Journal of Mining and Safety Engineering

Stress distribution and damage law of mining floor

WANG Lian-guo, HAN Meng, WANG Zhan-sheng, OU Su-bei

2013, 30(3): 317-322.

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After coal seam mining, different abutment pressure zones are formed around goaf area, and the stress unloading and concentration can be passed to the deeper floors, then the destroy depth and scope of floors are also affected. In this paper, the half-infinite body model was established which comprehensively considered the stress characteristics in the strike and inclined directions of the working face, and the iterative formula of vertical stress in floors was calculated. Meanwhile, the stress distributions in floors with different depths were calculated by Software-MATHCAD. The results show that the stress contours in different floor strata present oval shapes, and the contour gradient in shallow strata is larger than that in deeper strata. Based on the stress analysis results and Mohr-Coulomb criteria, the maximum damaged depth in floor of one mine was calculated to 14.8 m, while the largest damaged depth of floor by field seismic monitoring was 15.2 m, which are identical with each other. The results in this paper can provide theory basis for surrounding rock controlling and safety mining above confined water.

Prevention measures for support crushing while mining out the upper coal pillar in close distance shallow seams

JU Jin-feng, XU Jia-lin

2013, 30(3): 323-330.

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Aiming at the universal support crushing disasters during mining out the upper coal pillars in close distance shallow seams, the prevention measures for the disaster were proposed on the basis of the inherent mechanism of the support crushing by theoretical analysis and simulation experiments. The results showed that, while mining out the upper coal pillar, the three hinged structure of the key blocks above the coal pillar was unstable, whose relative rotary movement would cause the key stratum structure between the two seams to lose its balance because of overload. Thus the support crushing accident in the mining face jammed. Therefore, the key to the disaster prevention was to regulate the key blocks’ rotary movement. Hereby, the disaster prevention measures of the support crushing were proposed by prompting the key blocks to rotate in advance, preventing and destroying their rotation. All the prevention measures were verified by the similar material simulation experiments with a notable field application effect.

Stability analysis on support in large inclined coalface during special mining period

ZHANG Dong-sheng, WU Xin, ZHANG Wei, FAN Gang-wei

2013, 30(3): 331-336.

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Fully-mechanized mining technology is difficult to apply in large inclined coal seams, due to the hard stability control of fully mechanized supports under such conditions. Based on the 3up509 large inclined and mining height coalface in Gaozhuang Coal Mine, the mechanical analysis of support stability (dumping and slipping) was done during special mining period (roof fall or passing through fault) from inclined and strike direction in this paper. The analysis results show that the minimum working resistance for keeping support stability in 3up509 coalface should be not less than 4 743 kN, and the support selection of 6 600 kN resistance is reasonable. In addition, based on the analysis of the mechanics, the technical measures of increasing setting load of support, adding bottom adjustable jack device in support base, installing anti-inclining device on the top beam of support and changing movement way of support have been proposed, which can effectively prevent supports to happen slipping and in- clining during coalface process, and greatly improve the overall stability of supports in coalface.

Key problems of safety mining in caving coal with weak thin bedrock

DU Feng, BAI Hai-bo, JIANG Guang-hui

2013, 30(3): 337-342.

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The two key issues concerning safety mining in caving coal with weak thin bedrock are the development law of mining-induced fissure and variation regulation of support load. This paper uses physics simulation, theoretical analysis and field measurement to further research the two problems centered on the fully-mechanized caving face in thin bedrock area of Zhuxianzhuang coal mine. The result shows that weak thin bedrock is rich in clay minerals. The bedrock is liable to disintegrate and expand because of weathering under the chronicle impact of groundwater, effectively resisting the development of mining-induced fissure. The fissure-mining ratio in the top coal caving ranges from 3.6 to 5.4. The crack developing height of the breakage is much less than the normal thickness of the bedrock, and the thinner the bedrock is, the more obviously resisted the height of the fractured zone is. The bedrock’s mechanical property will be greatly weakened under the weathering. Without basic roof bearing layer in the roof, the working resistance of support is much less than the rated working resistance. The roof weighting step is far less than that of normal bedrock, and therefore the phenomenon of weighting is not obvious.

Stability control of support – surrounding rock in the large inclination fully mechanized island face

XIE Sheng-rong, ZHANG Shou-bao, HE Fu-lian, XIAO Dian-cai, TIAN Chun-yang

2013, 30(3): 343-347.

