The Occurrence of a Rainfall-Induced Catastrophic Landslide in a Soil and Rock-Like Stratum in Southwest China

A rainfall-induced catastrophic landslide occurred at 03:50 local time UTC+ 8 on August 21, 2020 in Zhonghaicun (29 degrees 20' 30'' N, 102 degrees 41'40'' E), Hanyuan County, China. Approximately 1.1 million cubic meters of debris failed instantly along the interface between the overlying soil and the Xigeda mudstone, destroying six buildings and causing nine casualties. The Xigeda stratum near the landslide consists of poorly lithified mudstone, which is characterized by weak cementation and unfavorable dip angle. The Xigeda stratum, as a locally distributed special formation in southwest China, is well known for the feature of "being prone to failure". In this paper, the mineral composition tests and mechanical strength tests were conducted to determine the physical and mechanical properties of the soil and rock-like stratum. In addition, numerical calculations were carried out to analyze the evolution of the Zhonghaicun landslide. The test results show that the Xigeda mudstone is a weakly swelling rock containing a large amount of clay minerals. The water content of the mudstone plays a significant role in its physico-mechanical properties. The heavy rainfall lasting approximately one week caused the water table to rise and the mudstone to soften, which eventually triggered the Zhonghaicun landslide.