Road-cut induced landslides along the Befang–Wum Ring Road (NW Cameroon): inventory, geotechnical characterisation and preliminary susceptibility assessment

Abstract

In tropical volcanic highlands, road construction frequently modifies natural slope geometry and hydrological conditions, thereby increasing landslide susceptibility. This study presents the first systematic inventory and slope-scale geotechnical characterisation of road-cut induced landslides along the Befang–Wum stretch of the Bamenda Ring Road (North-West Cameroon), within the Cameroon Volcanic Line. A total of 59 landslides were mapped, of which 20 representative failures were analysed in detail. Failures are predominantly shallow translational slides evolving into debris flows, with estimated volumes ranging from 17.5 to 6000 m³. Scarp heights generally remain below 5 m, indicating rainfall-triggered shallow instability rather than deep-seated structural collapse. Geotechnical analyses show low dry densities (1.00–1.22 g/cm³), bulk densities between 1.23 and 1.82 g/cm³, specific gravity values of 2.4–2.7, and moderate to high plasticity (PI = 11–35%). Soils are sandy–fine mixtures derived from deeply weathered granitic saprolite and pyroclastic deposits, dominated by kaolinitic–illitic clay fractions inferred from plasticity characteristics. Low density and moderate plasticity enhance rapid infiltration during intense rainfall, reducing effective stress and shear strength. Spatial clustering near Lake Ilum reflects combined geological, geomorphological and hydrological controls. Although individual failures are mostly small to medium in magnitude, their recurrence along the transport corridor poses persistent infrastructure and safety concerns. Improved drainage management, slope regrading, and bioengineering stabilization are recommended to reduce future instability. The study provides site-specific data necessary for improving infrastructure slope management in tropical volcanic highlands.