between layers as the reasonable malposition distance in close-distance coal seams，can make the lower seam avoid bearing the continuous high stress from the upper seam． Related Articles | Metrics

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Research on Response Characteristics of Bolt Pretension on Supporting Effect of Rock Roadway in Coal Mine CHANG Ju-Cai, XIE Guang-Xiang Journal of Mining & Safety Engineering    2012, 29 (5): 657-661.   Abstract （5049）      PDF（pc） （463KB）（3644）       Knowledge map    Save In this paper, to theoretically demonstrate the action mechanism of bolt pretension on supporting effect of roadway, the ideal elasto-plastic strain-softening model is established to analyze the mechanical characteristics of bolt supporting in rock roadway. Thus, the analytical expressions of displacement, stress distribution in roadway surrounding rock after pre-stressed bolt supporting are obtained. The theoretical analysis results show that improving the bolt pretension can improve the stress states of surrounding rock around the roadway and control the roadway deformation effectively, which is beneficial to maintain the roadway stability. Moreover, the influence relation of bolting pretension on roadway supporting effect is further studied based on field measurements. The research results can provide theoretical basis for analyzing the bolting action mechanism and bolt supporting design. Related Articles | Metrics

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Fractal characteristics of porosity for porous media in coal mass LI Zi-wen, LIN Bai-quan, HAO Zhi-yong, GAO Ya-bin, LIU Fei-fei Journal of Mining & Safety Engineering    2013, 30 (3): 437-442.   Abstract （2713）      PDF（pc） （249KB）（3635）       Knowledge map    Save Coal is a kind of porous media, in which the pore structure is very complex. Thus, the accurate evaluation of the pore characteristics of coal mass has great significance to research the adsorption and desorption of gas and the efficient gas drainage. In this paper, based on fractal theory, a kind of random fractal model which can be use to describe the pore space distribution of porous was researched, and on the basis of its construction method, the relationship between porous media porosity and fractal dimension was established. In addition, by mercury injection experiment, the correctness of fractal model was verified, and the fractal description of porosity for porous media of coal mass was carried out. The results show that porosity is determined by fractal dimension, and the porosity decreases with the increase of fractal dimension. Meanwhile, the smaller the observing scale, the bigger the porosity, the smaller the average diameter of the same order pore, the smaller the porosity, and the less the amount of the same order pore, the smaller the porosity. Moreover, the pore size distribution can be different with the same porosity, which leads to different gas flow, and adsorption and desorption laws. Therefore, the fractal dimension can reflect the characteristics of pore size distribution in coal mass, which has great significance to the study of pore types of coal mass and gas flow in the coal seam. Related Articles | Metrics

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Research on Floor Heave Mechanism of Thick Seam Roadway in Wuyang Coal Mine and Its Control YANG Ben-Sheng, GENG Xue-Liang, SUN Li-Hui, SONG Xian-Zhong, ZHANG Li Journal of Mining & Safety Engineering    2012, 29 (1): 8-13.   Abstract （4712）      PDF（pc） （561KB）（3568）       Knowledge map    Save In view of the frequent large deformation failures of the extraction roadway floor in thick seam 76#-2 in Wuyang mine，we proposed the prevention concept of medium and deep strengthening in thick seam roadway to control floor heave，through studying on the mechanism and control method of the floor heave in thick seam roadway．Additionally，the effects to the floor under different supporting ways were simulated by FLAC3D software. The results show that the floor deformation without supporting is 1.3~1.6 m，but the floor damage zone will be extended gradually under the mining stress disturbance．The floor plastic zone will be reduced correspondingly by the support of anchor coupled with the grouting，but the maximum value of floor deformation amount to 0.7~1.0 m when influenced by mining stress，and the roadway still can’t meet the production needs．By using the combined support of a branch of high-strength anchors coupled with concrete block and grouting，the plastic zone in floor surrounding rock will be reduced significantly，and the floor heave is only 0.24~0.38 m，which has met the requirements to control the floor deformation．Through the engineering tests of the combined support technique，the result shows that the two sides’displacement and floor heave of the roadway are 226 mm and 283 mm，which are reduced by 56.5% and 83.4%，respectively．Thus，the large-scale deformation of roadway floor in thick seam has been controlled effectively． Related Articles | Metrics

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Experimental test of methane solubility in surfactant aqueous solution YANG Yong-Liang, LI Zeng-Hua, HOU Shi-Song, SUN Liu-Tao, LIU Zhen, TANG Yi-Bo Journal of Mining & Safety Engineering    2013, 30 (2): 302-306.   Abstract （2507）      PDF（pc） （211KB）（3563）       Knowledge map    Save During the process of coal seam water infusion or roadway spray, if the aqueous solution is modified so that it can absorb mathane gas well, the gas content of coal seam will be effectively reduced, and the outburst danger of coal seam may be eliminated. In this paper, the experimental device for methane dissolution was developed and processed, and the methane dissolution experiments under different temperatures, concentrations and pressures were conducted by selecting different surfactants with stong solubilization capacities. The results show that the methane solubility increases mainly in logarithmic way with the growth of gas concentration and gas pressure, and decreases exponentially with the increase of temperature. In addition, the solubility data of polypropylene glycol (PG) is largest among the four kinds of surfactants. The data can reach to 24.66 mL/100 mL in 10% PGM solution at normal temperature and pressure, which is 7.45 times to the pure water. In conclusion, the order of solubilization capacities among the four types of surfactants is: PG> Polyvinyl> THF> F-500. According to the experimental results, the calculation equation of methane solubility under different conditions was established, and the estimated values agree well with the experimental values. The results can provide reference to improve the effects of gas control by using hydrodynamic hydraulic measures in coal mines. Related Articles | Metrics

