Geotechnical Evaluation of Gully Erosion and Landslides Materials and their Impact in Iguosa and its Environs, Western Anambra Basin, Nigeria
Background: Field survey and geotechnical evaluation was done to determine the soil characteristics of the gullies and landslides materials and their impact in Iguosa and its environs, Western Anambra Basin. This was done to explain and evaluate the root problems, causes, mechanism of the continuous gullies and landslides in the study area.Results: The field study reveals that the geomorphological characteristics, weakly developed structures, slope steepness, wrong use of the land and poor
... land and poor vegetation cover coupled with intense and prolonged rainfall contributed to the origin, causes of gullies and landslides in the study area. Geotechnical parameters for soil samples in the study area shows that the mean liquid limit (LL) of 40, mean plastic limit (PL) of 8.30, mean plasticity index (PI) of 21.20, mean coefficient of permeability (K) of 3.65 × 10cm/sec, mean cohesion and mean angles of internal angles between grains of 2.56 kƿa and 23.70 respectively. The low PL, low LL and low PI values of the Ajali sand, low cohesion (poor compaction) and low angle of internal resistance between grains of the soil, high K of Ajali sand coupled with the swelling and shrinking nature of the clay beds beneath the Ajali sand, resulted to easily weathering of the Ajali sands, erosional and continuous landslide activities in these affected areas.Conclusions: The origin, mechanism and impacts of landslide hazards have been investigated in Iguosa and its environs, Western Anambra Basin, Nigeria. Field observation reveals that the geomorphological characteristics, weakly developed structure, high slope instability, wrong use of land, as well as the steepness of the slope and intense and prolonged rainfall contributed to the origin of landslide as well as the gully erosion in the study area. The unconsolidated nature of the soil, less cohesion, high permeability, and weak plasticity of the soil that occurs under and above the clay lithologic units (gliding planes) contributed to landslide and gully erosion. Possible prospective implications of the gully erosion and landslides in the study areas are land degradation, destruction of houses and other properties, farm lands and roads. The following suggestions have been made to solve these problems by covering the landslide areas with impermeable layers/materials, diverting surface water away from the landslide areas, enacting laws to prevent erection of structures on landslide prone areas, the use of biotechnical slope techniques and bioengineering methods. The application of these recommended methods will go a long way in solving the problem of landslide hazards in the study area.