Stability and Deformation Responses of Earth Slopes Subjected to Multiple Natural and Manmade Hazards

Abstract

Multiple hazards such as rainfall, earthquake, and excavation may occur simultaneously, and the stability (factor of safety) and deformation (movement) behaviors must be investigated to prevent loss of life and properties. In this study, the stability and deformation behaviors of earth slopes subjected to the individual and simultaneous occurrence of these events are investigated using a coupled Geotechnical–Hydrological finite-element method (FEM). First, the finite-element model was validated against a case history and a widely used limit-equilibrium method (LEM) considering site-specific soil properties and rainfall records. The shape and the size of the critical failure surface obtained from the field investigation coincided well with those calculated using FEM and LEM. Also, the predicted onset of slope failure (after eight days of rainfall) coincided well with the real-time occurrence of the slope failure. The validated finite-element model was then used to predict the stability and deformation responses of earth slopes subjected to several possible scenarios, including individual and simultaneous occurrences of these events. The rainfall–excavation scenario indicated that the slope would have failed two days before the recorded time if the slope had a vertical cut width of 4.25 m. The rainfall–earthquake hazard scenario caused the slope to move horizontally by 799 mm. The parametric study conducted by varying the friction angle of the slope soil by ± one standard deviation (STD) with 10% covariance showed that the slope would have failed one day later and two days prior to the mean friction angle, respectively, when subjected to rainfall. Also, varying the friction angle by +1 STD and −1 STD failed the slope for 0.5 m above and 0.4 m below the cut width for the slope with mean friction angle when subjected to excavation, respectively. Further, the percent increase in the horizontal movement of the slope soil with friction angle by +1 STD and −1 STD compared to mean friction angle was 56% and 18%, respectively, when subjected to earthquake.