Absolute Stability and Vegetation-Induced Stabilization in Root-Reinforced Slopes: A Factorial FEM-LEM Assessment

Vegetation-based slope stabilization is commonly evaluated from the final factor of safety, which can obscure whether an apparently favorable response reflects intrinsic slope resistance or the incremental effect of the vegetation treatment. This study tests whether the factor hierarchy associated with absolute stability differs from that associated with vegetation-induced stabilization and whether this distinction is preserved across limit equilibrium and finite element formulations. Seven fine-grained Andean soil classes, four vegetation systems, three slope geometries, and baseline and surcharge conditions were evaluated using laboratory-derived equivalent Mohr–Coulomb parameters. Each vegetated scenario was paired with an otherwise identical bare-soil reference, and the balanced numerical design was decomposed into factor and interaction contributions to variation across the investigated design space. Within the validated limit equilibrium domain, soil and geometry represented 72.1% and 26.6% of absolute stability variation, whereas species and soil × species represented 11.8% and 10.5% of relative vegetation-induced variation after normalization. Across 210 paired cases, agreement between methods was strong for absolute stability (r = 0.88; concordance coefficient = 0.83), but markedly weaker for vegetation-induced benefit. The results demonstrate a transferable distinction between the factors associated with system stability and those associated with intervention effectiveness. For engineering and restoration practice, plant selection should therefore follow site characterization and treatment-level numerical assessment, rather than a universal species ranking.