As the excavation of auxiliary opening L3 at the right bank of underground cavern in Wudongde hydropower station was carried out, the excavation disturbance led to rapid growth of surrounding rock deformation and surface rupture along interlayers of rock mass. The characteristics of deformation and failure of surrounding rock was preliminarily described based on the geological conditions, monitoring and geophysical prospecting data, and construction process. On the basis, deformation and cracking mechanism of surrounding rock mass was discussed by combining the surrounding rock mass structure characteristics, geostress and construction process as well as the three dimensional distinct element method. The results were as follows: (1) The steeply dipped rock strata was basic condition which caused rapid and continuous growth of surrounding rock deformation at upstream side wall of 7#～8# unit since the excavation of auxiliary opening L3. (2) The upstream side wall was exposed to considerable excavation disturbance effect due to the rapid construction of auxiliary opening L3. Then, the upstream side wall surrounding rock became a weak link and caused surface either open or slip. (3) The characteristics of deformation and failure of steeply dipped rock strata was very sensitive to excavation disturbance, which could be effectively reduced through reasonable control of the scale excavation and unloading disturbances. The results above could provide important reference for stability analysis and design support of similar steeply dipped rock strata of large span underground projects.
