Investigation of geotechnical characteristics and slope stability analysis of landslide: the case of lalisa village, tiro afata district, jimma zone, oromia, south-west Ethiopia

Abstract

Landslide is the most damaging natural disaster at global and local level. Landslide could cause damage of farm and grazing land due to ground subsidence, large cracks and soil mass movement. Livelihood, ecological and human health disturbance and destroy animal life are another impact of the study area landslide. Recently, landslide has occurred in Lalisa village, Tiro Afata District, Jimma Zone, Oromia. Therefore, this study particularly aimed at identifying geotechnical characteristics, type of soil and their role in landslide initiation, slope stability analysis for those not failed by taking the samples within a certain distance from the failed soil to identify causes for the happened landslide in Lalisa village. The approached methods were field work, laboratory and software analysis. Measurement of slope geometry and landslide size, geophysical resistivity to know type of soil, level of ground water and thickness of weak zone without soil structure disturbance were conducted in the field. Laboratory tests using American Society Test Material standard were conducted to determine grain size, Atterberg limit, natural moisture content, shear strength and specific gravity. Slope stability was analyzed using Geostudio Slope/W. The results revealed that the soils were clay, which deform like a plastic material even semiliquid when in contact with excess water. This characteristics of soil were considered as sensitive for swelling and shrinkage when in contact with water and dries respectively and high intensity of rainfall increase the pore water pressure in the soil and decrease shear strength as a result slope failure. The Geostudio Slope/W result shows that the factor of safety the slope less than unity even in modified slope angle, which was unsafe and this was due to the effect of slope steepness. The factor of safety for modified slope angle was higher when compared to natural slope. This could be due to the effect of steep slope. Additionally, the finding suggest that in case of modified slope gradient and increase distance from failure surface the factor of safety increased by by 47 %. These reveals that making slope gentle and free from cultivation within a certain distance are used as a prevention methods of the landslide of study area.