The ancient landslides development characteristics and stability evaluation along the Luding Section, Dadu River, western Sichuan Province

The topography and geological structure are very complex along the Luding section of Dadu River, western Sichuan Province. The geological hazards, especially ancient landslides are extremely developed in this area. By means of remote sensing interpretation, InSAR deformation analysis and field investigation, 229 collapses, landslides and mudslides were discovered in the section from about 25 km upstream(to Guzan Town) to about 43 km downstream(to Detuo Town) of the Luding County. In addition, the ancient landslides in this area are large in scale, and some of them have signs of revival. The geological dating data show that the ancient landslides in this area were mainly developed in three periods around 120 ka, 25~10 ka and Holocene, and closely related to the activity of the Dadu River fault. The Dapingshang ancient landslide in Luding County was taken as a study case to analyze the stability of the landslide in natural state (self weight) and heavy rainfall state through ANSYS software. The results show that the stability coefficient of the landslide in natural state (self weight) and heavy rainfall state is 1.2 and 1.15 respectively. The stability coefficient under heavy rainfall conditions is lower than that under self-weight conditions; the deformation of the middle and lower part of the landslide tends to increase obviously under the action of heavy rainfall, and there is a tendency to slip along the empty surface of the slope. The slip surface is mainly developed in the medium weathered layer of the steep slope, but in the natural state, the potential slip surface is only formed in the loose accumulation layer in the middle of the slope and the upper part of the medium weathered layer. The developmental characteristics and stability of ancient landslides seriously affect the planning and construction of railway, highway, and hydroelectric power station projects. Therefore, it should be suggested to strengthen the identification, mechanism analysis and stability evaluation of ancient landslides.