Journal of Mining and Safety Engineering

Research on Water-Resisting Property of Top Carbonatite Strata of Ordovician in Baiyunwusu Coal Mine and Its Application

BAI Hai-Bo, RONG Hu-Ren, LIU Shu-Cai, WEI Xiao-Qi, ZHANG Bo-Yang, JIAO Yang, CHEN Long

2012, 29(5): 601-606.

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In order to solve the problem of mining safety under water pressure of aquifer in lower coal group of Zhuozishan coalfield in Inner Mongolia, so based on years of research – “Top of Ordovician exists carbonate aquifuge in North China”, Baiyunwusu mine which is nearby Luotuoshan mine is chosen as the field test in-situ, to carry out the macro- and micro-researches on the floor of lower coal seam (16#) and test mining. The results show that: 1) There is a layer of carbonate aquifuge , with 150 m in thickness, existed in the top of Ordovician underlying coal seams floor, while the lithology is dark gray marl with less mudstone deposition. Meanwhile, the real section of the aquifer is appeared in caesious dolomitization of limestone under-laied the dark gray marl strata; 2) The vast majority of pore diameter of dark gray marl in Kelimoli group is less than 5 μm. Because of the poor pore connectivity, the effective pore is difficult to be formed and it is hard to seepage in nature; 3) The performance of the new tectonic movement is the resurrection of large old fault and generation of some small new fractures. Besides, the fractures provide the initial channel to Karst development and also constitute the main Karst water reservoir shift space and access; 4) The main threaten of Ordovician Karstic water to safety mining under water pressure of aquifer in Zhuozishan coalfield is hydraulic conductivity fracture, collapse column and other parts of the vertical channel, and the key area to control water inrush is Heilonggui thrust fault and F14 normal fault. Eventually, the safety mining in many workfaces in Baiyunwusu mine confirms that the top of Ordovician carbonatite strata is not only the aquifuge, but also the key aquifuge.

Prediction on the Height of Water-flowing Fractured Zone for Shallow Seam Covered with Thin Bedrock and Thick Windblown Sands

WANG Lian-Guo, WANG Zhan-Sheng, HUANG Ji-Hui, ZHOU Dong-Lei

2012, 29(5): 607-612.

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Shendong mining area, located in the arid and semi-arid areas, is an important coal origin in China, where the overburden structure has characteristics of shallow seam, thin bedrock and thick windblown sands, thus, the green mining (especially water preserving mining) has important significance in this area. Based on the failure characteristics of different rock strata, combining with the analysis of deformability, bearing capacity, and physical quantities associated with mining, a mechanical model predicting the height of water-flowing fractured zone(WFZ) is given, which is further used to analyze the height of WFZ in LW12610 of Daliuta coal mine. Both the results of numerical simulation and field observation show that the mechanical model is advisable.

Closing Mechanism of Mining-Induced Fracture in Coal Mine Aquifuge and Its Application

XU Zhi-Min, SUN Ya-Jun, DONG Qing-Hong, ZHU Zong-Kui

2012, 29(5): 613-618.

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The mining-induced fractures in roof and floor are the origin of a series of mine disasters. Thus, the research on the development and evolution law of the fractures has great significance to the mine disaster prevention. To study the closing mechanism of mining-induced fractures in overburden aquifuge and the associated influencing factors, several research means, including the ultrasonic imaging technology, mineral composition measurement and expansibility experiment are introduced in this paper. The results show that the expansion rate of the overburden aquifuge shows direct proportion to the montmorillonite content (including mixed minerals of Illite and montmorillonite) and its distance to the coal seam roof. Meanwhile, when the overburden structure is not suffered a severe damage, if the expansion rate is greater than the development rate of fracture, the mining-induced fracture can be closed effectively. Finally, the research result has been successfully verified by the penetrability evalution of coal mining under water body at Xin’an Coalfield and the water-preserved mining at Shendong Mining Area, and has achieved a good application effect in practice.

Research on the Process of Fracture Development in Overlying Rocks Under Coal Seams Group Mining in Wanli Mining Area

HUANG Han-Fu, YAN Zhi-Gang, YAO Bang-Hua, XU Hui-Jun

2012, 29(5): 619-624.

