Annual variation of landslide stability under the effect of water level fluctuation and rainfall in the Three Gorges Reservoir, China

Landslides in the Three Gorges Reservoir (TGR) are widely distributed and are a serious threat to the environment and the local people. Since the impoundment of the reservoir in 2003, many of the landslides have been reactivated which were triggered by water level fluctuation and rainfall. Taking the Maliulin landslide in the TGR as a case study, field investigation and displacement monitoring are conduced to study the characteristics of the landslide. According to the annual variation, the fluctuation of reservoir water is divided into four periods. The cumulative rainfall corresponding to different rainfall return periods is computed by Gumbel model. The variation of landslide stability and failure probability under the effect of water level fluctuation and rainfall in a complete annual cycle is calculated in terms of the Morgenstern–Price and Monte Carlo model. Based on the monitoring by inclinometer, a secondary shallow sliding surface is detected which controls its current activities. The annual variation of landslide stability tends to coincide with the change of reservoir water level. The minimum factor of safety occurs during the period of water level drawdown. Combining with the effect of extreme rainfall 50-year return period and water level dropdown, the calculated minimum factor of safety is below unit and the landslide is unstable. The scenario of annual failure probability of landslide is completed in the paper that is the basis for further risk evaluations.