Large-scale underground excavations usually pose a threat to the stability of the rock mass, and the damage is required to be modelled in order to plan the excavation schedule and support design. Various methods, such as displacement measurement, acoustic wave testing, and numerical calculation have been used to quantify the rock mass damage. In the present study, a microseismicity (MS) monitoring system was established to monitor the microcracks induced by excavation of the underground powerhouse at the Houziyan hydropower station in Sichuan Province, China and a damage-driven numerical model based on MS data was adopted to quantify the surrounding rock mass damage. The rock mass is simulated by a micromechanics-based constitutive model described by the fracture density, which is determined by the amount and size of the microcracks. The material property inputs for this model are Young's modulus, Poisson's ratio of the intact rock, and the MS information such as the location and the source size calculated from seismic source parameters. A typical profile of the underground powerhouse is selected for damage analysis. Combined with the excavation process, the related MS data is imported to the numerical model for damage calculation. The results show that the surface displacement of each bench excavation of the underground powerhouse using the damage-driven numerical model is approximately 30–40 mm larger than that using the original elastic model. Furthermore, the displacements of the rock mass considering the effect of MS damage are in good agreement with the field measurements.

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