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Numerical model for coal seam group mining in Wanli mining area was built by using the software UDEC, the process of the fractures development and the interaction when mining between the coal seams group were numerically studied, the development rules of the failure of the overlying rock mass was analyzed and its predicting height of 3-1 coal seam determined. The numerical simulation results shows, 5-1 coal seam mining process caused the slightly increased of the overburden fracture height of 3-1 coal seam, and the height of water flowing fractured zone of 3-1 coal seam can reach 40 m. Moreover the height predicted by empirical formula is 41~50 m, and the height measured by transient electromagnetic and drilling is 45 m. Based on the development rules of the failure of the overlying rock mass, the mining area is divided into 5 kinds according to water-rich degree of aquifer and the thickness of water-resistant strata, namely, non water area, non water protection area, natural water protection area, water protection area and observation area. According to water protection area, we put forward a set of water protection techniques, which is applicable for mining practice.

In-situ Dynamic Observation and Numerical Analysis of Thick Coal Seam Floor’s Failure Law Under the Mining

ZHANG Rui, JIANG Zhen-Quan, YUE Zun-Cai, ZHAO Lian-Tao, YU Xu-Lei

2012, 29(5): 625-630.

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Based on the condition of fully-mechanized working face in one mine, by using the field strain measurement and numerical simulation as a mutual authentication method, a comprehensive comparative study of the thick seam floor’s failure depth under the mining was carried out in this paper. Field measurement studies show that the failure depth of the coal seam floor is about 13~16m. The influence of the mining pressure on the floor presents the feature of“advance”appearance and “lag” continuity, while the advance and lag distances are manifested as the feature of decreaing gradually from shallow to deep. The numerical simulations indicate that floor failure zone affected by mining is between 0~16 m under the coal seam, which means the greatest failure depth of floor is 16 m, the zone of 16~36 m under the coal seam is slightly affected by coal mining, and the mining pressure tends to in situ pressure along with the increase of depth. By the comprehensive analysis, the failure depth of coal seam floor is 16 m, and the research results can make reference for safety mining of coal resources and mine water disaster control under the similar conditions.

Failure Mechanism of Roadway Surrounding Rock in Deep Thick Coal Seam and Its Support Optimization

WANG Han-Peng, LI Shu-Cai, WANG Qi, LI Wei-Teng, LI Hai-Yan, LI Zhi

2012, 29(5): 631-636.

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To study the failure mechanism and support measures of roadway surrounding rock in deep thick coal seam, based on geological conditions analysis, the borehole TV and geological radar were used to survey the failure modes and rules of roadway surrounding rock in this paper, and the failure mechanism of surrounding rock was obtained through numerical simulation. On this basis, the targeted optimization support program and specific parameters of pretension bolt network coupled with yieldable cable beams were proposed. The results show that the failure degree decreases successively from the surface of surrounding rock to the interior, and forms 3 to 4 failure zones, while the external two failure zones are the traditional relaxation zones. The relaxation zone distributes in coal seam and bottom mud, while the average thickness of relaxation zone in the top is 3m, and is easy to cause separation. The roadway is more unstable in thick coal seam, while the failure mechanism is that the roof bolts locates in the relaxation zone of thick seam, and easily produces slippage of anchor end and overall falling. In-site support test shows that the proposed optimization support program is effective to control the stability of thick coal seam roadway.

Instability Characteristics and Support Analysis on Surrounding Rock of Soft Rock Gateway in High-Pitched Seam

XIN Ya-Jun, GOU Pan-Feng, YUAN Dong-Feng, LIU Hua-Yun

2012, 29(5): 637-643.

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In this paper, through the theoretical analysis of instability characteristics of soft rock gateway in high pitched seam, the structured instability equation of the gateway is established, and the coupling support scheme is proposed according to the coupling support idea. Additionally, the comprehensive analysis of the coupling support scheme is further carried out by numerical calculation, similar simulation experiment and practical supporting test. The results show that the instability of gateway roof has an arc asymmetry breaking, while the instability of two sides mainly shows shear slip of the triangle breaking bodies. The serious breaking lies in the upper of side angle, and the breaking in the middle-upper of roof is the inducing point of surrounding instability. Thus, the stability of surrounding rock is related to coal seam angle, shear surface length, and physic-mechanical parameters of coal-rock mass. After gateway supporting, the plastic breaking zone of surrounding rock along the inclination of coal seam is less, and the amount of roof separation is kept in reasonable range. Moreover, the improvement of two-side supporting strength is beneficial to the stability of gateway surrounding rock.

Study on Influence of Temperature on Anchorage Performance of Resin Anchored Bolt

HU Bin, KANG Hong-Pu, LIN Jian, CAI Jia-Fang

2012, 29(5): 644-649.

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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.

