Physical Properties of Residual Profile Found in Minna

Abstract

Two trial pits, 6Km apart, were dogged to a depth of 5.0m each and both disturbed and undisturbed samples taken at the depths of 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0m. Tests including natural moisture content (NMC), liquid limit (LL), plastic limit (PL), mechanical sieve analysis, hydrometer analysis, specific gravity and Standard proctor compaction, were carried out on the disturbed samples while Insitu dry density and permeability tests were conducted on the undisturbed samples to evaluate the physical properties of the residual soil with depth. It was observed that the profile consists of a reddish lateritic soil layer having a thickness of about 0.8 to 1.7m, between a light reddish silty to sandy soil from the top and a whitish decomposed granite base rock below the layer. In area where water table was encountered before base rock, the NMC decreased to the reddish lateritic layer after which it increased down to the water table. But where otherwise, the NMC increased to the clay layer and decreased down to the base rock. The particle size distribution generally showed higher percentage of coarse soils at the reddish lateritic layer and higher percentage of clay size fractions at the layer just below the lateritic layer. The dry densities showed variation with depth but recorded higher values at the lateritic layer in both trial pits. Therefore, the physical property of the residual soils in Minna varies with depth and should not be treated as uniform.