Retrospective Analysis and Stability Assessment of the SlopeAssociated with the Nangora Landslide, Loja, Ecuador:Geological and Geotechnical Implications

Abstract

The Loja–Malacatos road corridor exhibits recurring landslides that compromise slope stability and road connectivity. This study presents a retrospective analysis aimed at examining and understanding the dynamics, historical evolution, and triggering factors of the April 2025 event in the Nangora sector. The assessment was grounded in geomechanical characterization and analytical–numerical slope stability modeling. Although kinematic analysis indicated low susceptibility to structural failures (8.33% planar and 4.03 % wedge), limit equilibrium models demonstrated that slope behavior is governed by rock mass anisotropy (RMR = 58.2; GSI = 47). Isotropic models overestimated stability (FS > 1.2$), whereas anisotropic strength functions (ASF) reproduced critical conditions (FS = 0.96 static and FS = 0.64 pseudo-static). It is concluded that previous terracing interventions failed to mitigate the structural control, and that the event was driven by the progressive degradation of the rock mass and surficial saturation, rather than an extraordinary climatic anomaly.