Numerical Simulation of Cross-Section Shape Optimization Design of Deep Soft Rock Roadway Under High Stress

MENG Qing-Bin, HAN Li-Jun, QIAO Wei-Guo, LIN Deng-Ge, WEI Lie-Chang

2012, 29(5): 650-656.

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In this paper, roadways with different cross-section shapes, including rectangular, trapezoidal, straight wall arch, horseshoe-shaped, oval and round shape, are selected to be optimized. Based on FLAC3D simulation, the surrounding rock deformation characteristics and rock plastic zone distribution are studied after the excavation of six kinds of typical roadway, and the influence of different side pressure coefficient to them is also analyzed. The numerical simulation results show that the cross-section shape has large effect on the deformation characteristics and plastic zone distribution of surrounding rock. According to the size of side pressure coefficient and direction of principal stress, the round and oval shapes are the optimal cross-section shapes of deep roadway under high ground stress. Thus, selecting the roadways with round and oval shapes, can improve the stress state of surrounding rock, reduce the deformation amount and damage range of plastic zone in surrounding rock, which is beneficial to the long-term stability of deep soft rock roadway under high stress.

Research on Response Characteristics of Bolt Pretension on Supporting Effect of Rock Roadway in Coal Mine

CHANG Ju-Cai, XIE Guang-Xiang

2012, 29(5): 657-661.

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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.

Experimental Study on Linkage Anchorage Technique of the Pre-Stressed Anchors

LONG Jing-Kui, ZU Zi-Yin, WANG Yong-Song, LUO Wei-Dong

2012, 29(5): 662-667.

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To enhance the strength, stiffness, and anti-deformation ability of anchored mass in surrounding rock, a design concept of “hard preload, high strength, high stiffness, high anchored stress and low density” is introduced based on the anchorage mechanism of anchors. In the on-site experiment, high strength anchor bolts and the components are used as the anchorage materials, and linkage components are adopted for the sake of crosswise and longitudinal linkages of the anchor bolt group. Then, active anchorage effects are achieved by raising anchored stress and hard preload of the anchor bolt group. In this way, the anchor bolts and anchored mass constitute a bearing structure, which can decrease the deformation and damage of the surrounding rocks, and improve the safety situation of roadway. The experiment results show that this design concept and its application can well solve such problems as breaking joint development, uneven deformation of roadway roof and low speed excavation. Marked by its validity, applicability and potential economic interests, this design concept is worth applying and promoting.

Research on Surrounding Rock Stability of Soft Rock Tunnel and its Construction Method

DENG Hua-Feng, LI Jian-Lin, WANG Le-Hua, ZHU Min, DENG Cheng-Jin

2012, 29(5): 668-673.

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When digging large-span long-diversion tunnel in soft rock, because of the poor stability of surrounding rock, one of the pivotal questions is to ensure the stability of the surrounding rock and safe construction. In this paper, a 3D model of the diversion tunnel is established based on engineering exploration and analysis of environmental geological conditions. Then, the surrounding rock stability after excavating is analyzed based on unloading rock mass mechanical theory and method. After taking the effects of dynamic unloading into consideration, the calculation results show that large deformation occurs in surrounding rock, which mainly locates in the partial regions near the confluence of faults and tunnel, while the arch subsidence of other cavity axis section is about 10mm, the relative displacements around the tunnel are within the specification tolerance, and the abutment tunnel is stable during and after excavation processes. The influences of unloading effect, such as obvious plastic zones, local deformation and stress concentration, are especially remarkable in faults and unconformity contact planes, which should be caused enough attention, that is, it is necessary to take supporting measures in time or take advanced support during excavation processes. Finally, some feasible suggestions about the construction method are put forward according to the calculation results. The research results can offer important support for the design and construction of diversion tunnel.

Feasibility Study on combined development for mining converted from underground to surface

WANG Hai-Jun, LI Ke-Min, HONG Yong

2012, 29(5): 674-678.

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According to the characteristics of mining converted from underground to surface, we studied the open-pit and underground developments in one mine, and put forward two combined developing forms in the mine with its mining converted from surface to underground, including the end slope combined developing and pit bottom combined developing. Additionally, combined with the actual mine production geology conditions, we demonstrated the expansion feasibility of the mine, and used relative payback period to evaluate the economic efficiencies of different developing forms from the aspects of investment and production costs, then selected out the combined developing method which is suitable for the mine converted from surface to underground mining. The results show that the end slope combined developing is accord with the production practice of the mine, which can not only make full use of the exiting production and transportation systems of the underground mine, reduce the construction investment, and accelerate the construction speed of open pit, but also can expand the mining scale and improve the economic benefits of mineral resource development. Thus, this developing form can provide support for the construction of high yield and high efficient mines, and has practical significance for the mines converted from underground to open-pit mining in the development process of China's coal resources.

