Mechanical Characteristic Analysis and Quality Evaluation of Rock Mass during Excavation and Unloading of Underground Powerhouse Chambers

There are different degrees of degradation in the excavation unloading,rebound of rock and rock quality around the underground chambers.Taking underground powerhouse chambers in Jinshajiang river for an project background,mechanical characteristic analysis and quality evaluation of rock mass during excavation and unloading are discussed based on the theory of unloading rock mass mechanics and finite difference method.The rock mass evaluation is finished by RMR method according to the mechanical parameters after rock excavation and unloading.The results show that with the excavation of chambers,the unloading area in surrounding rock is evolves constantly and the depth and range become larger and larger;after the excavation finished,there are different breakthrough areas in three main powerhouse chambers;the rock quality of unloading areas in surrounding rock is changed from class Ⅱ into class Ⅲ after excavation.