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In allusion to the problem of support–surrounding rock accidents when No.1523 fully mechanized face with large inclination advanced to the island district, we analyzed the cause of the accident. The relative relationship between roof fall and rib spalling and support parameters was studied by spot testing and regression analysis. Then the synthetical control technology including fault diagnose, device for anti-falling and anti-slipping, stability control indices, equipment operation process and so on was put forward. Result shows that the frequency of roof fall height over 0.40 m decreased from 76% to 16%, and the frequency of rib spalling over 0.50 m decreased from 72% to 23% after the technology was applied in coal face of No.1523. So no serious accidents of rib spalling and roof fall occured, the control problem of support–surrounding rock instability in the coal face of large inclination and island district were solved.

Optimization analysis of span-depth ratio for roof safety control in gob-side entry retaining under large mining height

HAN Chang-liang, ZHANG Nong, QIAN De-yu, XUE Bo

2013, 30(3): 348-354.

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Considering such factors as mining pressure field, rock bearing capacity and support structure strength, the influence of span-height ratio for gob-side entry retaining on surrounding rock deformation was analyzed．Numerical simulation models were established for comparative analysis of nine schemes for gob-side entry retaining with different span-height ratio under large mining height, and the results showed that optimized section configuration can substantially improve the stability of and non-deformability of the surrounding rock structure. Plastic range and surrounding rock deformation both decrease with the reduction of roadway span when the roadway height has been determined．The surrounding rock deformation is more sensitive to the reduction of span when the roadway height exceeds 3 m, and the effect of optimization is more evident while the span-height ratio is less than 1.3．On this basis, the determination method and technology thoughts are proposed for optimal span-height ratio of gob-side entry retaining under large mining height, which has been successfully applied to the field test in 4.2 m large mining height face with the roadway height of 3.8 m and span-depth ratio at 0.79．

Instability mechanisms and dynamic superposition coupling support in extremely fractured and soft rock roadway

ZONG Yi-jiang, HAN Li-jun, MENG Qing-bin, GAO Jian-ming

2013, 30(3): 355-362.

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Based on long-term mine pressure monitoring, mechanical properties test results, mineral composition analysis and broken zone detection results of surrounding rock in Zhaozhuang mine, the deformation and failure characteristics of surrounding rock were analyzed, and the instability mechanisms were also revealed. The dynamic superposition coupling support technology composed of reserving deformation, bolt-net-anchor-spout coupling support and bolt-grouting support was proposed for the extremely fractured and soft roadway. The effects of dynamic superposition coupling support technology were verified by similar model test and engineering practice. The study shows that the deformation of the surrounding rock can be effectively controlled by means of releasing deformation energy and high stress in surrounding rock through reserving deformation, high prestressed cables in the roof, high prestressed bolts and low prestressed cables in the sides to achieve the goal of pressure relief and roof control, the combination of low pressure filling and high pressure permeation grouting to form the positive and effective bolt-grouting support and multilayer composite beams structure, and bolt-grouting support to control floor heave.

Deformation characteristics and controlling of tailgate in high stress high gas and outburst region of deep mine

CHEN Xiao-xiang, GOU Pan-feng, FAN Zeng-zhe, LIU Jun

2013, 30(3): 363-368.

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Concerning the intense distortion of surrounding rocks in Shoushan No.1 mine in excavation process, field investigation, coal and rock test, theoretical analysis, underground test and measurement were conducted. After analyzing deformation failure characteristics and support difficulties, the key technology of surrounding rock controlling of this type was proposed. Results indicated that rapid rate, serious floor heave, large accumulative amount are the main features of tailgate deformation. The system of high pre-stress and high strength bolt supporting, the technology of synchronous bearing of bolt and anchor, appropriate resisting and concession technology, reserved section technology, supporting and reinforcing technology of key parts are adopted to effectively control deformation. The industrial test showed that the roadway deformation of two sides was controlled within 180 mm, and roof within 170 mm, after support was provided. This proposed support technology can effectively control the surrounding rock deformation in deep roadway.

Supporting mechanism of “yielding-supporting” beside roadway maintained along the goaf under hard rocks

NING Jian-guo, MA Peng-fei, LIU Xue-sheng, ZHAO Jun, LIU Wen

2013, 30(3): 369-374.

