Geotechnical Assessment of Potential Mass Movement Occurrence in a Zone at Risk Around Yaoundé-Cameroon

Mass movements represent a major threat to human life, properties and infrastructures in most densely populated and hilly towns in humid tropical areas. The present work is focused on the evaluation of the safety factor of natural slopes of mount Eloumden, located at the West-South-West of Yaoundé, and on a contribution to address various problems related to the uncontrolled occupation of natural areas and the consequent potential mass movement occurrence. This natural slope stability study was carried out on the basis of field and laboratory tests: physical identification and geomechanical characterization of constituent materials from natural risk zone. The results obtained show that: the basement is made up of gneiss and the soil is ferrallitic; the constituent materials are silty-sand of the class A-6 (13) and A-6 (14), plastic, averagely water saturated, over consolidated and highly compressible. Their compaction can be tolerated when their preconsolidation stress is greater than their final effective stress; the short term factors of safety of these natural slopes, calculated on Excel, have values between 1.579 and 1.296 according to Fellenius for EL1 and EL2; 1.714 and 1.392 according to Bishop simplified. This infers that the slope EL1 is stable (Fs> 1.4) while the slope EL2 is potentially unstable (Fs<1.4).Depending on simulations, the factor of safety decreases progressively in the presence of groundwater flow; with the reduction of the cohesion and with an increase of the density of the wet soil.