Main types of soil mass failure and characteristics of their impact factors in the Yuanmou Valley, China

Gully erosion is a dominant process causing soil loss in the Yuanmou Valley of Yunnan Province, China. Soil mass failure is a common process involved in gully development. The development of the gully and the occurrence of mass failure are interdependent and mutually promotive, but mass failure types have not been very well understood. In this study, we identify the main types of soil mass failure and the characteristics of their impact factors in the Yuanmou Valley. A detailed field survey was conducted in May 2010 in a representative area of the studied region, and selected soil parameters were measured in the field and laboratory. Results showed that there are four different soil mass failure types: falling, sliding, exfoliating, and toppling, each having unique characteristics of geology, topography, soil, and climate. Examination of these characteristics indicates that the occurrence of mass failure is controlled by four factors: 1) the typical geological structure of the Yuanmou Group represented by alternating layers of sand and clay; 2) the different terrain and landforms; 3) the different gully development stages; and 4) the particular soil properties under special weather conditions, including a dry–hot climate with distinct wet and dry seasons.