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When using gob-side entry retaining on the condition of hard roof, roadside support deforms and destroys easily because the length of hanging roof is large, the roof hangs long, and the stress exerted on roadside support is large. Mechanical model for gob-side entry on the condition of hard roof was built, and stress distribution of roadside support and deformation of surrounding rocks during different movement stages were simulated. Results show that in the early movement stage, in order to release some roof stress, roadside support should have larger yieldable capacity which allows roof to have certain subsidence under the premise that the support is not destroyed severely. In the later movement stage, roadside support should have greater strength to resist the weight of hard roof and cut roof. Based on this mechanism, unequal strength support body which is combined by soft material on the top and hard material in the bottom is put forward, and the field practice demonstrates that gob-side entry retaining technology on the condition of hard roof can be better achieved by using unequal strength support body.

Experimental study and application on non-destructive testing of bolt axial force in coal mine

XUE Dao-cheng, WU Yu, ZHANG Kai

2013, 30(3): 375-379.

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Bolt axial force is an important indicator of its working state in coal mine tunnel. The current detection means can not able to carry out random, rapid, non-destructive testing technology. In this paper, the relationship between horizontal natural frequency of anchoring system and bolt axial force has been established based on the principles of structural dynamics. By means of the dedicated electro-hydraulic servo system of bolt tensile testing, the influence of bolt diameter, anchoring state and surrounding rock conditions on the lateral vibration frequency of anchoring system and bolt axial force has been measured. The results show that the lateral vibration frequency of bolt anchoring system and bolt axial force have a good correlation, and the surrounding rock condition is one of the main factors affecting the lateral vibration frequency. The relationship between lateral vibration frequency and bolt axial force can be described by logarithmic function. Base on research founds, the nondestructive testing technology of bolt axial force has been developed. The field application shows that the technology can randomly, non-destructively detect the axial force of bolt in the tunnel.

An analysis of forming mechanism of collapsing ground fissure caused by mining

LIU Hui, HE Chun-gui, DENG Ka-zhong, BIAN Zheng-fu, FAN Hong-dong, LEI Shao-gang, ZHANG An-bing

2013, 30(3): 380-384.

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In order to study the relationship between collapsing ground fissures and geological mining conditions, the forming mechanism of collapsing ground fissures caused by mining in shallow-buried coal seam was analyzed through classified statistics, by adopting the theory of the main roof’s “O-X” type breaking principle and the key stratum theory of ground control. The dynamic development law of collapsing ground fissures was also studied. The engineering example conducted confirmed the reliability of the model. The research showed that when the mining-thickness ratio is less than 30，the fracture zone reach the ground, and the ground cracks easily. If there was no key stratum above the main roof, collapsing ground fissures developed with the breaking of the main roof, the shape of which was similar to the “O” type circle of the main roof. If there was a key stratum, the collapsing ground fissures would lag behind the mining schedule due to the breaking angle of rocks, which meant that there was a log angle of collapsing ground fissures，and the larger the distance between the key stratum and the main roof exists, the greater lag angle was.

Research on intelligent optimization for predicting parameters of probability-integral method

BIAN He-fang, YANG Hua-chao, ZHANG Shu-bi

2013, 30(3): 385-389.

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In order to effectively determine the prediction parameters of probability-integral method and to improve the prediction accuracy, a new method by combining Particle Swarm Optimization (PSO) algorithm and BP neural network (PSO-BP) was presented. In this method, an improved hybrid PSO algorithm was used to optimize the connection weights and thresholds values of BP neural network. An optimization model for prediction parameters of probability-integral method using this hybrid PSO-BP neural network algorithm was constructed based on analyzing the relationship between the parameters and geological mining conditions. Typical data of surface moving observation stations was used as learning and test samples. Analysis was made by comparing calculated values, observed values, and values of improved BP neural network. Results indicate that PSO-BP calculation model has higher convergence speed and higher precision.

Subsidence monitoring caused by repeated excavation with time-series DInSAR

LIU Zhen-guo, BIAN Zheng-fu, LV Fu-xiang , DONG Bao-quan

2013, 30(3): 390-395.

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The high resolution TerraSAR-X SAR data was used to monitor ground subsidence caused by underground coal mining activities with time-series DInSAR method. Analysis was made based on the detailed stoping records of the related working face. With the identified bounds of subsidence, some angular parameters, such as advanced influence angle, angle of subsidence and moving distance were derived. These parameters could be used to depict the evolution of ground subsidence caused by repeated coal excavation, which is quite different compared with subsidence caused by the first mining. In the end, terrestrial GPS surveying results, which were carried out at the same date when SAR image was acquired, were used to evaluate the DInSAR technology. The results confirm the reliability and validity of X-band SAR data in terms of subsidence boundary extraction and related angular parameters derivation, thus promoting the quantitative application of DInSAR technology.

