Abstract: Based on improved PFC-FLAC numerical simulation method, this paper presents an improved particle flow acoustic emission (AE) model based on bilinear interpolation of nodal velocity in coupled region of FLAC model, and a method for judging the depth of rock mass failure zone according to the AE intensity. Both methods have been applied to studying the meso-mechanism of local rock damage and destructive characteristics for excavation surface of underground powerhouse cavern and contact surfaces of rock-anchored crane beams. The results show that the contact force chain of the shallow surrounding rocks is gradually sparse, and a large number of micro-cracks develop and merge into macro-cracks, and finally a shallow fracture zone appears, showing tensile fracture; with the increase of distance from the excavation surface, the surrounding rocks are damaged due to the large force at the early stage of excavation, and only a few micro-cracks are generated at the later stage, which correspond to the depth of rebound unloading zone. When the surrounding rocks deteriorate and crane beam is overloaded, numerous tensile and shear cracks will respectively develop on the vertical and inclined contact surfaces between the crane beam and surrounding rocks, which are macroscopically manifested as tensile fracture and slip failure. The above results are consistent with the three-dimensional finite element method. The proposed method also solves the problems of the finite element method that there is merely a single display method for surrounding rock damage and it is difficult to describe the changes of rock damage degree. This study provides a reference for investigating the macro- and meso-scopic characteristics and damage mechanism of large deformation and stress concentration areas of underground powerhouse caverns.

Key words: underground caverns, surrounding rocks, PFC-FLAC coupling, particle flow model, acoustic emission, meso-mechanism