Dynamic failure mechanisms and hazard evaluation of rock collapse induced by extreme rainfall in Changbai County highways.

Rock collapses induced by extreme rainfall frequently occur along highways in Changbai County, posing serious threats to traffic safety and regional sustainable development. This study introduces a slope-unit zoning approach into the hazard assessment of collapses, integrating UDEC (Universal Distinct Element Code) numerical simulation and GIS (Geographic Information System) technology to reveal the failure mechanism and affected areas of slopes under extreme rainfall conditions. By employing the AHP-CV (Analytic Hierarchy Process-Coefficient of Variation) combined weighting method, the weights of nine critical indicators, including elevation, slope, slope direction, and NDVI (Normalized Difference Vegetation Index), were quantified. Pearson Type III frequency analysis was used to estimate rainfall recurrence periods, and the collapse hazard distribution under different rainfall probabilities was evaluated. The results indicate that areas of extremely high susceptibility are primarily distributed in steep slopes with fault development and sparse vegetation, accounting for 19.74% of the total area. Under a 100-year return rainfall condition, the proportion of extremely high-hazard areas increases to 38.68%. Increased pore water pressure and reduced shear strength along joint planes are identified as the primary causes of the tensile-collapse composite failure of slopes. The model achieved an AUC value of 0.908, demonstrating high reliability. This study overcomes the limitations of traditional grid-unit methods and provides scientific insights and technical support for the mechanism analysis, hazard assessment, and prevention of geological disasters under extreme rainfall conditions.