DISCUSSION ON FAILURE MECHANISM FOR COMPLEX MOVEMENT OF SHUIMATUO LANDSLIDE IN GUIZHOU PROVINCE

At the beginning of 2011, affected by multi-periods of heavy rainfall, many geohazards were developed on the accumulated layer slopes in Shuimatuo Town, Sinan County. They include ground surface rupture, wall inclination, deformation aggravation of fissures on ground and walls. Once influenced by the heavy rainfall and other unfavorable factors, the unstable slopes would slide continuously, posing a serious threat to the 509 persons and 556 houses of Datong Community, and a significantly negative impact to the local society. Based on the field survey and indoor analysis, this paper elaborates the geo-environmental characteristics of the Shuimatuo landslide region and clarifies the important effects of geological structures and topographic conditions to the seepage field of the slope. With the help of local meteorological data, we continue to research the deformation and failure process of the slope under the rainfall condition with the SEEP/W module and the FLAC^3D software. We preliminarily expound the formation mechanism of the thrust-type landslide(H1) and secondary tractive landslide(H2)triggered by the multi-period of rainfall. The preliminary research results believe that induced by the rare heavy rainfall in the history, the major landslide begins to deform, but limited by the terrain condition, showing characteristics of part and progressive failure. During the long-term creep deformation process of landslide, rainfall causes a fluctuation of the groundwater level, strengthening the creep of sliding mass. Controlled by the free surface condition, the evolutionary process of secondary tractive landslide shows obvious correlation and certain lag comparing to the major landslide. For the thrust-type accumulated layer landslide, affected by the terrain, groundwater and loading conditions, it takes a long time from strength decrease of sliding belt to the formation of sliding plane. While tractive accumulated layer landslide lasts shortly as it is a backward movement generated by slope stress redistribution due to the lack of key anti-slide body.