To assess the stability of large-scale underground caverns excavated in a layered rock mass with layers dipping steeply inside the surrounding rock, a high-resolution microseismic monitoring system was carried out in the right underground powerhouse of the Wudongde hydropower station in Southwest China. The progressive processes of layered rock mass damage including the initiation, propagation, coalescence and interaction of rock micro-fractures, was first demonstrated by analyzing the temporal and spatial distribution of microseismic activities. Meanwhile, the microseismic monitoring results were validated using conventional monitoring data and field observations. A typical failure of layered rock masses was fortunately monitored and the evolution of the microseismicity and its corresponding mechanism during the development of this studied failure were also obtained. The results can provide us an overall understanding of the progressive damage and failure evolution of large-scale underground openings in bedded rock masses.

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