Microseismic monitoring and stability analysis for the large-scale underground caverns at the Wudongde hydropower station

To analyse the stability of rock mass subjected to excavation of the underground caverns at the Wudongde hydropower station, a high-resolution microseismic (MS) monitoring system was applied. Based on the temporal evolution characteristics of MS events, the relationship between construction state and MS activity was established. Combining the spatial evolution characteristics of MS events with traditional monitoring, geological survey and field observation, several main damage regions were identified and the key factors causing rock mass damage were revealed. Furthermore, the evolution laws of MS source multi-parameters during the large deformation of rock mass were systemically analysed. Prior to the large deformation of rock mass, the MS source multi-parameters behaved differently, including an obvious increment of the number of MS events, a sharp increment of the energy index with a progressive increment of the apparent volume and a decreasing trend of the centre frequency. The present study reveals that the integrated analytical method incorporating MS monitoring, traditional monitoring, geological survey and field observation leads to a better understanding of the behaviour of surrounding rock mass subjected to excavation, which is of great significance for the risk management of rock mass deformation and failures in the large-scale underground caverns.