Dynamic Failure And Energy Dissipation Characteristics Of Coal-rock Under 3D Coupled Static-dynamic Loading

Coal-rock dynamic disasters in deep mines are usually induced by the combined action of a complex stress environment and dynamic disturbance.Therefore,typical dynamic disasters such as coal and gas outbursts and rockburst are essentially the dynamic instability and failure behavior of coal-rock mass under the coupling of dynamic and static combined loads.To explore the dynamic characteristics of coal-rock under dynamic and static combined loading,the improved Split Hopkinson compression bar(SHPB)test device is used to carry out three-dimensional dynamic and static combined loading tests on coal-rock under different axial pressure,different confining pressure and different impact rate;The stress-strain curve,peak stress,peak strain and dynamic deformation modulus of coal-rock under different working conditions are systematically analyzed;The brittle damage dynamic constitutive model is used to simulate the failure process of coal-rock.Combined with the energy dissipation mechanism,the energy dissipation characteristics in the dynamic failure process of coal-rock are analyzed,and the occurrence mechanism of coal-rock dynamic disasters is further explored.The main conclusions are as follows:(1)Through the 3D coupled static-dynamic loading test,the mechanical properties of coal-rock under the combined action of axial pressure,confining pressure,and dynamic load is explored.The test results show that with the increase of axial pressure,the peak stress and dynamic deformation modulus of coal-rock gradually decrease,and the deformation resistance of coal-rock becomes weaker.With the increase of confining pressure,the peak strain of the coal sample increases first and then decreases;When the confining pressure is equal to the axial pressure,the peak stress of the coal sample is the smallest compared with other working conditions,and it is most prone to instability and failure.With the increase of impact velocity,the peak stress,peak strain,and average strain rate of coal samples increase,and the strain rate effect are more obvious.(2)Based on the test results,the relevant parameters of the brittle damage constitutive model are modified,and the SHPB test simulation of coal-rock under the combined action of axial pressure,confining pressure,and dynamic load is realized.The modified model can well describe the impact failure behavior of coal-rock under3 D coupled static-dynamic loading;The numerical simulation results show that both axial pressure and impact rate can aggravate the damage degree of coal-rock,while the confining pressure limits the crack propagation of coal-rock after impact load;The numerical simulation results can provide theoretical reference for coal-rock mining under different stress conditions.(3)The failure process of coal-rock is analyzed from the perspective of energy dissipation.When the reflection energy changes greatly,the transmission energy shows the opposite trend;With the increase of axial pressure,the energy dissipation mass density of coal-rock decreases gradually;With the increase of confining pressure,there is a critical confining pressure value(5MPa),which makes the mass density of energy dissipation increase first and then decrease;The increase of impact rate brings greater incident energy and dissipation energy to coal-rock,and the greater the damage degree of coal-rock.