Mineralogical, Geotechnical Characterization and Stability of the Cut Slopes of Widikum and its Surroundings (North-West Cameroon)

The Widikum highlands and its surroundings are located in the North West Region of Cameroon. These five last years, landslides are frequently affecting movement on this portion of the highway. An investigation for understanding the mechanism of these phenomena was recently performed to clarify and to propose suitable remediable solutions. The study included mineralogical and geotechnical characterization of the local soil materials. The X-ray diffraction mineralogical analysis on clay fractions reveals the presence of phyllitic minerals (kaolinite, gibbsite, montmorillonite, illite and biotite). Associated minerals are mainly represented by quartz. Montmorillonite has the small crystal and largest surface which aid in increasing its adsorptive capacity. Clayed minerals can cause swelling and consequently the change or variation of the mechanical characteristics of the materials. The natural water content of weathered products vary from 27 to 47.4% which are close or even lower than the liquid limit included between 59.4 and 71.9%, this justify their unstable character. In addition, the high plasticity index ranges between 17.9 and 29.3% and is indicative of plastic materials thus very sensitive to creep. Moreover, the saturation ratio is very high (60 - 96%) thus attesting to their quasi saturated state. It is advisable to reduce the height of the steps to 2.3m by opting for a bench of 3m and adopting an inclination angle of β = 37.5°. Building retaining structures as well as eucalyptus and vertiva grass planting is recommended to reduce landslide incidences.