Table of Content

15 January 2013, Volume 30 Issue 1

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Inhomogeneous damage and sealing support of roadways through thin bedded coal-rock crossovers

ZHANG Nong, LI Bao-Yu, LI Gui-Chen, QIAN De-Yu, YU Xian-Yang

2013, 30(1):  1-6. 

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Roadways are usually constructed in thin bedded coal-rock crossovers and subjected to asymmetric and inhomogeneous damages. Application of conventional unsealing symmetric supporting shows poor performance and worse long-term maintenance effect. Taking the frequent crossover-through roadway construction of Suntuan coal mine as an engineering example, we summarize its typical asymmetric and inhomogeneous damage features, such as shoulder angle fracture, large sidewall deformation, floor heave and whole section instability etc, and analyze its main influential factors. Whole section sealing support was mainly constructed by active support such as anchor, bolt and grouting, assisted by other structure supplement. Inhomogeneous damage of roadways in thin bedded coal-rock crossovers could be controlled by combination of prestress synergy function of anchor and bolt, interaction strengthen of surrounding rocks and grouting, structure supplement of leg-locked equipment and U type shed. Whole section strengthening was implemented through bolt-shed-grouting on roof and sidewall, continuous restraint on arch and bolt-grouting on floor. The technology has been successfully applied in a 570 m deep roadway in coal-rock crossovers, whose deformation was controlled between 180 mm and 220 mm, guaranteeing of construction safety and long-term stability.

Stability analysis and mechanism of two-side anchorage body in deep mine gateway

GOU Pan-Feng, XIN Ya-Jun, SHEN Yan-Mei, ZHANG He

2013, 30(1):  7-13. 

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Through analysis of failure characteristic and mechanism on two-side anchorage body in deep mine gateway，we get most serious failure spot of two sides in middle-upper part．Bolting function is to form anchorage body structure because of the force between bolt and rock in anchorage range．The instability of two-side anchorage body in deep mine gateway is divided into fracturing and shearing instability，and first instability form of two-side anchorage body is fracturing instability．The paper establishes stability mechanical model of two-side anchorage body in deep mine gateway under two instability forms，which provides bolt and cable couple-support scheme and carries out mechanical calculation，numerical analysis and field observation on test gateway．After carrying out support design scheme on gateway two sides，two-side convergence amount decreases. The largest displacement amount is 124 mm，which is controlled in reasonable range. Two-side surrounding rock is stable，and the support effect is remarkable．

Research on the dynamic evolutionary of rock rheology in soft rock with high ground stress

WANG Cheng, WANG Liang-Hai, ZHANG Nian-Chao

2013, 30(1):  14-18. 

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Aimed at the rheological problems of soft rock roadway with high ground stress，rheological equations for plastic zone and elastic zone has been established which is based on Bingham rheological model．Rheological radius and stress of surrounding rock were both derived by the different time．In order to analyze the influencing factors，such as ground stress，roadway radius，support strength，grouting and so on，the -545 m south track roadway in Suntuan mine of Huaibei Mining Group was taken as a case study. The results show that rheological process of roadway surrounding rock has three stages such as rapid growth stage，slow growth stage and stable stage. As time goes by，rheology range of surrounding rock gradually extends to the deep，and the shallow stress decreases. As a result，the stress peak continuously transfers to the deep. The rheological radius increases when the ground stress or roadway radius increases. The rheological radius decreases when support strength increases. Roadway grouting can improve surrounding rock’s anti-rheological properties，which is tested by the numerical calculations and measured data in the testing field．

Roof control technology of the intersection of large section roadway during shrinking face

JIANG Yu-Lian, PAN Jun, HE Yong-Qiang, HUANG Guang-Jun

2013, 30(1):  19-22. 

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Based on the shrinking face project and roof support problem of intersection of roadway at fully mechanized top coal caving face in the No.2 Deep Mine of Pingshuo，the stress and displacement fields of surrounding rock of the roadway intersection are calculated and analyzed by FLAC3D three-dimensional numerical simulation software. By compared with site monitoring data，the rule of the intersection of roadway roof’s variation are obtained and analyzed. The result shows that the roadway height of intersection could not be ensured in the present support condition. Therefore，the roof of in-tersection should be reinforced to meet the security of support. After reinforced supporting，the roof deformation has been effectively controlled，which could ensure the roadway height of intersection during shrinking face.

