Study On Energy Mechanism Of Rock Burst In Deep Coal Seam With High Gassy

With the gradual depletion of shallow coal resources,China’s coal production is moving towards a depth of more than 1000 meters.With the increase of mining depth,the in-situ stress and the gas pressure controlled by in-situ stress in coal and rock system increase sharply.Rockburst is a common dynamic disaster in coal mining operations.Its main manifestation is that the crushed rock mass suddenly breaks up and throws out into the open space or the whole coal seam extrudes,accompanied by violent sound and vibration.The frequency of rock burst hazards shows an obvious upward trend after mining operations enter the deep part,which seriously threatens the safe production of mines.Based on the energy mechanism of rock burst,through theoretical analysis,numerical simulation and experimental research,the mechanism of rock burst in deep high gas coal seam is studied in the following aspects:(1)Through theoretical analysis,the energy rebalancing process in the process of rock burst in coal-rock system is clarified.It is considered that the energy source of rock burst is the elastic potential energy stored in coal-rock mass and the expansion energy of gas in coal seam.After the occurrence of rock burst,these energy transfers become the energy that causes the breakage of coal and rock mass,the energy absorbed by the deformation process of coal mass,the energy of sound and photoelectricity,and the kinetic energy that causes the throwing out of broken coal and rock or the extrusion of coal seam.The main form of rock burst disaster is the kinetic energy resulting from the throwing out of crushed coal or the extrusion of coal seam.The energy surplus can be obtained through the study of other energy,which is the disaster-causing energy of rock burst.(2)After the excavation of underground space,the surrounding rock changes from elastic deformation to plastic deformation,which consumes energy while transferring the stored elastic potential energy.The energy consumed by coal and rock mass in different regions is different because of the different stress modes: the coal and rock mass close to the underground space is in a unidirectional stress state,and the energy consumed by failure is equal to the minimum energy required for failure under unidirectional stress condition;although plastic deformation also occurs in the deep surrounding rock,the existence of confining pressure makes different locations.The strength of coal is different,the energy consumed by plastic deformation is different,and the energy consumed can be calculated by plastic work.(3)FLAC3D numerical simulation software is used to study the change of energy field of surrounding rock in stope.The damage energy index of rock burst is used as the criterion to distinguish the change of energy field from fluid-solid interaction,and the role of gas in the occurrence of rock burst disaster is clearly and intuitively demonstrated.In the process of underground mining,the desorption of coal seam gas will result in the increase of elastic potential energy stored in the coal seam,which has greater damage energy index and increases the impact tendency of the coal seam.(4)In order to study the degree and mode of gas participation in the process of rock burst in deep high gas coal seam,a simulation experimental device for drilling in deep high gas coal seam was developed.The experimental device realizes three functions: high stress loading,high pressure gas input and simulated drilling operation.It can restore the change of stress field of coal body in deep high gas coal seam after disturbance of mining operation,and then analyze the change of energy field by calculation.(5)The experimental results show that the mining operation in the coal seam will cause the damage of the bearing structure of the coal body and transfer the stress to other areas.When the seal ability of coal and rock mass system is destroyed,free gas will emit outward,resulting in the decrease of gas pressure,and release the stored gas expansion energy in the process.The release of gas expansion energy results in greater roof and floor pressure acting directly on the coal body,which increases the elastic potential energy stored in the coal body,which is also the main form of gas participation in the occurrence of rock burst.The variation of elastic potential energy of coal caused by the release of gas expansion energy is significantly correlated with the pressure difference before and after gas emission,and also with the different adsorption characteristics of coal for different kinds of gases.(6)The distribution law of gas pressure in coal seam and the stress distribution law of surrounding rock in stope are obtained through formula deduction.It is considered that the coal seam near the end of goaf is in the superposition state of high in-situ stress and low gas pressure.The energy release caused by high elastic potential energy and gas desorption is superimposed here,which becomes the key area of energy source of rock burst disaster.The failure of coal mass in this area can be regarded as the beginning of rock burst.Energy accumulation,dissipation and release are dynamic equilibrium processes.If the aggregation rate is less than the dissipation and release rate,the coal-rock system is in a stable state.If the energy aggregation rate is greater than the dissipation and release rate,the system will gradually develop,and finally the rock burst will occur.