Abstract: With the increase of excavation depth, the deep rock mass is in high stress and complicated geological environment and the zonal disintegration phenomenon is observed at some projects, which is largely different from failure modes of shallow caverns. Under the action of dynamic unloading, an elastoplastic damage softening dynamic model is put forward based on the strain gradient theory and damage softening model. The dynamical equation, the equilibrium equations, boundary conditions and the failure criterion are deduced by considering the strain gradient. The theoretical solutions of radial displacement, radial stresses and tangential stresses of deep surrounding rock mass at different unloading times are calculated by Runge-Kutta and Matlab. The total displacement and stress fields of surrounding rock are also obtained after excavation. The dynamic formation and development regularity of zonal disintegration in deep caverns are achieved. The radial displacement, radial stresses and tangential stresses of deep surrounding rock mass are exhibited as an oscillating mode. The number and the width of zonal disintegration are in good agreement with the data of model tests. The applicability of the elastoplastic damage softening dynamic model for zonal disintegration in the explanation of zonal disintegration is confirmed. This model can also be used to provide theoretical support for the deformation and failure of surrounding rock in deep underground engineering.

Key words: zonal disintegration in deep rock mass, dynamic unloading, strain gradient theory, elastoplastic damage softening dynamic model, variation law of oscillation, geomechanical model test