Water inrush risk evaluation of coal mining under Quaternary alluvial water and reasonable design method of waterproof coal pillar

MENG Zhao-Ping, GAO Yan-Fa, LU Ai-Hong, WANG Rui, QIAO Xu, HUANG Cheng-Yu

2013, 30(1):  23-29. 

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In this paper, the concept of water inrush risk coefficient was proposed through theoretical analysis, and the theory and method of the evaluation of water inrush danger under the Quaternary loose aquifer, as well as the reasonable design method of waterproof coal pillar were established. The results show that the thickness of effective protective layer is calculated by the distance between the top of mining seam and bottom of Quaternary loose aquifer minus the height of caving and fractured zone which is formed after mining the whole height at one time. If the thickness value is less than zero, the  water in the Quaternary loose aquifer may influx into the working face, which will result in roof water inrush. If the thickness value is larger than zero, the water inrush risk coefficient, which is the ratio of hydraulic pressure in Quaternary loose aquifer to the thickness value of effective protective layer, can be used to evaluate the water inrush danger. On this basis, the thickness of protective layer and the reasonable height of waterproof coal pillar are put forward according to the hydraulic pressure value of loose aquifer. Adopting the method metioned above, the water inrush danger of No. 8 coal seam mining under Quaternary loose aquifer in Donghuantuo minefield, Kailuan mining area, and the reasonable waterproof coal pillar were evaluated. The evaluation results consistent well with the actual conditions.

Experimental study on the conversion from seepage to flow of water inrush aroused by fault activation in fully mechanized top-coal caving

QIAO Wei, HU Ge, LI Wen-Ping

2013, 30(1):  30-37. 

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In this paper, to reveal the water change process of water-inrush aroused by fault activation, based on the example analysis of water inrush through fault in the fully mechanized top-coal caving face, the similar material simulation models of water inrush aroused by fault activation under different water pressures were designed, including the coal mining under the hanging wall and foot wall of fault, respectively. Meanwhile, the variation rules of Reynolds numbers, fillings and voidage of fault zone along with time were analyzed according to the test data, and the variation rules of voidage and water inflow along with time were comparized. The results show that the water inrush aroused by fault activation in fully mechanized top-coal caving has experienced the process of pore fluid, fracture flow and pipe flow, and the time when the pore fluid converses into fracture flow（7，9，13 and 15 s）is identified according to the variation law of filling emission quantity along with time, while the time when the fracture flow converses into pipe flow（30，35 and 40 s）is obtained according to the change law of voidage along with time. The test results have explained the conversion phenomenon from seepage to flow of water inrush aroused by fault activation in fully mechanized top-coal caving, and are anastomotic with the expressive characteristics of field examples.

Modeling and microseismic monitoring of damage and failure evolution of faulty coal seam floor

LU Yin-Long, WANG Lian-Guo

2013, 30(1):  38-44. 

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Based on the elastic damage mechanics theory, a piecewise linear and elastic damage constitutive model incorporating the residual strengths under different confining pressures was constructed, and the model parameters were determined by general triaxial compression and split tension tests. In addition, taking the geology conditions in one mine as engineering background, the damage and failure evolution characteristics of faulty coal seam floor during the mining process were simulated, after the established damage model programmed by MATLAB being embedded into COMSOL. The results show that when the working face moves to the top zones of fault, the active zones of fault will connect with the failure zones in floor induced by mining, which dramatically increases the failure depth of floor, reduces the water isolating properties of the aquifuge, and increases water-inrush possibility. Finally, the high-precision microseismic monitoring technique was employed to monitor the dynamic failure characteristics of the coal seam floor, and the monitoring results are basically in agreement with the numerical results.

Integrated geophysical prospecting principle and method of explorating the water enrichment of coal mine collapse column

YANG Wu-Yang

2013, 30(1):  45-50. 