Deformation Calculation in Soil and Rock Mass of Slope in Open-pit Mining and Its Safety Evaluation

GUO Qi-Lin, QIAO Shi-Fan, WANG Lu

2012, 29(5): 679-684.

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Open-pit mining may result in many excavating slopes. In this paper, to evaluate the safety of excavating slope, based on the stochastic medium theory, we deduced the formulae for calculating movement and deformation of rock and soil mass induced by slope excavation, proposed the deformation failure criterion of stochastic medium and the criterion for estimating the safety of surroundings. Meanwhile, in view of the non-integrability of the formulae, the computing method for the formulae is further studied, that is, the slice method is used to get the semi-analytical solution to predict the deformation of rock and soil mass. Through an engineering example, the criterion can be well used to predict movement and deformation of the rock and soil mass induced by open-pit mining, and to evaluate the slope safety easily, which can provide reference for the treatment measure design of slope.

Probability Analysis of Microseismic Activity in Underground Mining

MIAO Hua-Xiang, JIANG Fu-Xing, SONG Xue-Juan, YANG Shu-Hua, WEI Quan-De

2012, 29(5): 685-693.

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To characterize the stochastic features of microseismic activities in coal mining, three statistical variables, including distribution rate of microseismic energy, occurrence rate of microseismic events, and spatial distribution of events, were proposed in this paper. In addition, the methods to analyze probabilities of these variables were also established based on the probability theory and mathematical statistical principle. The calculation results of the field microseismic data in one mine show thatthe probability density of microseismic energy presents the normal distribution;, the probability density of microseismic occurrence is similar to Poso distribution, while the probability density of microseismic spatial distribution presents multi-patterns. Meanwhile, although no certain patter is revealed from the spatial distribution, most microseismic events are occurred in the front and two sides of the working face, as well as the top and bottom of the coal seam, which means the occurrence probability of microseismic events is higher in the mutation location of rock mass characteristics. The field application proves that these three statistical variables and the corresponding probability density distributions can be well used to characterize the microseismic activities in time, spatial and energy, which may significantly improve the fundamental research in microseismic monitoring and its application in coal mining.

Mechanism Research on the Spall Fracture Phenomenon in Outburst and Coal Bump

JIN Hong-Wei, HU Qian-Ting, LIU Yan-Bao, WANG Bo

2012, 29(5): 694-699.

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Because of the frequent occurrence of suddenly unload of rock stress in outburst or coal bump, this mechanical condition was used to established a simplified spall fracture model. The stress propagation in rock mass after the suddenly unload of rock stress was analyzed based on kinetic theory, the cause of spall fracture was obtained, and the developing process of spall fracture was reproduced by numeric simulation. The result shows that the main cause of spall fracture in coal bump is the unloading wave which comes into being after the suddenly unload of rock stress, then part of the unloading wave is reflected during the propagation process into rock mass, the incoming wave and the reflecting wave interact to produce a tension region and thus lead to the tensile failure of rock. The cause of spall fracture in coal/gas outburst is affected not only by the interaction between incoming wave and reflection wave, but also by gas; gas influence manifest itself in two aspects, high pressure free gas is involved in the fracture propagation in coal, and the discontinuous releasing of gas pressure along with the discontinuous occurrence of spall fracture may induced inward propagating unloading wave again.

Model Test for Mining-Induced Movement Law of Rock and Soil Mass under Thick Unconsolidated Layers

LIU Yi-Xin, DAI Hua-Yang, JIANG Yao-Dong

2012, 29(5): 700-706.

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To reveal the movement characteristics of rock and soil mass due to underground mining under thick unconsolidated layers, which are different from those of normal condition mining, the simulated material model test was employed to simulate the rock and soil mass movement laws in this paper, and the model test data were then compared with field subsidence monitoring measurement. Thus, the mining-induced movement laws of rock and soil mass in mining areas with thick unconsolidated layers are obtained, and the particularity of subsidence laws for loose soil mass is pointed out, when compared with the laws of normal condition mining. Through the comparison with the subsidence values and mining degree of rock and soil mass, the controlling role of bedrock on surface subsidence is shown, then the difference of movement basins in bedrock surface and ground surface is described, and the movement mechanism of rock and soil mass is finally revealed. The results can provide reference for subsidence prediction, object prevention, safety and high efficiency mining in thick unconsolidated mining area.