Surface deformation law caused by filling mining under high tectonic stress

JIANG Wen-wu, XU Guo-yuan, LI Guo-jian

2013, 30(3): 396-400.

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In this paper, to reveal the surface deformation law and internal mechanism induced by filling mining under the complex environment of high tectonic stress, taking Jinchuan No.2 Mine as the engineering background, we put emphasis on the space-time evolution process of the surface deformation and subsidence in No.2 Mine, by using numerical calculation, site monitoring and theoretical analysis. The results show that the vertical deformation of the ground surface in filling mining under high tectonic stress experiences the stages of embryonic, differentiation and development. The ground surface gradually evolves into a subsidence deformation zone and a rise deformation zone from the whole subsidence deformation in the beginning. In addition, the subsequent orebody recovery will further promote the development of surface displacement rising zone, but the subsidence deformation gradually becomes stable, which has essential difference to that of the mines in gravity stress environment. More-over, the joint action of horizontal tectonic stress, mechanical property of surrounding rock and filling bodies are the inner motivation to the ground surface rising.

Energy dissipation analysis of stone specimens in SHPB tensile test

PING Qi, MA Qin-yong, YUAN Pu

2013, 30(3): 401-407.

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Variable cross-section split Hopkinson pressure bar (SHPB) with a diameter of 50 mm is adopted to implement radial loading to the mine sandstone Brazilian disc, which has a thickness-diameter ratio of 0.5. Dynamic tensile tests at various loading rates are obtained by altering impact loading pressures. Through investigating energy composition and dissipation characteristics of sandstone specimens during the dynamic tensile failure process, this paper tries to analyze the failure forms, average strain rate effect and dynamic tensile strength from energy dissipation perspective. It is found that energy absorbed by specimen mostly dissipates in the damage evolution and deformation failure process, which corresponds well to the tensile performance of sandstone under dynamic loads. The results showed that tensile strength and absorbed energy increase logarithmically with the average strain rate, a remarkable strain rate correlation. The results can provide some reference for dynamic tensile performance research of rocklike brittle materials.

Controlling effect of ground stress on gas pressure and outburst disaster

CHENG Yuan-ping, ZHANG Xiao-lei, WANG Liang

2013, 30(3): 408-414.

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To investigate the controlling effect of ground stress on gas pressure and outburst disaster, based on theoretical analysis and field verification, the evolution law of ground stress and its controlling effect on the coal structure, gas pressure and outburst disasters was analyzed in this paper. The results show that the evolution of tectonic stress plays a dominant role in the gas occurrence and migration. The coal seam gas pressure gradient under the higher tectonic stress may be greater than that under the hydrostatic pressure, which will lead to high gas pressure. In addition, the tectonic coal formed under the strong tectonic activity is charactered mainly by low strength, strong adsorption and diffusion. Moreover, due to the controlling effect on the coal structure and gas pressure, it is considered that the ground stress plays a leading controlling role in the outburst accident, which is the main driving force on coal mass destroy, and the premise condition for the existing of high-pressure gas. Finally, the leading controlling role of tectonic stress on outburst disaster have been verified by the characteristics of coal and gas outburst disasters in No.72 Coal Seam of Qinan Coal Mine.

Experimental study on pore structures of outburst coal and its adsorption characteristics at typical mining fields in Guizhou Province

LI Xi-jian, LIN Bai-quan, SHI Tian-hu

2013, 30(3): 415-420.

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In order to improve the understandings of pore structures and adsorption properties of outburst coal mined at typical mining fields in Guizhou Province, such structures and properties are tested by using related apparatuses based on their importance on the extraction of coal gas (coalbed methane) and the prevention coal and gas outburst of happening. Results show that a number of crystal materials and micropores exist on the surface of coal samples’ parallel beddings; one or several fractures in parallel or intersected with different sizes can be observed on the surface of samples’ vertical joints. The distribution of diameters of sample’s pores or fractures is mostly from 0 to 10 nm, and micropores with a diameter of 3 nm to 5 nm are the most abundant in coal samples, which are also the main spaces to adsorb the coal gas. When the relative pressure reaches about 0.8, the gas adsorption volume would increase greatly. The gas adsorption volumes change for different samples, generally, the bigger pore volume has more adsorption volume.