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The sizes and distribution range of collapse columns existing in Huainan mining area have been found out by 3-D seismic exploration, but the water enrichment conditions inside the columns are not clear, which greatly influences the safety mining. In this paper, the Controlled-Source Audiomagnetotellurics and Electromagnetic Wave method were adopted to prospect the water abundance of collapse columns. The result shows that the apparent formation resistivity has a certain correlation with the water abundance, that is, low resistivity is corresponding to abundant water, while high resistivity correlates with low or no water abundance. Meanwhile, the water enrichment of collapse column are analyzed according to the horizontal and longitudinal apparent resisitivity profiles in different depth, and the detection results show that the water abundance in the south of collapse column and partial areas near the faults are relatively large, namely there only exists partial water enrichment in the collapse column. A small amount of validation drillings on the ground have been constructed, and the detection results correspond well with those of drilling, which provides a new integrated geophysical method for the prospecting of collapse column in coal mine．

Research on lightweight device for blocking gangue between hydraulic supports in steeply inclined coal face

CAO Shu-Gang, LI Yi, LEI Cai-Guo, LIU Fu-An

2013, 30(1):  51-56. 

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The device for blocking gangue between hydralic supports is the important guarantee to avoid the situation that coal and gangue slide down to hurt people and destroy equipment, when assigning fully-mechanized longwall face on the strike with true-inclined or false-inclined layout in the steeply inclined coal seam. In this paper, based on assive investigation and plan comparison, a light-weight device for blocking gangue with metal net and four-door combination has been developed. The device increases the adaptability to the changes of dip angle and mining height of coal seam, and can change the advance directions of working face, by using the sliding system of ball bearing type, symmetric design and changeable size of doorframe. The numerical simulation results show that the device can meet the needs to prevent coal and gangue, the sliding system composed of guide rails, rollers and limit rails presents high flexibility, and can avoid the problem that the device for blocking gangue may fail to work under hydraulic control, after adoting manual control to close sliding door. In addition, when using metal-net frame structure in the hanging door and sliding door, can reduce the local ventilation resistance of working face, and is helpful to the ventilation stability of working face. Field tests indicate that the weight of light-weight device for blocking gangue between supports is reduced two thirds of that of the previous planer device for blocking gangue, and it is convenient to transport, install and maintain．

Study on the evaluation method of scientized mining by extension theory

LI Dong-Yin, LI Hua-Min, ZHOU Ying

2013, 30(1):  57-62. 

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 In order to promote quantitative evaluation of scientized mining，this paper proposes six connotative indexes which can inflect the scientific mining，such as safety mining，green mining，high-recovery mining，intensive & high-efficiency mining，intellectualized mining and absorption-cost mining．By the way，four extension indexes which are closely related to scientized mining as follows，resource endowments，security technology guarantee，scientific management guarantee，economic and social benefits，at last the“10-42-63”structure evaluation system of scientized mining has been built．Having discussed the relationship between scientific mining and extension theory，meanwhile，the theory based on the methods as follows: extension theory，subjective dynamic determining weights method，linear weighted integrated method and expert setting parameter method．The assessment method of the scientized mining grade is proposed，research and develop ESSM，a soft applicable to evaluate all types of underground mine，which can calculate scientized mining coefficient(ScMC)and scientized mining rank(ScMR)separately or simultaneously is founded．

Study on closed multiple-seam in the ascending mining technology

ZHANG Hong-Wei, HAN Jun, HAI Li-Xin, LI Ming, QIAO Hong-Bo

2013, 30(1):  63-67. 

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The research concerns the closed multiple seam ascending mining technology (mining induced influenced coefficient 2.7) of Qinghemen coal mine，Fuxin mining area．Theoretical analysis，numerical calculation，similar material simulating experiment and on-site exploration are applied comprehensively in the integrity and continuity of 3-3 coal seam after the 3-2 coal seam mined．Based on the stress state and structure variation of 3-3 coal seam，the roadway layout is designed．The 3-3 coal seam mining practice indicates that when the above coal seam lied on the caving zone of low coal seam，the integrity of the above coal seam could still maintain continuity and integrity，because the formation of cracks and fracture could gradually “healed”，which improved the integrity of coal to meet the conditions necessary for mining．

Research on distribution law of frozen temperature field of fractured rock mass with groundwater seepage

GAO Juan, FENG Mei-Mei, YANG Wei-Hao

2013, 30(1):  68-73. 

