# Formation and Failure Mechanism of the Xinfangzi Landslide in Chongqing City (China)
## 4 Deformation Distribution and Composition of the Landslide  
According to the existing deformation of the landslide and the development characteristics of the surface cracks, the landslide can be divided into three areas: the main sliding area in the rear-central slip progressive area, the right loosely deformed area, and the front extrusion slump area (Figure 4). _The main sliding area in the rear-central slip progressive area (Area I)._ The sliding direction of the rear-central area was 342\({}^{\circ}\), which drove the overall sliding of the landslide. Area  
Figure 4: The section layout of the Xinfangzi landslide. I is longitudinal, and is about 302 m long and 104 m wide. It has an area of about 3.14 \(\times\) 10\({}^{4}\) m\({}^{2}\), a thickness of 4.1-33.6 m, an average thickness of 19.54 m, and a volume of about 61.37 \(\times\) 10\({}^{4}\) m\({}^{3}\). The sliding mass of Area I is mainly composed of ancient landslide debris and later accumulated rocks caused by the collapse. The length of the rear tension crack slot in this area is about 11-16.5 m, the width is about 1.5-3.5 m, and the visible depth is about 1.6-3.9 m. The left boundary of Area I moved downward by about 2.3 to 7.8 m as a whole, and the length of the falling ridge is about 450 m. In addition, the soil of the shear outlet at the right front side is loaded on the slope, causing a local slump. _The right loosely deformed area (Area II)_. Area II is a long strip with a length of about 240 m and a width of about 3-12 m. It slid in the direction of 45-60\({}^{\circ}\) under the control of steep local ridges (rural road slopes). A total of five small landslides were formed in this area, with volumes of about 5 to 400 m\({}^{3}\), covering the roadbed. _The front extrusion slump area (Area III)_. Area III slid in the direction of 13\({}^{\circ}\) under the push of Area I. This area is fan-shaped, with a length of about 113 m, a width of about 84 m, an area of about 0.95 \(\times\) 10\({}^{4}\) m\({}^{2}\), a thickness of 7.8-25.5 m, an average thickness of 16.3 m, and a volume of about 15.47 \(\times\) 10\({}^{4}\) m\({}^{3}\). The deformation of this area was mainly the formation of a penetrating step, with a height of about 0.5 to 2.6 m, on the left backside under push. Plume cracks were formed by squeezing and shearing. Part of the soil in this area collapsed from the front edge of the shear outlet to the G210 national road. According to the drilling results (Figure 5), the thickness of the sliding mass is about 4.1-33.6 m, with an average thickness of 18.5 m. The sliding mass at the trailing edge is mainly mudstone intercalated with sandstone residues after slippage disintegration, with a thickness of about 2.7 to 31.8 m. The sliding mass in the middle and front part is mainly composed of silty clay and stone soils, with a thickness of about 23.4 m.  
The slip zone in the rear of the fragmented rock is a soft and muddy interlayer between the layers. The drilling results indicate that this part of the slip zone exhibits slip and tension in a 1.50 m area, and obvious scratches were observed. The slip zone in the middle-front part of the soil is the breccia of the rock-soil interface, which has a dense structure and obvious extrusion characteristics. The slip bed is the bedrock of the interbedded mudstone and sandstone of the Middle Jurassic Shaximiao Formation, with a burial depth of about 4.10-33.6 m. The front and right edges are shallower, and the rear and left edges are deeper. The groundwater in the study area distributes in loose rock pore, landslide rock debris fissure, and bedrock fissure. The water in the boreholes was drained to observe the dynamics of the water level. After 24 h, the groundwater level at the rear part was 0.20-11.50 m, and that in the middle-front part was 0.2-16.65 m. In addition, the water level in the borehole increased significantly after rainfall. Notably, the groundwater levels in the boreholes were quite different, indicating that there is no stable groundwater level for the entire landslide.