Balance time and accuracy advantage of spherical flow field in gas pressure measurement by passive method

LI Xiao-wei, JIANG Cheng-lin, CHEN Yu-jia, TANG Jun

2013, 30(3): 421-425.

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In this paper, the balance time and accuracy of passive method in gas pressure measurement was studied, the research shows that as long as there exits gas exchange face in the measurement process of passive method, the gas pressure can be measured. Meanwhile, through the calculation of established model, it is found that the pressure-relief diameter of spherical drilling hole is much smaller than that of the radial drilling hole in the formation process of drilling hole, thus, the gas loss is less. According to the limit equilibrium theory, the theoretical balance time is short, and the measured pressure value is slightly higher, that is, the accuracy is high. The calculation validity was verified by numerical simulation. The simulation results also show that as the free emission time increases, the spherical drilling hole takes a smaller percentage of the balance time of radial drilling hole, and the advantage of the balance time is more obvious. The field practice proves that the spherical drilling hole has obvious advantage in the balance time and accuracy during the gas pressure measurement process by passive method.

Reliability research of protective layer mining and pressure-relief gas drainage

LIU Yan-wei, LI Guo-fu

2013, 30(3): 426-431.

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Reliability theory was introduced into the protected layer mining，by summarizing seven main influencing factors. Besides the corresponding evaluation index，target layer，criterion layer and sub-criterion layer of the reliability evaluation system were also established. Based on the basic theory of analytic hierarchy process (AHP)，the judgment matrix was built to calculate the importance weight of the index method. According to its importance degree，the influence of every index on the system reliability was divided into four levels. Finally，the field case was analyzed in view of the reliability evaluation，which could provide a reference for other project cases.

Control effect of structure environment to coal and gas outburst in Pingdingshan mining area

ZHANG Jian-guo

2013, 30(3): 432-436.

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The topography and geomorphology and tectonic evolution characteristics in Pingdingshan mining area were studied under plate tectonics and geo-dynamic division theory to obtain the formation mechanism and spatial distribution characteristic. The results showed that the Pingdingshan mining area is subjected to the south-to-north downthrust and collision by Qinling orogenic belt, and thus the depression belt formed, bordered by Jiaxian, Xiangjia and Luye normal faults. The middle uplift and N font geomorphology in Pingdingshan mining area have structure environment to cause mine dynamic disasters such as coal and gas outburst. The III level and IV level active faults divided by geo-dynamic division controlled the macro-distribution of coal and gas outburst, and the V level active faults determined the local distribution characteristics. The mine No.12 was divided into four tectonic divisions, which controlled coal and gas outburst occurrence.

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

2013, 30(3): 437-442.

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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.

Water injection impact on gas diffusion characteristic of coal mass

CHEN Xiang-jun, CHENG Yuan-ping, HE Tao, LI Xin

2013, 30(3): 443-448.

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To study the gas diffusion characteristic and dynamic parameters change after water injection in coal mass, the desorption process of different water injection rates in coal samples under 0.5MPa adsorption equilibrium pressure were experimented on the homemade high-pressure water injection mixing plant. The experimental results show that the relation curves between time and desorption quantities of coal samples with different water injection rates have similar shape of Langmuir’s adsorption isotherm. In addition, all the coal samples with different water injection rates have limitation desorption quantities, and the variation of limitation desorption quantity with moisture is belong to exponential function. When the moisture increases from 0.05% to 12.04%, the limitation gas desorption amount decreases from 7.3383 mL/g to 2.7749 mL/g. Moreover, under the same adsorption pressure, the greater the moisture rate is, the smaller the gas desorption velocity of 1st minute (V1) is, and the change of gas desorption velocity of 1st minute with moisture is belong to logarithmic function. After water injection, Biot’s criterion of mass transmission increases, and the diffusion coefficient and Fourier’s criterion of mass transmission reduce, that is, the water injection have changed the diffusion kinetic parameters of coal mass.

Stress distribution and movement law around drainage borehole when considering rheological property

HAO Fu-chang, ZHI Guang-hui, SUN Li-juan

2013, 30(3): 449-455.

