Dynamic damage law and failure modes of layered coal-rock mass under impact loading

Abstract Up to now, most of the structural dynamic analysis is based on the Lagrange system, while the Hamilton system is composed of the phase space composed of the generalized displacement and stress, showing a wonderful symmetry, which opens up a new way for the theoretical research and calculation of dynamics. The physical model of the layered combined coal-rock is constructed by dividing the ‘outburst center’ coal in front of the heading face into the combined layered structure. Based on Hamilton mechanics, the Hamilton canonical equation under symplectic geometry structure is established, combined with Hamilton variational principle and symplectic time subdomain method, the multi-layer symplectic element control equation of coal-rock is established, and the dynamic displacement and stress transfer characteristics at any time can be solved by iterative calculation. The action modes of axial torsional stress, radial principal stress and shear stress of layered coal- rock under impact loading are determined, and the weak layer and interlayer stress transfer dynamic response behavior of layered coal- rock under complex stress conditions are determined. The conclusions are as follows: ①Under static loading, the layered shear stress circle provides the initial condition of damage failure, impact loading acts as an exciting force to trigger the torsion effect, forming the ‘ X ’ -shaped shear line in the radial and axial directions of the interlayer interface, and the boundary produces the ‘ V ’ -shaped dynamic spalling surface. ②The short axis is damaged before the long axis, and the central node is the starting point of instability. The main cracks are formed along the long and short axis respectively, and finally the ‘ O- + ’ failure mode is formed, which verifies the prominent axial and radial spallation phenomenon. This method avoids the non-conservation of system energy caused by energy dissipation, and will become an effective method to study the dynamic mechanical properties and damage evolution path of coal-rock. It has guiding and reference significance for the theoretical research and prevention technology of coal and rock dynamic disasters.