Slope failure induced by cold snap and continuous precipitation in the seasonal frozen area of Qinghai-Tibet Plateau

Abstract

A slope failure of roughly 26,000 m3 occurred on September 7th, 2017 in the upper layer of a north-facing slope at Autumn Pasture in Zhimei Village, Chenduo County, Tibetan Autonomous Prefecture of Yushu (34°07′02.26″N, 96°37′10.90″E). Field investigations have indicated there is no continuous or discontinuous permafrost found in this area. The earth slope is susceptible to seasonal frost in freezing season and heavy rainfall in raining season. Hence, we hypothesized that the slope failure was induced by increasing pore water pressure at the basal surface, which resulted from the combined effect of a frozen upper layer and accumulated infiltrated soil water. With the accessible meteorological data from National Oceanic and Atmospheric Administration (NOAA), numerical software (CoupModel) was used to simulate the hydro-thermal state of the source area in order to explore the influence of atmospheric change and the triggering mechanism of slope failure. The simulation results indicate that an unexpected cold snap promoted the freezing process of the shallow soil layer, and the drainage of liquid water was impeded by this frozen layer. Accumulated downslope water at source area, namely the slope toe, led to the increasing of pore water pressure in the deeper parts of the soil. The source area is located in the catchment area, where water accumulated from surrounding slopes. Increased gravity of the upper layer resulting from downslope infiltrating soil water, and decreased shear strength of basal surface both contributed to the slope instability. The failure illustrated the influence of seasonal frost and sustained precipitation on mass wasting in Qinghai-Tibet Plateau (QTP).