| The coal and gas outburst is a very complex dynamic phenomenon in underground mining process of coal mine. As the increasement of mining depth, stress, gas content and gas pressure will increase and permeability of coal will become poor and poor, which will lead more coal and gas outburst disasters and the increasement of number of outburst mines. In order to effectively prevent and control the occurrence of this accident, major coal-producing countries around the world have invested a lot of manpower and material resources to study coal and gas outburst, which can provide theory and technical basis for the prediction and control of coal and gas outburst. Currently, the mechanism of coal and gas outburst and the mechanism of rock damage and development still remain in the hypothesis stage, it can only explain some phenomenon during and after the outburst. All the research results still haven’t formed a complete theoretical system. Because of destruction, emergent property and specificity of coal and gas outburst, the monitoring and acquisition of paremeters of coal and gas during outburst is very difficulty, even impossible, which hinder the further development of research work. The coal and gas outburst is researched systemly through big size coal and gas outburst similar simulation device designed by laboratory independently in this paper. And all kinds of physical parameter of coal and gas during outburst is tested. The spatio-temporal evolution law of coal mining dynamic stress of coal infront of mining face is researched through FLAC3 D numerical simulation software. The corrosion and loss of pore gas on coal is studied through scan electric mirror(SEM), low temperature liquid nitrogen adsorption and coal body adsorption-solutions sucking gas strain test system. The effect of stress and gas in the coal and gas outburst is analyzed through rock mechanical, fracture mechanical, damage mechanics and so on. Finally, the real outstanding case is analyzed through the conclusion conclude in this paper. This article made the following key results:(1) One set of "large size similar simulation device of coal and gas outburst" is designed and manufactured indenpendently according to summarize the advantages and disadvantages of current coal and gas outburst simulation device. One ton coal and rock model can be laied and 100 L gas can be injected in this device, which can simulate the outburst happended underground really. The outburst under different condition such as different forming pressure, different size, different stressdistributions, different gas, different pressure and different top-floor property can be simulated through this device.(2) Cola and gas outburst similar simulation test was carried out according to 2# coal sample in Dashucun coal mine and 2# coal sample in Zhenxignerkuang through "large size similar simulation device of coal and gas outburst". The results show that the weights of outburst coal and rock sample were 369.9Kg and 373.6Kg, and throwing distance were 41.4m and 49.5m when adsorption stability gas pressure were 0.3MPa and 0.6MPa separately. The higher adsorption gas pressure was, the farther throwing distance would be, and the higher the pure coal proportion would be among outburst coal and rock sample, which can verify that the adsorption gas was the main reason of coal shredding in the process of outburst. After the outburst, outburst coal samples show the center line axis of symmetry axis symmetrical fan-shaped distribution as the outburst port was circle center. In two tests, there are 4 and 6 fan among the outburst coal and rock. And the collapsing roof distributes between fan. It can be concluded that during the first and second tests, there were 4 and 6 times process of gas crushing coal process.(3) The velocity distribution law of outburst of coal and gas flow can be obtained by processing video data which was obtained from tests. Average speed of coal and gas flow at outburst hole is 54.55m/s, and speed is reduced to 21.43m/s gradually at the outburst in the range that distance from outburst hole is from 1m to 6m. The weight of outburst coal and rock concentrated in the near place and far place from the outburst hole when there was no obstacle in front of the outburst hole. And the weight of outburst coal and rock concentrated in the near place of obstacle when there was a obstacle in front of the outburst hole. After the outburst happened, the settlement of roof occurred. The distance is closer to the outburst hole, the settlement is more. The settlement of roof next to the wall with outburst hole is 17.2cm. The distance of roof is farther from the outburst hole, the settlement is less. The direct roof of outburst coal seam bended and showed a clear natural arch shape.(4) Stress evolution law of coal during the test with coal sample from Dashucun coal mine was simulated by Flack3 D. The results show that in the process of coal and gas outburst, the coal internal stress transfer along the trend and tendency of working face, stress value and the area of Stress concentration zone on both sides of the outburst hole increased and the trend that the stress of roof transferred to deep part of coal seam existed. The evolution characteristics of strain of coal seam during the outburst was calculated by1 2and combined with evolution characteristics of stress, the evolution characteristics of outburst energy was calculated. The results show that inⅠstage of outburst, 30.26 KJ elastic potential and 775.65 KJ internal energy of gas were consumed, throw work of coal is 594.815 KJ and crushing work of coal is 211.095 KJ. During the stage from I stage to the end stage of outburst, 15.1KJ elastic potential and 481 KJ internal energy of gas were consumed, throw work of coal is 409.8517 KJ and crushing work of coal is 86.24 KJ.(5) The effect of fault on the evolution law of 172103 work face in Dashucun coal mine was research through FLACK3 D numerical simulation software. The simulation results show that the stress of coal whose distance from work face is 3~5m arrived at maximum value 25.5MPa when there was no fault in front of the work face. And this value is 1.7 times of initial stress, but it reduced to the value of initial stress at the coal whose distance from work face is 8m. So stress of the coal in the range of 8m from the work face changed a lot. During stress transfer, the stress of this part of coal rises firstly and then was compressed under loading, peak stress transferred into deep part of coal along with the advancing of work face and the stress of this part of coal reduced and expand to mined out space. In the process of expanding, some coal seam was destroyed and some new fractures were developed. When fault existed in front of the work face, the maximum of peak stress is 28.5MPa, stress concentration factor is 1.9. The maximum of peak stress of coal in front of work face rose firstly and then reduced after the work face is near than 200 m from fault.(6)The reason of coal and gas outburst happened more times near the fault structure is analyzed by rock mechanics and elasticity. Fault structure has great influence on stress, peak stress increased 3MPa due to fault structure and stress concentration factor increases from 1.7 to 1.9, and stress increased in front of work face, the closer to fault, the more stress changes. Meanwhile, stress concentration existed in the coal and rock in the both sides of outburst hole. Near the fault structure, peak stress of coal increased due to superposition of ground stress and tectonic stress. Meanwhile, soft coal developed a lot, permeability of coal is bad, compressive strength and tensile strength is weak, large gas pressure gradient is easily produced between release area and work face. So the stability of this part of coal is not enough and coal and gas outburst is easily occurred by external disturbance.(7)The erosion mechanism of pore gas on coal was researched through strain experiment. The results show that the bigger the specific surface area was, the stronger the adsorption ability is and the larger expansion deformation is. The stronger the adsorption property of gas was, the more obvious the erosion effect of gas on coal was. Expansion energy produced on the surface of micro fracture and fracture of coal due to pore gas, which induced the force among coal particle to decrease. So the surface energy needed to destroy the coal reduced, which caused the reduction of coal strength. Then coal and gas outburst happened under tensile stress of gas.(8)According to research results of front parts of paper, the outburst case of Dashucun coal mine was analyzed. The pore structure of fractal dimension of 2# coal seam in Dashucun was analyzed through SEM(scanning electron microscope). The creep experiment under the condition of step loading was carried out and the deformation law of return airway was tested. The results show that the rheological property of 2# coal seam is strong. When the 1772205 roadway was drive under coal pillar, crustal stress, concentrated stress, tectonic stress and advance stress superposed here. Compared with the coal without coal pillar, the stress of this part coal was much bigger and exceeded the yield strength of coal. So the length of Ⅱstage of creep was shortened and creep arrived at Ⅲ stage. And the coal and gas outburst happened under external disturbance. |
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