Abstract: In the stability analysis of the surrounding rock after the excavation of a circular cavern,the mechanical mech anism of how to simultaneously consider the postpeak shear expansion effect of the surrounding rock and the damage evolution and their coupled influence is not clear.Based on the Mohr-Coulomb criterion,an elastic-plastic analytical model coupling shear expansion and damage is constructed,and the relationship between the shear expansion angle and plastic strain is estab lished through the plastic potential function,and then the damage evolution equation characterized by plastic volumetric strain is derived,so as to organically link the post-peak strain softening characteristics of the surrounding rock and the volumetric ex pansion induced by shear expansion and the damage development.In order to solve the nonlinear problem of the controlling e quations in the plastic zone,the finite difference method is adopted for the hierarchical solution,and a semi-numerical and semi-analytical iterative stress-strain-damage computation process is proposed,which can be solved to obtain the distributions of the stress,strain and damage variables of the surrounding rock.The results show that: the established coupling model has been verified by cases,and compared with the traditional linear softening method with strength parameters,this model describes the post-peak softening behavior based on the physical mechanism (volume expansion leads to damage),which is more general and reasonable;the increase of damage parameter β and shear expansion angle ψ will exacerbate the damage of the cave wall and lead to a significant increase in the range of the plastic zone and the loosening circle,but neither of them affects the maximum peripheral However,neither of them affects the maximum circumferential stress value of the surrounding rock;the damage pa rameter β has a significant effect on the rate of recovery of radial stress to the original rock stress level,and the larger β is,the slower the recovery is,and the effect of the shear expansion angle ψ on the recovery rate is negligible.The above quantitative and qualitative conclusions can provide important references for the assessment and control of underground engineering rock stability.

Key words: shear dilation effect,damage evolution,Mohr-Colomb criterion,circular cavern,loose circle