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A numerical calculation model of fractured rock mass artificial seepage freezing with two holes was set up，and the problem of coupling and phase change during the freezing process were simulated by using the COMSOL Multiphysics finite-element analysis software．The influence of the fracture on the distribution of freezing temperature field and seepage field was analyzed．The distribution law of freezing temperature field corresponding to the different flow velocities was researched．The results show that the existence of fracture reduces the thickness of the frozen wall in the upstream，and the isotherms outside the frozen wall show“heart-shaped”distribution．The seepage velocity has a great influence on both the frozen wall development and the closure time．If the seepage velocity is increasing，the development of freezing wall will become slower and the closure time will become longer accordingly．In this paper，when the seepage velocity is less than 7 m/d，the closure time shows a linear relationship with the seepage velocity basically．But when the seepage velocity is more than 7 m/d，the closure time mount up sharply，the closure time tends to be infinite once the velocity exceeds 10 m/d，namely reach the unable closure stage．

Strength characteristic of cemented waste rock backfills and its application

HE Gui-Cheng, LIU Yong, DING De-Xin, ZHANG Zhi-Jun

2013, 30(1):  74-79. 

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The No.2 ore body in the western district of Baoshan mine is deep-buried and hard to be mined out, thus, the filling method is adopted by using the backfills of cemented waste rock. In this paper, to ensure the mining safety, the compressive strengths of the backfills with seven different mixture ratios at different solidification durations were measured by using RMT-150B rock mechanics testing machine. In addition, the mechanical parameters for the backfills at the solidification duration of 28 days were used to simulate the mining and filling processes of test stop by using FLAC3D. Based on the simulation results, the backfills of cemented waste rock with type C mixture ratio was used to filling in the test stope, and the stress measurements were conducted for the backfills and surrounding rocks. The results show that the water cement ratio and cement sand ratio are the key factors to control the compressive strength of the backfill, and the compressive strength of the backfill with type C mixture ratio at the solidification duration of 28 days was larger than 2 MPa. Meanwhile, the maximum principal stress and maximum vertial displacement decrease with the increase of backfill strength, while the minimum principal stress is the contrary. The stress measurements of the backfills and surrounding rocks in the test stope are in good agreement with the simulation results, which means that the backfills with type C mixture ratio can be used to effectively control the ground pressure in deep stope mining.

Splitting criterion of unloading rock burst for high-stress hard rock and its sensitivity analysis of factors

ZHANG Xiao-Jun

2013, 30(1):  80-85. 

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In this paper, aiming at the existing defects of rock burst study, a splitting catastrophe model of unloading rock burst of surrounding rock was established based on the mutation theory, and the necessary and sufficient conditions of splitting rock burst were obtained while considering the unloading influence, then the sensitivity of influence factors was further analyzed. The results show that the mutation characteristic value and critical condition of rock burst were reduced obviously by excavation unloading, and the occurrence possibility of rock burst increases greatly，when the tensile stress meets the condition of σx=πσt/4, the necessary conditions will become the sufficient conditions. Meanwhile, the surrounding rock will be displaced after a period of unloading, the standard or delayed rock burst will occur when the unloading microscopic tensile stress reaches the needed condition to induce rock burst, while the instant rock burst occur will occur when the vertical stress reaches to a certain value and the mutation characteristic value of surrounding rock during unloading moment meets the condition ofΔ≤0. In addition, the splitting of rock burst should satisfy a certain size requirement of free surface, and the requirement can be reduced significantly with the increasing of vertical stress. Moreover, the vertical stress have important influence on the ΔE，σx and Δ, while the horizontal stress have more im-portant influence on the Δ.

Predication model of game theory-matter-element extension for blastability classification and its application

SHANG Jun-Long, HU Jian-Hua, MO Rong-Shi, LUO Xian-Wei, ZHOU Ke-Ping

2013, 30(1):  86-92. 

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In this paper，in order to improve the present methods of rock blastability classification，a prediction model of game theory-matter-element extension for blastability classification was established．Firstly，based on the analysis of main causes of blastbility，three indexes were chosen as the evaluation indicators and the classification standards were confirmed．Meanwhile，in order to remedy the defect of the correlation function cannot be calculated when the eigenvalue exceeds the controlled field，the blastability classification standards were normalized．Secondly，based on the game theory，the synthetic weight values of eigenvalue were determined by integrating the objective-dynamic weight and subjective-static weight，which can solve the problems occurred in traditional matter-element extension assessment method，that is，the indicator weight only depends on the eigenvalue，and ignores the significance of feature．Finally，the classification of blastability was predicted by using the maximum incidence degree criterion，and the prediction model of game theory-matter-element extension for blastability classification was proposed．The application results show that the blastability of surrounding 
rock and ore body in the roof is of medium-grade，and the surrounding rock in footwall is of relatively low-grade．The predication results agree well with the project reality geological situation，thus，the corresponding control measures about the blasting in mine engineering were put forward．

Mechanical properties of similar material under uniaxial compression and the strength error sources

LUO Feng, YANG Ben-Sheng, HAO Bin-Bin, SUN Li-Hui, FU Ming-Ming

2013, 30(1):  93-99. 

