Geotechnical Properties and Stability of a Landslide Site in South Eastern Nigeria

Abstract

The geotechnical properties and the stability of a landslide site in south eastern Nigeria were assessed. The soils associated with the landslides have low bulk density, high porosity and permeability. The slip surface was impermeable black shale. The landslide site is under intense hydrostatic pressure manifested in numerous springs and oil (gasoline) seepage. Shearing tests show the shear strength parameters are very low, and that the dominant process controlling the deformation of the soils was liquefaction. Normally and over-consolidated samples all liquefied, with over-consolidated samples having higher brittleness index than the normally consolidated ones. Scanning electron microscope analyses show that there are micro planes of weakness in the undisturbed soil samples meaning that the soils are inherently unstable and needs only a minor increase in shear stress on the slope to fail. Significant excess pore pressure generation began only after the soils had been displaced considerably. Stability analysis obtained a factor of safety of 0.78. The concern is that about 95% of the slopes in south eastern Nigeria are founded on soils with similar properties investigated. Urgent action is needed, therefore, to prevent further loss of lives and property.