Factors inducing the Xigouwan landslide in the Three Gorges Reservoir area and the influence of antecedent precipitation

Abstract

Monitoring data over the years have shown that seasonal rainfall and reservoir level changes have always accompanied the accelerated deformation of the Xigouwan landslide, which makes it difficult to identify the dominant triggering factors of landslide deformation and poses a challenge to risk analysis. Given this, this paper analyzed the correlation between the daily deformation rate of the active and inactive areas in the Xigouwan landslide and rainfall, reservoir level, and the change rate of reservoir level by applying the attribute reduction algorithm of the neighborhood rough set model. The calculation results showed that the deformation in the active area was mainly affected by the rainfall in the past seven days. It was also related to the short-term change rate of reservoir water level in some ways. The weak deformation in the inactive area was related to the change rate of reservoir water level in the past three days. Then, based on the landslide deformation characteristics, it was further obtained that the average rainfall in the past seven days inducing severe deformation in the active area was about 20 mm. The decline of the reservoir water level influenced its deformation, but the effect was small. The reservoir level change affected the weak deformation in the inactive area with negligible influence, while the weak deformation in the inactive area was mainly influenced by the reservoir level change. Finally, the seepage-mechanics numerical analysis of the Xigouwan landslide reveals the deformation mechanism of the active area under long-duration early rainfall. As the rainfall intensity increased from 1 mm/d to 20 mm/d, the pore water pressure at the bottom of the landslide body gradually increased. The internal reservoir level rose and extended to the active area, which caused the landslide body in the active area to go from a stable state to an under-stable state, leading to large deformation in the active area. In addition, the numerical simulation results further showed that the decline of the reservoir level had little effect on the internal seepage field and the stability in the active area. The reservoir level change greatly influenced the internal seepage field in the inactive area, indicating that the weak deformation in the inactive area was mainly affected by the reservoir level change. The complete analysis results of factors inducing the Xigouwan landslide in this paper can help provide early warning. The average rainfall of 20 mm in the past seven days can be used as one of the early warning thresholds for severe deformation in the active area of the Xigouwan landslide.

Keywords

• xigouwan landslide
• triggering factors
• antecedent precipitation
• warning threshold
• geological disaster