Development characteristics and reactivation trend of Zhama ancient landslide in Batang, Sichuan

The Zhama ancient landslide is a large-scale one located in the Batang fault in western Sichuan. The remote sensing interpretation, field investigation and drilling revealed that the Zhama ancient landslide has a volume of about 2840×10⁴ m³. The Zhama ancient landslide has local resurrection features, which can be divided into two subregions, the rear collapse(Ⅰ) and slide body(Ⅱ). According to the landslide deformation, the slide body can be divided into the middle part of the local stable region(Ⅱ₁) and the front of the strong deformation region(Ⅱ₂, Ⅱ₃). Ⅱ₂ and Ⅱ₃ are bounded by the gullies at the front edge of the slope. Drilling revealed that two-level slip zones were developed in the Zhama landslide body. The location of two-level slip zones revealed by ZK1 was at 31.8~33.4 m and 77.7~81 m, and that by ZK2 was at 46.6~47.6 m and 68.2~69.8 m. The deformation of the Zhama ancient landslide was affected by heavy rainfall, earthquakes, and human engineering activities. At present, it is mainly local deformation.Secondary sliding occurs in the steep slope part of the front edge of the slope during the flood period. In the middle part, the landslide was induced by road excavation. The erosion ditch on the mountain caused small-scale debris flow under the action of heavy rainfall. The FLAC^3D numerical simulation of the Zhama ancient landslide indicates that under natural conditions, the displacement at the trailing edge of the landslide body is relatively large, causing the formation of moving landslide; under heavy rain conditions, shear deformation occurs on the trailing edge and the toe of the landslide body, and it is easy to produce a through sliding surface and a traction landslide along this surface. It is suggested from comprehensive analysis that under the influence of strong earthquakes, heavy rainfall, and human engineering activities, the landslide may resurrect as a whole along the sliding surface.