ABSTRACT

An assessment of the geotechnical and hydrogeological properties as agents in the formation and expansion of gullies in Ikwuano area is presented. Field geological study of the area revealed that it is covered by sedimentary rocks. The soils are lateritic and are the product of intensive weathering that occurs under tropical and subtropical climatic conditions resulting in accumulation of hydrated iron and aluminium oxides. Results of sieves analysis show that the soils at the gully sites have sorting values ranging between 0.42 and 2.3, coefficient of uniformity values ranging between 3.0 and 10, and the coefficient of curvature values ranging between 0.2 and 1.3. These indicate that the soils are fair to well sorted in places. The plasticity indices values ranging between 11.0 and 29 with mean value of about 20 indicate soils of moderate to high plasticity, slight dry strength and easily friable. Value of maximum dry density ranges between 1.83g/cm3 and 2.12g/cm3 at optimum moisture contents of between 7.4% and 11.3% reveals that the soils were generally loose. The hydraulic conductivity and transmissivity values as determined from statistical grain size method range between 3.8 ×10- 4cm/s to 6.4 × 102cm/s and 3.8 ×10-2cm2/s to 9.6 ×104cm2 respectively. These indicate moderate seepage fluxes and adverse pore pressures and are thus easily erodible. From the geotechnical analysis results, recommendations for erosion control such as aforestration, construction of drainages and concrete rip-raps were suggested.