Research on the Impact of Regional-Scale Soil Mechanics Parameter Disturbances on Rainfall Landslides Warning

The spatial uncertainty of soil mechanical parameters remains a major challenge in physical models for the prediction of rainfall landslides. Currently, the widely adopted stochastic methods for parameter selection disregard the lithological variations and fail to account for rainfall infiltration’s attenuation effects on soil mechanical parameters. Through field sampling and laboratory testing, this study examined the distribution of mechanical parameters across five lithological zones in Fengjie County, Chongqing, China. The soil mechanical parameters at liquid and plastic limits were used as boundaries, and nine attenuation scenarios of mechanical parameters were devised based on disturbance ratios from 0.1 to 0.9, simulating the attenuation effect of rainfall infiltration on parameters. The prediction performance across different attenuation scenarios was then explored. The findings revealed that different lithologies displayed unique normal distribution characteristics. Prediction results from slope units indicate lower disturbance ratios (0.1–0.3) yield ideal miss rates (below 10%) but very high false alarm rates. With higher disturbance ratios (0.4–0.9), missing alarm rates increased while false alarm rates continually decreased. At 0.4 disturbance ratio, both the false and missed alarm rates are optimal. This study recommends setting the disturbance ratio of soil mechanical parameters to 0.4 to achieve a preferable predictive performance in Fengjie County.