Abstract：The excavation has induced a series of unloading deformations and failure phenomena of rock mass including loosening and shearing deformation of existing discontinuities，and outburst and flaky failure of intact rock. The attitudes of the new failure planes are nearly parallel to the excavation surface；and the planes mostly are distributed within the depth of 4–6 m. The unloading deformation and failure have led to a notable decrease of integrality of rock mass，however，the main courses of relaxation are completed in several months. Since the excavation unloading is actually an energy release course whether it is provoked by excavation of rock mass or natural cutting of rivers. There is a clear distribution regulation for the deformation and failure phenomena，so it is suitable for investigating the unloading zones by the energy analysis method. A strain energy method for unloading zonation is presented，and the application of Xiaowan Hydropower Station has confirmed its feasibility and efficiency.
