Physical Simulation Test Study Of Coal Mass Dynamic Response And Coal-gas Two-phase Flow Migration During Coal And Gas Outburst

The coal and gas outburst is a natural dynamic disaster that seriously threatens the safe production of coal mines in China.The occurrence time is within seconds to tens of seconds.A large number of gas-containing broken coal rocks are thrown into the mining space or roadway,underground mining workers are buried,and facilities and equipment are destroyed.Causing major casualties and property damage.In recent years,with the continuous increase of the mining depth,the ground stress and gas pressure of the coal seam have continuously increased,and the number of outbursts has become increasingly frequent.Because coal seam gas pressure provides the main source of power in the process of coal and gas outbursts,it plays a leading role in the process of outbursts.Therefore,studying the impact of gas pressure on coal and gas outburst will continue to be an important task for coal mine safety production for a considerable period of time.At present,based on the combined effect hypothesis,many scholars at home and abroad have carried out a large number of physical simulation experimental studies,which have deepened their understanding of the coal and gas outburst mechanism.However,different scholars have different understandings of the outburst mechanism,which leads to different emphases of the simulation test and the design principle of the test equipment used.The understanding of the outburst mechanism of coal and gas cannot be clearly unified.To this end,a multi-field coupled coal mine dynamic disaster large-scale physical simulation test system independently developed by Chongqing University is used to carry out a physical simulation test of coal and gas outburst under the condition of gas-solid coupling.During the test,the coal seam gas pressure,coal mass temperature,coal mass ground stress,outburst strength,and impact force of coal-gas two-phase flow in the roadway,video images,roadway temperature,pulverized coal transport speed,and pulverized coal sorting characteristics were studied.The following main conclusions were reached:(1)During the development of coal and gas outburst,the gas pressure,temperature,and geostress near the outburst orifice decreased rapidly.During the decline of gas pressure,the phenomenon of multiple rises occurred,showing obvious pulse characteristics.In the coal body closer to the outburst orifice,the faster the gas pressure and temperature of the coal mass decreases,the lower area of gas pressure appears as a circular arc with the outburst orifice as the center and expands deep into the coal seam.In the deep part of the coal body,which is far from the outburst orifice,the temperature drop is small.The geostress in the stress-relieving zone changed greatly,and the geostress in the stress-concentrating zone began to rise slowly after a significant change.(2)After the occurrence of coal and gas outburst,the maximum impact force of coal-gas two-phase flow during the movement in the roadway is located in the middle.The attenuation mode of the impact force in the roadway is attenuates along the roadway.The temperature in the roadway decreases the most at the section closest to the outburst orifice,and gradually decreases along the roadway.The coal-gas two-phase flow migration process has layered characteristics.Large particle size pulverized coal moves along the lower side of the roadway,and small particle size pulverized coal moves along the upper side of the roadway under gas,and the movement speed is relatively slow.There is a secondary acceleration process in the process of the pulverized coal transportation in the roadway.The outburst pulverized coal quality exhibits a wave-like distribution in the roadway.The proportion of pulverized coal with large particle size gradually increases along the roadway,while the proportion of pulverized coal with small particle size is just the opposite.(3)The coal seam gas pressure has a significant impact on coal and gas outburst:the larger the initial gas pressure of the coal seam,the wider the range of influence of the outburst process on the change of gas pressure and ground stress in the coal seam,and the greater the coal mass temperature drop.With the increase of the initial gas pressure,the impact force in the roadway appears more peak points,and the pulverized coal in the roadway has a higher initial velocity,and the relative protruding strength also increases accordingly.The more significant the crushing effect on the outbursting pulverized coal.(4)The energy dissipation problem of coal and gas outburst process is analyzed from the perspective of energy.The main energy source of the outburst process is the coal mass elastic strain energy and gas internal energy.The release of elastic strain energy involved in the outburst process mainly comes from the stress-concentrating zone.The release of gas internal energy mainly comes from the stress-relieving zone and the stress-concentrating zone.The calculation shows that the gas internal energy release during the outburst process is 16 times the elastic strain energy,indicating that the gas internal energy is dominant.According to the analysis of energy conversion during the coal and gas outburst process,it can be known that as the elastic strain energy release of the coal seam increases,the coal mass crushing work,migration work and outburst total energy dissipation show an exponential growth trend.With the increase of the internal energy release of gas in the coal seam,the work of coal crushing and outburst total energy dissipation show a logarithmic growth trend,while the migration work of coal mass has a linear growth trend.