Instability analysis of a quaternary deposition slope after two sudden events of river water fluctuations

Abstract

On 10th October and 3rd November 2018, two landslides and the consecutive twice blockage of the Jinsha River led to sharp fluctuations of the upstream water level. These two events have caused numerous bank failures along the Ouqu River in the upper reaches. In this paper, a numerical model coupling the seepage and stability analyses was established, which was able to capture the fundamental behavior of geomaterials in both saturated/unsaturated conditions. Numerical results show that fluctuations of water level, permeability and shearing strength of the deposit were the key factors that had great influences on the seepage field and slope stability. The slope remained stable when the water level was rising since the water force acted as a back pressure. There was a critical rising level for the positive effect of rising water level, after which the variation of safety factor tended to be minimal. Differences in permeability determined the temporal saturated zone, whose properties consisted of not only the strength reduction due to the loss of suction in the zone affected by fluctuations, but also the instinct strength characteristics between different layers. Furthermore, permeability of the upper two layers had apparent adverse influences on the safety factor of slope.