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 In this paper, in order to improve the accuracy of similar simulation experiment, we tested the stress-strain behaviors of similar material specimens with different compositions (sand-plaster, sand- cement-plaster) and proportions by uniaxial compression testing, analyzed the mechanical properties and post-peak failure characteristics, and investigated the error sources during the production of similar material models and testing of specimens. The results show that: 1) The two similar materials both show good elastic-plastic properties in the loading process, thus, they can be used to simulate different rock mass; 2) The post-peak strain-softening processes of the two materials are smooth, and the residual strengths are stable; 3) Due to the insufficient cementation and primary damage of the similar materials, abnormal pressure-relief and stress fluctuations are prone to appear in the loading process, and the main failure modes are the tensile failures and conjugate shear fracturings; 4) Human factors affect a lot during the production procedures of similar material models, thus, in order to increase the accuracy of similar material experiment, we put forward the error sources in the preparation and test processes and try to avoid them.

Reliability calculation of structure system correlated with multiple failure modes

ZHANG Dao-Bing, YANG Xiao-Li, ZHU Chuan-Qu

2013, 30(1):  100-106. 

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In this paper, the structure system with multiple failure modes were classified into the system with single limit state function and the one with multiple limit state function, then, the general reliability models and expressions for the two structure systems were also established, respectively. Meanwhile, in view of the characteristic that the reliability of structure system with multiple failure modes was usually computed by approximate estimation method and the results of calculation had some errors, we put forward a new relatively accurate method to calculate the reliability of structure system with multiple failure modes based on the Monte Carlo simulation method in MATLAB, gave the detailed calculating steps and program diagrams, and proceeded analysis combining with two examples. The results show that the calculated reliability by using multiple failure mode are more scientific and precise, compared with that computed by traditional single mode. Furthermore, the low efficiency in conventional realization process by Monte Carlo simulation method can be overcome during the new reliability calculation by using computer programs directly, the results can be calculated without the linear of performance function and normalizing of random variable, without complex conversion process, without solving the joint probability density function, and can obtain high calculation accuracy.

Uniform prediction parameters for ground movement model in mountain area caused by coal mining

HAN Kui-Feng, KANG Jian-Rong, WANG Zheng-Shuai, WU Kan, ZHANG Meng

2013, 30(1):  107-111. 

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In this paper, in view of the difficulty to choose prediction parameters of ground movement model in mountain area caused by coal mining, the solution scheme of the uniform prediction parameters for ground movement model were put forward. After colleting and analyzing the ground movement data of 14 representative observation stations in Shanxi Province, then considering the uniform prediction parameters of the model and the maximum subsidence values predicted by probability integral method as the control vector, and the maximum measured subsidence values as the output vector, the uniform prediction parameters were finally obtained, that is, A=7.63, P=1.60, and t=3.40, by using least squares nonlinear fitting optimization algorithm. The example analysis results show that the average relative errors of the predicted subsidence values and horizontal movement values were 9% and 21%, respectively, when using the uniform prediction parameters, which can meet the demands of engineering precision.

Electrical potential signals during rupture process of tunnel sandstone

LI Zhong-Hui, WANG 恩Yuan, SONG Xiao-Yan

2013, 30(1):  112-117. 

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In this paper, the variation rules of electric potential signals during fracture process of tunnel sandstone and the precursor characteristics before rupture were studied. The results show that the electric potential signals will be generated in the fracture process of sandstone, and there is close corresponding relation between the electric potential signals and deformation and fracture of the samples. Meanwhile, the potential signals are more sensitive to the deformation and failure, and the propagation of cracks at the initial stage of loading, while the acoustic emission is fewness, and the potential amplitudes slightly reduce at the later stage of loading while the acoustic emissions increase abundantly. Within 70%~97% of the peak strain in the process of accelerating deformation, there will exit strong pulse potential signals, thus, the sharply increase of potential before strain peak can be used as the precursor characteristics of sandstone rupture. Through the study of variation rules of electric potential during rock failure, it can deepen our understanding in the rock micro-fracture process which may provide basic research results for monitoring tunnel rock mass stability and construction safety by using the electric potential technology.