Research on Deformation and Failure Regularity of Surrounding Rock of Gentle Dip Thin Iron Ore Body in Longwall Mining with Hydraulic Support

SONG Wei-Dong, ZHAO Shu-Guo, XU Wen-Bin, SONG Huan-Hu

2012, 29(5): 707-713.

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Based on the characteristics of gentle dip and thin iron ore body, the new method of longwall mining with hydraulic support is proposed to explore the ore body. In this paper, taking the ore body from -8’to -16’section between the Liangshui Well of Guandian iron mine and Dazhuang mine as the research object, the deformation and failure regularities of surrounding rock in stress, displacement and plastic zones were studied firstly by similar simulation experiment. Then, numerical simulation was applied to simulate the variation rules of surrounding rock in stress, displacement and plastic zones, and the results was also compared with the similar simulation experiments. The results show that the destruction of surrounding rock has obvious characteristics of intermittent and mutagenicity, and the fracture directions are parallel to each other. In the vertical direction, the fracture step of surrounding rock changes in different locations. Meanwhile, it shows evident shear action in the face end, and prominent tension action in the top of goaf. In addition, the surface subsidence near the working face is smaller, and shows parabola shape.

Estimation and Evaluation of Backfill Strength in Underground Stope Based on Multivariate Nonlinear Regression Analysis

HAN Bin, WANG Xian-Lai, XIAO Wei-Guo

2012, 29(5): 714-718.

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Backfill mix ratio changes greatly among different stopes during the test running of backfill system, thus, accurate control of the backfill strength of particular stopes plays an important role in the safety of mining in adjacent stopes, which is also a general technical problem. In this paper, L25 (56) orthogonal design was applied to conduct 25 laboratory mix tests in the backfill mix experiment, and the backfill strengths at different curing ages were tested. Meanwhile, EXCEL and SPSS were used together to present the regression equations of backfill strength and the slurry density, cement dosage, and ratio of artificial aggregate and tailings, respectively. Based on the statistics of 136 kinds of mix ratio, including the backfill strength test results in laboratory and the actual measured values in backfill application, the strength reduction factor of the two results was obtained. Based on the regression equations and strength reduction factor mentioned above, the backfill strength of more than 200 backfill mix ratio access were calculated under the test running period of backfill system. The analysis method introduced in this paper is applicable to calculate backfill strength with different mix ratio, and is highly adaptable and practical for similar mines.

Experimental and Numerial Investigation on Crack Expansion of Sandstone Containing Flaws

CHENG Long, YANG Sheng-Qi, LIU Xiang-Ru

2012, 29(5): 719-724.

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In this paper, to research the crack propagation and AE behavior of rock mass, an uniaxial compression text was conducted on the sandstone samples by using the servo-controlled testing machine and AE monitoring system. Meanwhile, a numerical simulation was carried out with the rock failure process analysis system, while the numerial results displayed a good consistency with the experimental results. On this basis, the influences of material heterogeneity on crack propagation were further studied by using multiple repeated simulation. The results show that the crack propagation of sandstone is greatly related to the heterogeneity of rock material. The main crack of the sandstone sample initiates from the end of pre-exiting crack firstly, and expands along the perpendicular of pre-exiting crack. Then the development of crack turned towards the loading direction，whereas, lately, the cracks on the samples grow in different directions whilst the length and speed of crack propagation are various at different stages. Moreover, the secondary crack parameters including secondary crack number, length, width and expanding direction are different.

Evaluation of Safety Quality Standardization in Coal Mine Based on Set Pair Analysis

LIU Shuang-Yue, WANG Juan, WANG Dan

2012, 29(5): 725-729.

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The coal mine scores are usually calculated to evaluate the safety quality standardization level in coal mine, while the scores are the comprehensive calculation of the scores of each professional aspect. This evaluation method which uses a single score to evaluate the security level of coal mine has the problems of failing to reflect the objective situation of coal mine authentically and concurrently, lacking of effectiveness in guiding the construction of safety standardization, and just chasing high marks in regardless of the importance of security precaution. Therefore, it is necessary to use SPA (Set Pair Analysis Theory) to conduct deep analysis of coal mine security. In this paper, based on the construction of the four level connection function of security standardization evaluation results, the average connection degree, set pair potential, pessimistic potential, and uncertainty of the coal mine are analyzed respectively. Thehe analysis can reflect the preferential order when t achieving the optimal security standardin coal mine, the gap compared to the standard, the trend and potential uncertainty of future transformation in the optimal security standard, et al, which will promotes the construction of safety quality standardization incoal mine more effectively.

