Landslide Susceptibility Assessment using Geotechnical Index Properties of Soils in Ibam Edet and Odorokpe Villages, Ini LGA, Akwa Ibom State, Nigeria

Abstract

Susceptibility assessment of a landslide was carried out using the geotechnical index properties of soils in Ibam Edet and Odorokpe villages Ini LGA of Akwa Ibom State. The aim was to identify, characterize and evaluate the index properties of the soils in order to assess the susceptibility of the soils to a landslide. Soil samples were retrieved from three locations in Ibam Edet and one location in Odorokpe village using a hand auger from the ground surface to 4.0m depth. The samples were analysed in the laboratory to determine their index properties such as moisture content, Atterberg limits and particle size distributions. The stratigraphy consists of fine-medium grained clayey sand from 0-2m underlain by a medium-coarse grained sand from 2-4m depth in locations L1 and L2. In location L3, a fine-grained sand occurred from 0-4m. While in location L4 a fine-medium grained silty sand occurred from 0-2m underlain by a medium-coarse grained sand from 2-4m. The average moisture content percentages across locations L2 (37.3%), L3 (34.5%) and L4 (39.7%) showed a general decline in water content with depth.  While the liquid limit percentages increased with depth in locations L1 (29.6%) and L2 (26.5%). The presence of clays and silts in the sands between 0-2m in locations L1, L2 and L4 will limit the flow of water through the soil as shown in the higher percentages of moisture content and Atterberg limits in the clayey sand and silty sand layers. The particle size distribution plots of the sands show poorly /uniformly graded fine, medium to coarse grained sands that are free draining because of their high porosity and lack of cohesion.  An increased water saturation within the pores of the clayey sand and silty sands during prolonged and heavy rainfall reduces the friction and shear strength of the soil which may lead to landslides. This study therefore recommends the drilling and collection of soil samples at depths greater than 4m. Also, an analysis of the soils shear strength to evaluate the angle of internal friction of the clays and sands in order to quantitatively determine the slope stability, estimate the factor of safety and ascertain the degree of susceptibility of the soils to a landslide is recommended.