Abstract: During the excavation of deep caverns, the strain energy accumulation and release of surrounding rock are the most important incentives to cause the catastrophe damage. Aiming at the excavation of circular tunnel, the energy transient adjustment process of surrounding rock under the different unloading ways of initial in-situ stress (static and dynamic unloading) is analysed and compared, and based on energy point of view the damage scale of surrounding rock is calculated. The results show that, energy transmits from far and near in the surrounding rock by the radial stress working under the unloading of initial in-situ stress, and causes the strain energy of the near parts of surrounding rock gathering, with the excavation of underground caverns and tunnels. The strain energy of the near parts of surrounding rock decreases firstly and then increases, this caused by the dynamic unloading of initial in-situ stress; firstly the rock releases its own strain energy by radial stress working on the adjacent rock mass near the excavation surface, with the continuous transmission of the unloading stress wave, its own strain energy gathers by the working of adjacent rock mass away from the excavation surface. Comparing with the static unloading of initial in-situ stress, the high strain energy accumulation degree caused by the dynamic unloading of initial in-situ stress leads the larger extent of damage zone.

Key words: quasi-static unloading, dynamic unloading, strain energy accumulation, damage