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The Dagangshan high arch dam , located in the area with complicated geological conditions and extremely high seismic intensity in Southwest China, has received substantial attention worldwide. Before the impoundment of the reservoir, continuous deep transverse cracks were observed in the low-elevation galleries of the arch dam. To investigate crack formation and propagation in the galleries of the high arch dam, microseismic monitoring and 3D finite element analysis of the galleries were performed during the filling process. The microseismic monitoring system was installed in the foundation gallery and the drainage gallery to detect microcracks around the galleries of the arch dam. The background stress field for crack formation and propagation in the galleries was studied based on 3D finite element modelling . The results indicate that the self-weight of high arch dam produces excessive circumferential tensile stresses at the arch crown of the galleries near the dam heel before impoundment, which is the cause of crack formation in the galleries of the Dagangshan high arch dam. As the impounded water level rises, the tensile stresses and the microseismicity in the galleries near the arch dam heel transfer to the galleries close to the arch dam toe, and the cracks in the galleries near the dam heel would not propagate further but be closed. However, cracking may occur in the gallery close to the dam toe if its microseismicity continues increasing. The conclusions have significant implications for reinforcement and operation of the galleries in similar high concrete arch dams.

The right bank slope of the Dagangshan hydropower station has undergone large deformation during excavation, which may continue to increase and cause slope instability and failure, threatening dam construction and safe operation. This study analysed the deformation and instability of this discontinuity-controlled rock slope by three-dimensional discontinuous deformation analysis (3D-DDA). A microseismic monitoring technique was adopted to capture the spatial and temporal distributions of microseismic events. The unknown geological discontinuities and the potential slip surface inside the slope were determined. By combining monitoring data with the geological information, the 3D-DDA model was established to analyse the 3D deformation characteristics of the slope. In addition, the slope deformation and failure under various conditions, such as over excavations, as well as various joint penetrations, joint dip directions, and friction angles were further investigated. It was found that the simulation of the critical sliding state of blocks by 3D-DDA is effective after improvement of the critical sliding model of joint contact between blocks, and the computational results showed good agreement with monitoring results. Slope deformation is caused by the accumulation of micro-crack damage in deep rock masses, and it is closely related to its internal and external conditions. Furthermore, the failure modes and mechanisms of the slope with 3D topography are presented, which may be helpful for the design of a slope reinforcement scheme.