Deformation characteristics and failure mechanisms of a rainfall-induced complex landslide in Wanzhou County, Three Gorges Reservoir, China

A rainfall-induced complex landslide occurred on April 4, 2013, in Wanzhou County, Three Gorges Reservoir, China. Approximately 1.5 x 10(6) m(3) of earth and rock mass slid over a distance of 30 m, destroying residential buildings and rural roads. We perform a comprehensive assessment of the cause of this landslide using field surveys, borehole drillings, and interpretations of aerial photographs. This landslide exhibited a complex failure mode in which the upper part of the earth slope first deformed and slid along geotechnical interfaces. This then triggered the slide of the lower part of the flysch bedding rock. In this study, the landslide mass was divided into nine separate blocks considering their internal geological features and movements. The study also shows that antecedent rainfall, in association with the geological and morphological features of the steep slope, the presence of weak interlayers, and human interventions such as slope excavations, jointly caused this disaster. This well-observed event study facilitates comprehensive recognition of the deformation characteristics and failure mechanisms of rainfall-induced complex landslides and also provides an insight into landslide hazard mitigation.