Comparative Evaluation of Slope Reinforcement Techniques under Pseudo-Static Unsaturated and Rainfall Conditions

This study evaluates the combined effects of rainfall infiltration and pseudo-static seismic loading on the stability of an unsaturated silty soil slope, using an unreinforced baseline condition for comparison. The baseline slope is subsequently reinforced with soil nails, geogrid layers, and Vetiver grass (Chrysopogon zizanioides) roots to assess the relative effectiveness of each stabilization technique. Rainfall-induced infiltration was modelled to capture reductions in matric suction and the associated loss of shear strength, following which pseudo-static horizontal acceleration coefficients were applied to evaluate seismic response. Key parameters examined include factor of safety, deformation patterns, and failure mechanisms for the baseline and reinforced cases. Results indicate that rainfall significantly weakens the baseline slope prior to seismic loading, thereby increasing its vulnerability to earthquake-induced deformation. Soil nailing and geogrid reinforcement provide comparable improvements in the factor of safety after rainfall, with both techniques effectively controlling deformation. Vetiver roots enhance near-surface resistance but are less effective under stronger pseudo-static loading. These findings highlight the importance of considering both rainfall-induced weakening and seismic effects when selecting reinforcement methods for unsaturated slopes.