Post-peak progressive failure characteristics and nonlinear model of coal-rock combined body

Based on the axial crack strain,the post-peak pro-gressive failure characteristics of coal-rock combined body is analyzed using its uniaxial and tri-axial compression test data. On this basis,by dividing conceptually the coal-rock combined body in the post-peak stage into two parts, i. e. cracked body and basal body, the constitutive model of cracked body considering natural strain at the stage of post-peak crack coalescence is established,and then the elastic deformation of basal body is considered. Finally,the post-peak nonlinear stress-strain relationship of coal-rock com- bined body is obtained. The results show that the model can well reflect the post-peak strain softening and residual strength of coal-rock combined body. Then,the two parameters of the model are analyzed and it is found that the axial crack propagation strain extremum achieves the maximum value in uniaxial compression and is far less than the maxi- mum under confining pressure. The equivalent inelastic flexibility is negatively correlated with the axial crack propaga- tion strain extremum and approximately linearly correlated with the energy drop coefficient,indicating that the equiva- lent inelastic flexibility can indirectly evaluate the extent of post-peak brittleness of coal-rock combined body. Further- more,the influence of parameter equivalent inelastic flexibility on the post-failure behavior of coal-rock combined body is more obvious than that of parameter axial crack propagation strain extremum.