GEOTECHNICAL PROPERTIES OF SOME SOILS ALONG OGUN RIVER AS EARTH DAM CONSTRUCTION MATERIALS

Small earth dams are important structures in the management of water resources for food security in developing nations. The construction of such dams at cheap rates depend on the availability of suitable earth material within the site location. The suitability of a given soil for use in earth dam construction is dictated by its geotechnical properties. The geotechnical properties of soils from three locations along the Ogun River in Iseyin, Nigeria, a predominantly farming community have been evaluated for their suitability as earth dam material. Although, the liquid limit (LL) determined for the samples are in the impermeable core zone, the samples from shoku (LOC3) has the lowest LL making it most suitable soil in terms of LL. the Soil from Ogunremi (LOC1) had the highest percentage large grains while the sample from Ajambata (LOC2) had the lowest. Soils from the 3 locations fall within the permeable shell zone which implies that without further enhancement, the soils will allow seepage when used for earth dam construction. The consolidation properties showed decrease in the coefficient of compressibility and coefficient of consolidation with increase in pressure in the locations. Coefficient of consolidation was peaked at 100-200 kN/m2 for LOC2, was least at 100-200 kN/m2 for LOC1 and decreased linearly with increase in pressure for LOC3. Samples from LOC2 and LOC3 exhibited better coefficient of consolidation than samples from LOC1 as the pressure increased within the 100-200 kN/m2 range. This is indicative of a relatively cohesive soil of medium shear strength. The investigation shows that the soil from all the location would need some form of improvement to make them adequately suitable as earth materials for dam construction. Further studies, would be carried out to address these needs.