Effect of mass ratio change of hard and soft coal on adsorption of methane gas

LI Shu-Gang, ZHAO Peng-Xiang, LIN Hai-Fei, PAN Hong-Yu, CHENG Lian-Hua

2013, 30(1):  118-122. 

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In this paper, based on gas adsorption by the single coal body, both the hard and soft coal samples were chosed in the same air-intaking entry of one mine in Shanxi, and the samples were mixed hierarchically according to different quality ratio. In addition, the influence of mixed samples on gas adsorption characteristics under different quality ratios of hard and soft coal bodies were studied in the laboratory, by using Langmuir single molecule layer absorption theory. Then, the curves of adsorption quantity variation, the variation equation of adsorption constants a, b, and the initial speed of methane emission ΔP , with different mass ratios of hard and soft coal bodies, were obtained. Moreover, the effect of mass ratios of hard and soft coal bodies on gas emission were further analyzed. The results show that the adsorption constants a and initial speed of methane emission ΔP reach the maximum values, and the constants b reach the minimum value when the quality of soft coal is approximately equal to that of the upper hard coal. It implies that the gas adsorption quality and pressure of coal body all achieve the maximum values in this condition, and once the coal seam has been disturbed, large pressure gradient and concentration gradient will be formed, and large amount of methane gas will blow out. The research results provide theoretical foundation for the mechanism of coal and gas outburst.

Theoretical analysis and numerical simulation on protective seam extraction in Mayixi mine

ZHANG Mei-Run, YANG Sheng-Qiang, CHENG Jian-Wei, PU Rong-Fei, WANG Da-Qiang, WANG Feng-Shuang

2013, 30(1):  123-127. 

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  Gas accidents in coal mine have been considered as one of the worst coal mine disasters and often cause lots of death of miners. The protective extraction method is the most effective and regional way to prevent coal and gas outburst when multiple coal seams are mined in the outburst mine. In this paper, based on the theoretical analysis and feasibility study of applying the protective extraction tech-nique to prevent outburst during multiple coal seams mining, the protective coal seam was determined by analyzing gas occurrence characteristics of each seam and the lithology of coal formation. Meanwhile, by considering the key influence factors for the selection of protective coal seam and the practical situations in Mayixi Coal Mine, the deformation rules of coal and rock mass during the mining process of protective seam were obtained by the numerical simulation of FLAC3D. The theoretical analysis and numerical simulation results show that choosing No. 5-2 Coal Seam as the protective seam to be mined first, can greatly eliminate outburst danger for the upper and lower protected seams, and achieve the goal of outburst prevention and gas control in region.

Pressure-relief gas extraction of lower adjacent coal seam based on strata movement and its application

WANG Hai-Feng, FANG Liang, CHENG Yuan-Ping, WANG Wei, ZHOU Hong-Ru

2013, 30(1):  128-131. 

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In this paper, taking coal face 62114 in Xinzhuangzi mine, Huainan, as the engineering example, we analyzed the gas emission laws of the coal mining in the closed distance upper protective seam, and proposed the corresponding gas control measures. The results show that, 1) Under the mining disturbance of the upper protective seam, the underlying coal/rock strata can be divided into floor heave fracture zone and floor heave deformation zone in the mining influence area, and the lower protected seams under the floor heave fracture zone have the migration trends to the goaf of protective seam. 2) Y model ventilation can be used to solve gas accumulation and overflow in the upper corner of the face mining in the closed distance upper protective seam. 3) In principle, the spacing of penetrating boreholes in the lower protected seams should be less than or equal to 1 times of the seam spacing, which can just effectively prevent the pressure-relief gas of protected seams flowing into the working face of protective seam. Finally, the gas extraction results of coal face mining in the closed distance upper protective seam of Xinzhuangzi mine were analyzed.

Grouped pressure test to determine effective gas drainage radius

LIANG Bing, YUAN Xin-Peng, SUN Wei-Ji, WANG Yan, ZHAO Hai-Bo

2013, 30(1):  132-135. 

