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.
