Formation and Failure Mechanism of the Xinfangzi Landslide in Chongqing City (China)

At 2:00 a.m. on 1 July 2020, after several days of continuous heavy rainfall, the Xinfangzi landslide occurred in Zhengping Village, Ganshui Town, Qijiang District, Chongqing City, China. The area of the landslide was about 3.85 x 10(4) m(2) and the volume was about 71.22 x 10(4) m(3). The Xinfangzi landslide can be defined as a push-type landslide. Specifically, the main sliding area pushed the front squeezing area, causing it to slide laterally. The entire slip path of the landslide was a broken line, while the right edge and the front shear outlet position slipped loosely in a circular arc. In this study, finite element numerical calculations were used to compare and analyze the multisection plastic deformation of the landslide under natural and rainfall conditions based on field investigations. The formation and failure characteristics of the Xinfangzi landslide were further revealed. The results show that the cross and longitudinal sections of the landslide were in a critical state of instability under natural and rainfall conditions. A compound section was established along the slip path based on the cross and longitudinal sections. Due to the extrusion of the trailing edge of the landslide, the compound section's leading edge was in a state of instability under natural conditions. Under rainfall conditions, the increase in the unit weight of the sliding mass was superimposed on the compound section, which amplified the thrust of the trailing edge and further accelerated the overall sliding process of the landslide. Based on the macroscopic deformation of the landslide, it was found that the sliding of the trailing edge of the landslide is the key factor promoting the failure of the front edge, and local slump is possible under rainfall conditions.