Regional Sensitivity Analysis of Slope Stability in Weathered Marly Soils: Parameter Ranking and Threshold Robustness at Moulay Yacoub, Morocco

Weathered marl hillslopes fail repeatedly across peri-urban Morocco, yet engineers investigating them rarely know which soil or geometric property most deserves their limited testing budget. This study answers that question for the landslide-prone slopes of Moulay Yacoub, in the northern pre-Rifian domain, by ranking the sensitivity of the factor of safety (FoS) to cohesion (c), friction angle (φ), unit weight (γ), slope height (H) and slope angle (β) under dry, deep-water-table conditions. Latin hypercube sampling generated 400 configurations over ranges drawn from site data; the FoS of each was computed by Bishop’s simplified method in Talren, and regional sensitivity analysis—the two-sample Kolmogorov–Smirnov statistic with a relative sensitivity index—ranked the five inputs. Cohesion governs the response by a wide margin (D = 0.470; 38.2% of total sensitivity at FoS = 1.2), ahead of slope height and friction angle (D ≈ 0.26); slope angle is marginal, and unit weight is not discriminating. Repeating the analysis at four thresholds (1.1–1.4) shows that the primacy of cohesion is threshold-independent, and that the apparent significance of slope angle at stricter thresholds is a statistical power effect, not a mechanical one. Site investigation in comparable marl settings should prioritise cohesion characterisation.