Erodibility characteristics and slope stability analysis of geological units prone to erosion in Udi area, southeast Nigeria

In Udi province, gully erosion has caused several environmental damages such as loss of agricultural lands and natural vegetation, loss of residential apartments, destruction of engineering structures, and disruption of wildlife ecosystem. In this paper, an attempt was made to assess the erodibility characteristics and slope stability of geological units prone to erosion in this area using integrated approach. Geotechnical analysis of soil samples revealed that they are susceptible to erosional processes. The soil samples were classified as poorly graded sands and silty sands based on Unified Soil Classification System. Grain size distribution analysis showed that the soils were almost devoid of clays, which could serve as binding materials. Atterberg limit test revealed that they were nonplastic. Compaction test indicated that the soils were loose and collapsible, with dry density ranging from 1.65 to 1.96 g/cm(3). On the basis of permeability coefficients (which ranged from 6.81 x 10(-5) to 1.28 x 10(-4) m/s), the soils are moderately to highly permeable, indicating high infiltration capacity. Shear strength analysis revealed that the soils have low cohesive capacity (ranging from 0 to 5 kPa) and relatively low angle of shearing resistance (ranging from 22 degrees to 30 degrees). Multivariate statistical analyses aided the establishment of the interrelationships between the analyzed geotechnical parameters. The obtained factor of safety of the gully slopes (in both saturated and unsaturated conditions) ranged from 0.81 to 0.90 and 1.02 to 1.41, respectively. This indicates that the gully slopes are typically unstable in saturated conditions and critically stable in unsaturated conditions.