# Stability Analysis of the Huasushu Slope Under the Coupling of Reservoir Level Decline and Rainfall
## 2 Study Area  
Huasushu slope is located in Fengjie County, Chongqing City, Hefeng Township, Wenfeng Village, on the left bank of the Daxi River slope section. It is in the Dabashan table edge fold belt and the Sichuan Taikou intersection of the composite tectonic zone, and is characterized by complex geological conditions. The right boundary of the slope is a ridge, the left boundary is a gully, the back edge is a steep cliff, and the front edge extends to the bank of Daxi River, located at geographic coordinates 109\({}^{\circ}\)31'28.75\({}^{\prime\prime}\) E (longitude) and 30\({}^{\circ}\)55\({}^{\prime}\)22.09\({}^{\prime\prime}\) N (latitude). The elevation is about 214 m above sea level; the elevation of the front edge is about 155 m; the back edge reaches 310 m; the direction of the main slip is 151\({}^{\circ}\); and the topography as a whole presents a \"slow on top, steep underneath\" characteristic. The leading edge of the slope is in direct contact with the Yangtze River and is subject to scouring, forming a high and steep critical surface. A detailed map of the Huasushu landslide is shown in Figure 1.  
Huasushu is a secondary large-scale slope, with a total area of about 17.40 \(\times\) 10\({}^{4}\) m\({}^{2}\) and a volume of about 522 \(\times\) 10\({}^{4}\) m\({}^{3}\), consisting of upper loose accumulations and the muddy siltstone and sandstone of the Badong Group from the Middle Triassic in the lower part of the country. It has a loose structure and has many fissures. Slip surfaces have mostly developed along the contact surface between the slip body and the underlying relatively spaced cemented rocks, and seepage zones form easily, prompting slip behavior. Tension cracks have developed on the surface of the slope, with a width of 6 cm locally, showing certain creep-slip and traction deformation characteristics. This shows that the slope body is in a slowly developing sub-stable state. The formation of the slope can be traced back to 2006. At the initial stage, it showed deformation characteristics indicating the collapse of a steep wall at the rear edge, and the slope body was dominated by the deformation of a local small-scale slope. With the construction of Fengyen Highway, significant digging and filling construction changed the original equilibrium state of the slope, reduced its slip resistance, and formed a high and steep airside, creating conditions for the further development of landslides. This resulted in tension cracks in the road pavement approximately 28 m long and 3-6 cm wide. These cracks spread in a direction basically perpendicular to the overall slip direction of the slope. Figure 1: **(a)** Satellite view of the Huasushu slope. **(b)** Detailed view of Huasushu slope. After the initial period, the reservoir's annual cycle of rise and fall and regional heavy rainfall jointly influenced the water level of the Three Gorges project water storage area, causing the slope's evolution process to enter the next stage [31]. Given that the water storage increased to 175 m, the slope deformation clearly intensified. Long-term high-water-level immersion weakened the shear strength; the seasonal water level rapidly declined, inducing unloading; and rainwater infiltration triggered pore water pressure rise. All three of these factors jointly deformed the slope [32,33]. According to years of on-site monitoring data, deformation in the slope body is due to annual cumulative displacement, often caused by June-September rainstorms and water level drops during the same period of superposition. This reaches a peak, and the deformation rate increases by up to several millimeters per day; thus, the non-flooding season rate significantly slows down, showing a \"low speed-accelerate\" pattern. The deformation rate can then increase by several millimeters per day, due to the superposition of heavy rainfall and water level drops in September.