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The Relationship Between Permeable Fractured Zone and Rock Stratum Tensile Deformation GAO Yan-Fa, HUANG Wan-Peng, LIU Guo-Lei Journal of Mining & Safety Engineering    2012, 29 (3): 301-306.   Abstract （4270）      PDF（pc） （505KB）（3520）       Knowledge map    Save To research the relationship between crack stratum’s hydraulic conductivity within permeable fractured zone and tensile deformation of rock stratum, the concept of interlayer stratum was defined first in this paper, then the formula of strata tensile rate ε was deduced, by assuming that two sect of arcs can be used to fit inside and outside brim curve of subsidence trough, and the statistical results of field observation of permeable fractured zone height were obtained at last. The results show that when the tensile rate ε of the interlayer stratum surpasses its deformation limit, the normal tensile crack will be generated, and when ε is larger than the limit rate, the crack stratum will become the hydraulic conductivity stratum. In addition, the layer tensile rate ε depends on layer’s height (h), mining thickness (m), stratum’s subsidence ratio (q), boundary angle (δ0) and full mining angle (ψ), and so on. According to the regression analysis of some coal mine’s permeable fractured zone heights, the harder the upper strata is, the larger the ratio of fractured zone height to mining thickness（H-T ratio）is, and the smaller the layer tensile rate of top stratum within water flowing fractured zone is. Related Articles | Metrics

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Structure Forms of Basic Roof and Reasonable Supporting Parameters in Ends of Fully- Mechanized Top Caving Face YANG Pei-Ju, LIU Chang-You Journal of Mining & Safety Engineering    2012, 29 (1): 26-32.   Abstract （3840）      PDF（pc） （783KB）（3382）       Knowledge map    Save  The determination of face-end hydraulic support resistance is the key to support design and selection．Therefore，theoretical analyses were carried out in this paper to study the collapse of overburden，movenment rules of basic roof structure，and determination method of resonable supporting parameters in the face-end area．The results show that the basic roof can be the fractured or caving rock stratum in the face-end area．The sinking motion of the arc triangular pieces in the fractured zone is the same with the voussoir beam in the middle of the face，while the arc triangular pieces in the caving zone can be regarded as the cantilever beam which is only supported by coal wall and loaded by overburden pressure，or forms the similar voussoir beam structure hinged with the frontal and posterior arc triangular plates mutually．Different triangular plate structures of main roof result in different pressure behavior，that is，the pressure behavior of main roof is obvious in the voussoir beam structure，and the dynamic load coefficient is large，while the similar voussoir beam hinged by triangular plate structures results in less pressure behavior and smaller dynamic load coefficient．In the action relation between the support and surrounding rock in the face-end，the working conditions of support include three types：given deformation state，limited deformation state，and given loading state．Meanwhile，the reasonable supporting strength of face-end support under different conditons can be estimated by the corresponding voussoir beam，cantilever beam，and the similar voussoir beam hinged by triangular plate structures in the face-end area，respectively． Related Articles | Metrics

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Theory and Applicable of Yield Mining at Ending Stage of Fully-Mechanized Face in Shallow Seam at Shendong Mine Area WANG Xiao-Zhen, JU Jin-Feng, XU Jia-Lin Journal of Mining & Safety Engineering    2012, 29 (2): 151-156.   Abstract （4518）      PDF（pc） （820KB）（3372）       Knowledge map    Save According to the problem of support crushing accidents at the ending stage of fully-mechanized faces in Shendong mining area，theory analysis and practice method was adapted to research the principle and application of yield mining．The results show that yield mining is a kind of skill that can avoid the influence of ground pressure at ending stage of fully-mechanized faces by stopping mining at a proper position before removing，which can change the starting location and decrease the length of continuous pressure by reducing mining velocity and create a non-pressure surroundings．While the width of interval pillars during yield mining must be determined by taking interval pillars’ stability and non-pressure at ending stage as premise．Four probable situations are put forward according to the pressure law before stopping mining and pressure behavior during stopping mining．Yield mining was successfully used at the ending stage of NO.21305 fully-mechanized face in Daliuta coal mine and NO.22303 fully-mechanized face in Bulianta coal mine which realizing a safe waking face removing． Related Articles | Metrics

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Assessment of Water Environmental Status in Subsided Water Area of Coal Mine and Its Comprehensive Utilization XU Liang-Ji, YAN Jia-Ping Journal of Mining & Safety Engineering    2012, 29 (4): 549-554.   Abstract （4705）      PDF（pc） （416KB）（3365）       Knowledge map    Save In this paper, to accurate assess the water quality in subsided water area of coal mine, the methods of principal component analysis and fuzzy comprehensive assessment are adopted and mended to establish comprehensive evaluation model for water quality of subsided water area. 14 large-scale subsided water areas in Panji mining area of Huainan have been chosen to layout sampling sites and conduct sampling and monitoring for assessing the pollution status of water quality in subsided water area. The assessment results show that variance contribution rate of PC1 (first principal component) has been increased significantly after being improved, and enhanced to 98%. When the variance contribution rate of PC1 has exceed 85%, the whole indexes of PC1 are chosen as evaluation factors of fuzzy comprehensive assessment model to assess water quality, the assessment results show that all of subsided water areas have been polluted in various degree. Because the unified evaluation indexes have been chosen to assess water quality, the assessment results of the same type subsided water areas are comparable, and the results can be used as the foundation data for programming and utilizing subsided water resources and constructing “plain reservoir” in Huainan. Related Articles | Metrics