| As resources continue to be exploited and utilized,extending to deep mining has become an inevitable choice.However,deep engineering disasters caused by deep mining occur frequently.Coal and gas outburst as one of the most serious disasters,It is difficult to grasp the mechanism of its occurrence,hard to predict and control,and the outstanding"threshold"cannot be to be quantified.The evolution of coal energy and the law of gas migration have a major impact on outbursts.Therefore,this paper uses the“MTS Tension,Compression,Bending and Torsion Experimental Equipment”from the School of Aeronautics and Astronautics of Chongqing University and the“THM-2Gas-containing Coal Thermal-fluid-solid Coupling Test System”from the State Key Laboratory of Coal Mine Disaster Dynamics and Control to study energy evolution and seepage in gas-containing coal,and make an elaborate analysis of coal energy evolution law,gas migration rule,coal and gas outburst mechanism.The research results show that:(1)The energy evolution of gas-containing coal is universal and independent of the stress path.As the stress increases,the energy increases in the form of a quadratic function.The energy evolution of coal has typical nonlinear characteristics.Among them,the total input energy density has the largest growth rate,followed by the elastic energy density,which is very close to the growth rate of the total input energy density,and the dissipation energy density has the smallest growth rate.(2)The stress path has a significant influence on permeability,and permeability decreases exponentially with the increase of stress.The unloading permeability of coal samples increases with the increase in the number of loading and unloading cycles.The in-situ stress mainly affects the difficulty and flow direction of gas migration in the coal seam by controlling the pore and fracture system of the coal body.The maximum supporting pressure point is the boundary point that controls the direction of gas migration.(3)According to the distribution characteristics of stope supporting pressure,the energy distribution can be divided into energy dissipation release area,energy increase area and energy stable storage area;in the process of coal mining,the supporting pressure in front of the coal wall is an important factor that causes energy accumulation.The increased stress area is the key area for preventing and controlling coal and rock mass dynamic disasters.The coal and gas outburst energy criterion based on the principle of energy conservation has a certain guiding role in engineering practice.(4)Based on the evolution of the permeability with the effective stress of the test results,the key structure of gas migration and disaster is established.The structure can be divided into 7 parts.In the case of structures IV,V,and VII with poor air permeability,structures I and VI induces instability and failure of structure II,causing structure III high-energy gas coal to overcome the resistance of structure II to protrude toward structure I.This structure directly highlights the mechanical mechanism of coal and gas outbursts.(5)From the characteristics of gas migration and key structure,coal and gas outburst factors can be defined as outburst basic factors,key factors and inducing factors.The basic factors degrade the strength of the coal body.The key factors make the coal and rock mass in a critical mechanical equilibrium state.And the inducing factors break this equilibrium state and induce outburst.(6)Based on the key structure of gas migration and disaster,the coal and gas outburst mechanics criterion was established.This criterion applied that coal and gas outburst is a mechanical process with multiple factors.When the judgment indexI_m≥1,the coal seam has the risk of outburst;when I_m＜1,it is not conducive to the occurrence of outburst. |
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