Microseismicity and its time–frequency characteristics of the left bank slope at the Jinping first-stage hydropower station during reservoir impoundment

Abstract

The instability risk associated with the left bank slope of the Jinping first-stage hydropower station in south-western China may increase as a result of the initial impoundment of the reservoir and the raising and lowering of the reservoir level. To improve our understanding of the rock slope stability and the real-time behaviour of the composite system of rock slope and dam, an existing microseismic (MS) monitoring system installed on May 2009 was improved in early 2014. This investigation represents the first time such a technique has been used to evaluate the stability of a high rock slope in China. The safety and maintenance of the rock slope during the reservoir impoundment were investigated through the development of fast and accurate real-time event location technique aimed at assessing the evolution and migration of the seismic activity and through the development of capabilities for forecasting the rock slope stability. Numerous MS events in the rock slope have been recorded using the MS monitoring system. Zones of damaged rock mass were identified based on a spatio-temporal analysis of the seismic activity during the impoundment period. Moreover, a waveform decomposition method based on the S transform was proposed for processing the seismic waveforms during the construction and impoundment periods of the left bank slope, and the time–frequency characteristics of seismic events during these two periods were thus compared. The understanding of the relationships between the time–frequency parameters variations in the seismic signals and the rock mass damage can provide a basis for evaluating the stability of similar rock slopes.