## 3 Landslide Deformation Zoning Characteristics  
### Surface Deformation Characteristics of the Landslide  
Ground fissures have appeared in the landslide since December 2018 and developed continuously since then. A total of 34 existing ground fissures and backfilled fissures have been investigated on site (Figure 5). Surface cracks on the landslide mass were found to be concentrated through density analysis of 34 cracks found in a ground investigation. Drainage ditches have been built according to terrain and runoff conditions to reduce the concentrated seepage of rainwater through cracks and to bury cracks. According to the deformation characteristics, sliding depth, main sliding direction, morphological characteristics, crack development characteristics, and stratigraphic characteristics of different parts of the landslide area, the landslide area can be divided into three main areas.  
Zone I is a shallow landslide with severe deformation. The sliding depth of the landslide is 10 m and the direction of sliding is 190\({}^{\circ}\). The leading edge shear outlet is located on the excavation surface of the upper road of the anti-slide pile. The shape is terraced. The existing lattice support at the rear edge of the landslide and drainage ditches were built around the support, which has greatly reduced the concentrated infiltration of rainwater at the rear edge. The main cracks in this area are arc tension cracks. The crack lengths are mainly 6-19 m; the longest is 30.4 m, and the average length is 12.1 m (Figure 6). It can be seen from Figure 5 that the cracks in Zone I are concentrated at the rear edge support, and their strike is perpendicular to the sliding direction.  
Zone II is in a stable state. It is a shallow landslide with a sliding direction of 233\({}^{\circ}\). The topographical gradient is generally flat and has been planted as farmland. There is no fresh deformation in this area, and a terrace exists at the rear edge, which is a sliding trace of the historical landslide. The west gully is the boundary of the landslide, and the leading edge shear exit is located on the top road of the anti-slide pile, which is not obvious now. The short surface cracks in this area are concentrated mainly in terraces at the rear edge, with an average length of 5-13 m (Figure 6). Crack strike is mainly perpendicular to the main slide direction.  
Zone III is the main sliding area, with a sliding depth of approximately 25-50 m. The terrain gradient is steeper at the rear edge and gentle in the middle, with a main sliding direction of 213\({}^{\circ}\). The leading edge shear outlet of the landslide is located in the middle of the anti-slide pile and at the bottom of the roadside retaining wall. Slurry is discharged from the retaining wall drain and the sliding zone is strongly weathered argillaceous shale. The boundary between the rear edge and both sides is a drainage ditch. The cracks are concentrated on the west side of the rear edge, with an average length of 18.6 m and a maximum length of 40.8 m (Figure 6). The crack length shows a normal distribution. Crack strike is approximately vertical to the slip direction. The purpose of investigating the surface crack information was to partition the deformation characteristics of the landslide so as to analyze the deformation mechanism of the landslide more accurately. The crack status has been repaired.  
Figure 5: Landslide deformation zoning: (**a**) Pond at the rear edge of the landslide; (**b**) Trailing edge; crack; (**c**) Dislocation of the landslide trailing edge; (**d**) Effluent from the drainage ditch; (**e**) Slip marks; (**f**) Drainage tunnel in construction; (**g**) Front edge drain; (**h**) Drainage ditch deformation; (**i**) Front edge uplift; and (**j**) Retaining wall water guide.  
Figure 6: Box diagram of crack length.