MECHANISM OF GRADUAL RETREAT LOESS LANDSLIDE CAUSED BY GROUNDWATER: A CASE STUDY OF THE IRRIGATION LOESS LANDSLIDE IN HEIFANGTAI, GANSU PROVINCE

Heifangtai is located in Yongjing County, Gansu province. The loess landslide is very developed due to irrigation. One of the most typical landslides is the gradual retreat of the loess landslide caused by long-term irrigation. This paper compares the Google images and the field survey of representative landslide occurred in recent years. It shows that the loess landslides have the characteristics of gradual recession. It further investigates and analyze the water content of the loess landslide profile. It finds that the main reason for loess landslide occurred continuously are soft base effect formed by long-term soaking of groundwater. The arc groove of the landslide often becomes the concentration of groundwater and drainage points. The residual landslide accumulation in slide source area rises the local underground water. It is the main reason to make the same position more and more gradual retreat type landslide.