Slope stability modelling in Karongi district, Western Rwanda

Abstract. The Karongi District in Western Rwanda is frequently subject to landslides. To date, however, physics-based slope stability assessments remain pending. In this study, we apply a three-dimensional Limit Equilibrium Method (LEM) using Scoops3D software to compute Factor of Safety (FOS) distributions in Karongi District. The model evaluates the effects of the pore-pressure ratio (ru) and horizontal pseudo-static seismic coefficient (k_eq) on slope stability. Results identify critical thresholds at ru ∼ 0.10 and k_eq = 0.075, beyond which unstable areas expand rapidly. When combined to pore pressure and at low pore pressure ru ≤ 0.10, seismic loading can significantly amplify slope instability. Model validation using historical landslide inventories shows 80 % spatial agreement between simulated unstable areas (FOS < 1) and observed landslides in two scenarios: (1) ru = 0.18 and k_eq = 0.10; and (2) ru = 0.35 and k_eq = 0.03. Although applied to the Karongi district, the methodology presented in this study can be used to assess the relative importance of pore pressure and seismic forcing in slope stability in a seismically active region prone to landslides.