Abstract: The interlayer shearing and crushing fracture zone are the key factors affecting the stability of surrounding rock of underground caverns in interbedded layered rock mass. For the problem of the interlayer shearing and crushing failure of interbedded layered rock mass， the interface element model was introduced to simulate the interlayer contact characteristics. Based on this， the contact model algorithm was improved. In view of the possible contact states for nodes on the boundary of the contact surface such as bonding contact， slipping contact， opening and embedding contact， the corresponding contact state criterion and modified iterative algorithm were established， which can effectively simulate the nonlinear slip damage between layers of interbedded layered rock mass. Then， the proposed model was applied to the stability calculation of the surrounding rock of underground powerhouse of Azad Patan Hydropower Station in Pakistan. Compared with the calculation results of the transverse isotropic model， the stress and displacement at the interlayer transition zone vary discontinuously and increase after considering the contact; dislocation displacement occurs between layers， which is more obvious in the middle and lower parts of the side wall of the main underground caverns.

Key words: interbedded layered rock mass; underground cavern; interface element; shear slip; numerical simulation