Geotechnical Investigation of landslide and Geophysical Techniques: A Case of Tullu Gola, West Arsi zone, Oromiya, Ethiopia

Abstract

Landslides are one of the most destructive natural dangers, and they have a direct and indirect impact on a variety of human activities. On May 18, 2018, a landslide occurred in Tullu Gola Peasant Association, Nansabo district, West Arsi Zone, Oromiya Regional National State. The landslide destroyed more than 15ha of land, four dwelling houses, trees mixed with coffee, cultivated land, a dry-weather road, animals, grassland, and a tiny spring, as well as disrupting Tullu Gola's socio-economic operations. Therefore, the purpose of this work was to determine the causes of landslides by employing geotechnical conditions and geophysical techniques. Slope stability analysis of the research area was done using the finite element method (PLAXIS 2D version 8.2). To determine subsurface conditions, geophysical methods were conducted. Soil samples were taken from the top, right, left, and bottom of the slopes. The soil type of the study was dominated by fine-grained soils (silty), which was expected to be one of the triggering factors, especially during the rainy season. On May 18, 2010, this entry was published. The triggering factors that initiated the landslide, in addition to soil type, were heavy rainfall, deforestation, and various streams found along the landslide affected area. The landslide of the study area was also caused by inherent unstable geological structures, elevation, and steepness of slope. The factor of safety obtained in the affected area (the top side of the slope) was 0.62; in the same way, the factor of safety for the right side of the slope was around 1, which is in the range of an unstable slope. Remedial measures to mitigate landslide risk could be proper slope drainage to reduce water penetration, transferring dangerous settlement and leaving landslide alone (environment preserve, park), and stream train by gabion, which can be located at the higher and lower ends of the research area. Hence, the soil type of the study area was dominated by fine-grained soils and they influenced the occurrence of mass movement in the study area during the rainy season. The geomorphological conditions also play a great role in the stability problem of the study area. Stability conditions on the slope also exist in unstable conditions. Provision of surface drainage and engineering structures like gabion walls were forwarded as remedial measures to safeguard future failures of the slope of the study area