Joint spatial variability of depth to bedrock, hydraulic, and shear strength parameters in 3D landslide prediction

Landslides in unsaturated slopes result from complex and uncertain interactions among rainfall infiltration, soil hydraulic and mechanical parameters, and subsurface geometry. While these factors have been widely studied in isolation, their combined influence under fully three-dimensional and transient conditions remains insufficiently explored. This study develops and applies an integrated probabilistic framework for slope stability analysis that explicitly incorporates the spatial variability of shear strength, hydraulic parameters, and bedrock surface geometry. The framework combines the Stepwise Covariance Matrix Decomposition technique for random field generation, transient pore-pressure simulation via Richards equation, and Numerical Limit Analysis to evaluate failure mechanisms. It is applied to a tropical hillslope in Rio de Janeiro, Brazil, using site-specific geotechnical and hydrological data. Slope stability is evaluated at multiple time steps during a 22-day extreme rainfall event, following a 180-day spin-up period to establish realistic initial conditions. Results reveal that bedrock variability exerts dominant control on pore-pressure evolution, while spatial fluctuations in cohesion primarily govern failure extent and timing. Initial failures occur in zones characterized by low cohesion, low hydraulic conductivity, and thin soil cover. These findings underscore the importance of jointly modeling multiple sources of spatial uncertainty to improve the reliability of landslide hazard assessments in tropical environments.