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In this paper, to accurately measure the effective radius and identify the reasonable arrangement of drainage borehole spacing, the arrangement of drilling holes in the traditional gas pressure measurement were improved appropriately. In the same height, unequal spacing of pressure measurement boreholes and drainage holes were arranged separately, the effective extraction radius was then determined by monitoring the gas pressure changes in different borehole groups, and the field test was practiced in Tingnan coal mine. The stress drop curves show that the gas around the drainage holes flows in a state of linear seepage in the early drainage period, then gradually turns to low-speed nonlinear seepage with extraction time prolonged, while the gas pressure and extraction time basically shows power function correlation in the whole curve. Moreover, the effective drainage radius reaches to 4 meters after 40 days gas extraction, and the influence scope of gas drainage expands no longer after the radius up to 5 meters.

Research on advanced compressed air self-rescue system in underground mine

ZHANG Ying-Hua, HUANG Meng-Yu, HUANG Zhi-An, GAO Yu-Kun, GU Ke-Rui

2013, 30(1):  136-142. 

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 Aimed at the defects of current compressed air self-rescue device, such as deep colour which is difficult is be found out in underground, loud noise, poor air purification, unable to solve the communications between surface and underground, we try to optimize and ameliorate the device combined with its original principles in this paper. Based on theoretical analysis, experimental study and CAD software, combined with ZigBee wireless communication protocol, we designed a new and advanced air self-rescue device, which containing LED warning lights, buzzer and high-reflective fluorescent material, achieving the functions of automated warning and starting, and underground communication network in urgency. The basic performance tests of the processed products show that the device parameters are suitable for human adaptability and can be used for underground emergency. The results provide a reasonable solution for workers to rescue themselves in emergency in underground mining.

Research on effective sampling time in direct measurement of gas content in Huaibei coal seams

Jiang-Hai-Na, CHENG Yuan-Ping, AN Feng-Hua

2013, 30(1):  143-148. 

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In this paper，based on the desorption performance of No.3 and No.7 outburst coal seams in Qinan Coal Mine，the physical simulation direct method was used to study the influence of sampling timeonthe calculation accuracy of lost gas in direct measurement method of gas content，and the lost gas content was calculated by adopting Barrer formula based on the desorption data．The results show that the error of the calculated and actual lost gas contents is direct proportion to the logarithm of reading time interval，and will decrease when the initial linear measuring points of gas desorption decreases．Thus，it is suggested to chose 4~10 initial linear measuring points of gas desorption．When controlling the ratio of the difference value of actual and calculated lost gas content and the measuring results of direct method into 10%，the effective sampling control time will show a linear relationship with the gas pressure，and with the increase of gas pressure，the sampling control time will be decreased．

Influencing factors of air curtain in cutting off roadway airflow

JIANG Zhong-An, LUO Ye, NIU Wei

2013, 30(1):  149-153. 

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 In this paper, in view of the characteristics of mine air curtain in cutting off roadway airflow and the requirement of structural design, the main influencing factors of air curtain in controlling airflow were obtained by theoretical analysis on the flow model of single-machine recycling-type air curtain. Furthermore, the experimental model of air curtain to cut off roadway airflow was established by using similar principles. The experiment results show that the optimum angle of air curtain and optimum width of air supply outlet in the roadway are 30° and 8 cm, respectively. Finally, numerical simulation by FLUENT was conducted to verify the correctness of experiment results. The results can provide reliable theoretical guide to the structural design of mine air curtain in cutting off roadway airflow.

Numerical simulation on fire prevention by infusing carbon dioxide into goaf

SHAO Hao, JIANG Shu-Guang, WU Zheng-Yan, ZHANG Wei-Qing, WANG Kai

2013, 30(1):  154-158. 

Asbtract ( 1989 )   PDF (635KB) ( 1891 )  

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To investigate the flow rules of carbon dioxide during the process of infusing carbon dioxide into the goaf, three-dimensional geometric model of goaf were established, and through numerical simulation, the flow characteristics of carbon dioxide in the goaf were further studied. The results show that the air leakage in the working face can be reduced by infusing inert gas into goaf, and the carbon dioxide can reduce more air leakage into goaf than that of nitrogen when the same amount of carbon or nitrogen has been infused into goaf. Meanwhile, the carbon dioxide infusion can lower the oxygen volume fraction in the entire goaf, while oxygen volume fraction in the goaf lowers strikingly only when nitrogen is infused into the goaf for deep distance. Thus, infusing carbon dioxide into goaf can reduce the air leakage into goaf, and lower oxygen volume fraction in goaf more effectively, that is, infusing carbon dioxide into goaf can produce much better effects of fire prevention than that of nitrogen.