Study on Safety Mining Method of Fully-Mechanized Top-Coal Caving in Coal Seam with Easy Spontaneous Combustion and High Coal Dust

WANG Yan, LIANG Bing, YUAN Xin-Peng

2012, 29(5): 730-734.

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Many problems, such as the difficulty of controlling top seam caving, the high dust concentration, the low top-coal recovery rate, may occur in the process of fully-mechanized top-coal caving in hard roof. To improve the cavability of the top-coal and control the spontaneous combustion, the presplitting blasting and controlling boreholes were arranged alternatively in the air-return roadway of coal face 111 in Tingnan coal mine, Changwu, Shaanxi, then the deep hole presplitting blasting combined with dynamic pressure water injection were carried out during the mining operation. Thus, the recovery rate of coal face was improved by 8.5%, the coal dust concentration decreased from 12.7 mg/m3 to 8.9 mg/m3. Meanwhile, through the injection of flame retardants in the controlling boreholes, the calorific value was decreased by 470 calorie per gram, the water content was increased by 2.56%, which effectively delayed the thermal process, improved the working environment, and ensured the safety mining of fully mechanized sublevel caving in the easy spontaneous combustion and high coal-dust coal seam.

Study on Permeability Charatieristics of Coal Body with Gas Pressure Variation

WANG Gang, CHENG Wei-Min, GUO Heng, LONG Qing-Ming

2012, 29(5): 735-739.

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To study the relationship between the permeability of coal body and gas pressure, we established the mathematical models of coal permeability and gas pressure variation based on the analysis of ,stress and strain of coal body absorbing gas, and carried out the experiments in the condition that the temperature is constant, radial strain is restrained strictly and moisture remains invariable. Using the methods which measuring the gas seepage discharges of coal samples with different adsorptive characteristics under different pore pressures and pressure drops to determine the permeability. The seepage discharge was measured by water drainage method combined with the gas micro-flow meter method, and the measurement results were analyzed comparatively with the curve of mathematical model. The results show that the permeability changes with the gas pressure, and the influence degree of gas pressure is different for different adsorption of coal samples. The change trends of the theoretical gas permeability of coal samples and the experimental values are basically accordance, while the maximal relative error between the theory and experiment values reaches to 8.62%. Therefore, the permeability under a certain gas pressure can be calculated according to the basic parameters and mathematical permeability model of coal samples.

Device Design and Experimental Study on High-Pressure Small Jet Punching Technology to Prevent Outburst

ZHANG Jia-Yong, LUO Xin-Rong, GUO Li-Wen

2012, 29(5): 740-745.

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In this paper, in view of the low power and high efficiency, the high-pressure small jet equipment and facilities suitable for putting in roadway were developed, including the hydraulic control system consisted of hydromotor, high-pressure oil tube and premissible motor, the remote monitoring system consisted of explosion-proof computer and camera apparatus, the punching system consisted of high-pressure water jet, gearing, high-pressure tube and water pump. Meanwhile, the tightness and pressure resistance of device were improved by the pressure and running test in laboratory. The field test results show that the high-pressure jet with a certain pressure and flow has the ability to break the coal body, and the punching gets deeply as the jet pressure increases. Moreover, under a certain pressure, increasing the flow is more favorable to improve the reaming effect, which makes more residual coal vent outside the borehole and improves the punching speed.

Research on Gas Diffusion Characteristic of Injected Water Coal

MOU Jun-Hui, CHENG Yuan-Ping, LIU Hui-Hui

2012, 29(5): 746-749.

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In this paper, to find out the mechanism of coal seam water injection to the gas diffusion, according to the exiting experimental conditions, the effect of moisture content of coal samples to the initial velocity of gas diffusion was taken as the breakthrough point for our research. Through the experiment, the initial velocities of gas diffusion of the coal samples with different metamorphic degrees in different moisture situations were studied. The experiment results show that the logarithmic relationship is existed bwtween the initial velocity of coal gas diffusion and the moisture content, and the initial velocity of gas diffusion is alleviated due to the water content in coal sample. In addition, the higher the metamorphic degree of coal sample is, the bigger influence of the moisture is. Moreover, it has the biggest influence when the moisture of coal sample is around 2%-7%, and when the moisture of coal sample is over 10%, the increasing of moisture content has smaller and smaller influence to the initial velocity of coal sample.

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