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In this paper, to investigate the stress distribution and movement law around gas drainage boreholes, the mechanical properties of coal mass around boreholes were analyzed, a visco-elastic plastic model considering the plastic softening and dilatancy was established, and the expressions of coal stress, displacement, pore size variation and pressure-relief range were obtained. In addition, the stress distributions and pressure-relief effects around drainage boreholes in the hard and soft coal seams were comparatively analyzed, the pore size variation rules of boreholes were studied, and the reason about rapid decay of borehole drainage concentration in soft seam was explained. The results show that the coal mass around boleholes have the properties of plastic softening, dilatancy and rheological. The boreholes in soft coal seam can get better pressure-relief effect, the creep deformation is more severely, and the unstabe failure can occur in a short time, which will block the gas drainage channel, and result in rapid decline of gas drainage concentration. Meanwhile, the pore sizes of boreholes in hard coal seam are reduced somewhat, but still in stable state, and will not block the gas drainage channel. But, with the increase of ground pressure in deep minefield, the creep deformation will increase, and the unstabe failure may occur. The research results agree well with mining practice, which can provide theoretical guidance for the determination of gas drainage parameters.

Relieved gas drainage and comprehensive control in gob of Y-type coal face in the first coal seam mining of deep multi-seams

LU Ping, FANG Liang-cai, TONG Yun-fei, LI Gui-he, ZHANG Gen-fa, DENG Zhong

2013, 30(3): 456-462.

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In this paper, in view of the difficulties of relieved gas control in the first coal seam mining of the deep multiseams with high gas and low permeability, taking Coal Face 1111(1) in Zhuji Coal Mine as example, we provided and implemented the technique to strengthen the wall closeness of gob remained entry, and the gob relieved gas drainage technique in the gob remained entry of Y-type ventilation coal face, with the combination of gob gas delivery law in Y-type coal face and the advantage of accumulated relieved gas withtin the gob. In addition, combined with the gas drainage in the upper relieved coal seam by the surface well drilling, the safety and high efficiency mining in the first coal seamin of deep multiseams was realized. The results show that the maximal and average absolute gas emission quantity is 72.39 m3/min and 43.64 m3/min, respectively. When the air volume in the face is 2 290~2 700 m3/min, and the gas concentration in the return airflow is less than 0.6%, the average gas drainage volume is 34.27 m3/min, where the average gas drainage volume in buried pipes is about 21.94 m3/min, which is 64% of the total gas drainage volume. Moreover, the average gas drainage rate is about 78% during the mining process. The research achievement can provide the basis for gas drainage and control in the first coal seam mining of similar deep multiseams in the future.

Experimental and mechanism study on gas explosion flame suppressed by foam metal

SUN Jian-hua, QU Zheng, WEI Chun-rong, WANG Shu-tong, ZHANG Jin-peng

2013, 30(3): 463-467.

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In this paper, by using self-designed 30cm×30cm square piping experimental study on gas explosion, the new and effective gas explosive device was explored, and the barrier burst material suitable for use in coal mines was studied. In the tests, density of 0.3 g/cm3 foam iron-nickel metal materials were placed in the pipe, and the flame temperature data and flame size were considered together as the judgment of the target material on the explosive wave energy control. The experiment results show that 0.3g/cm3 bubble iron-nickel metal have the inhibitory effect of gas explosion flame wave and strong fire resistant capacity, and the maximum decay rate of gas explosion flame temperature in the pipe is between 7.1~70.7%. Studies have also found that the thickness, diameter and substrate material composition have certain influences on the inhibition effect of flame wave, and the porous foamed iron-nickel metal with high thickness, small aperture, and high nickel-containing compositions is favorable for the flame wave attenuation.

Simulation of high-density electrical method in detecting coal fires and its application

SHAO Zhen-lu, WANG De-ming, WANG Yan-ming

2013, 30(3): 468-474.

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In this paper, the geo-electricity model of coal fires were established, and the forward modelings of Wenner α, dipole-dipole, Wenner-Schlumberger, pole-pole and pole-dipole were carried out by using the finite difference method. After adding noise interference into the forward data, the inversion was implemented to get the sectional drawing of apparent resistivity by using Gauss-Newton iteration method. The inversion results show that all the burning center, burned cave and loose zone present abnormalities in the sectional drawings of apparent resistivity of the five array types, while Wenner-Schlumberger array has the best effect in distinguishing the burning center, and the Wenner α array has the best effect in distinguishing the burned cave and loose zone. Moreover, the two array types mentioned above were applied to carry out high-density electrical detection in one fire zone, and the burning center, burned cave and loose zone were distinguished accurately. The research results provide theoretical basis and reference for the accurate detection of coal fires.

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