Performance Evaluation of a Tunnel-Slope System Under Heavy Rain-Fall Conditions

Intense rainfall, and the resulting increase in ground saturation can significantly modify the mechanical performance of rock masses in natural slopes. This is particularly important if material fractured is present. Extended infiltration accelerates material degradation, reduces shear strength along discontinuities, and increases pore-water pressures, reducing effective stresses, and in turn, raises the probability of large-scale landslides. Evaluating these processes requires a thorough understanding of the geotechnical and hydrogeological properties controlling slope response, as well as reliable stability assessments under varying saturation conditions, including factor of safety and deformation estimates. However, in engineering practice most of the time ground exploration is limited, and laboratory testing in rocks only provides an estimation of the rock performance expected in the slope within a reduced zone. This study examines a landslide triggered in a shale–limestone slope after heavy rainfall. A back-analysis was performed within a performance-based design (PBD) framework to reproduce the observed failure and, thus, characterize representative geomechanically parameters for design validation, using three-dimensional finite difference modeling. The performance under monotonic and seismic loading of a tunnel built adjacent to the slope was analyzed as a mitigation measure, thus establishing its technical soundness, from both state limit of failure and service, of the tunnel-slope system.