Chemical, Physico-chemical and Geotechnical Properties of Lateritic Weathering Profile Derived from Granite Basement

Abstract

Disturbed and undisturbed soil samples were collected from a trial pit at depths of 0.5, 1.0, 1.5, 2.0, and 2.5 m. Chemical, physico-chemical and index properties tests were carried out on the disturbed samples while in-situ dry density and permeability tests were conducted on the undisturbed samples. California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) tests were carried out on specimens of the soil samples prepared at British Standard Light (BSL) and British Standard Heavy (BSH) compaction energy levels. Evaluation of the variation of chemical, physico-chemical and geotechnical properties of the lateritic weathering profile with depth were made. It was observed that the profile consist of a reddish pisolithic gravelly soil having a thickness of about 0.8 m between a light brownish silty to sandy soil from the top and a reddish fine lateritic soil bellow the horizon. Below this depth however, freshly decomposed granite base rock was encountered. The in-situ and recompacted dry densities as well as the natural and the optimum moisture contents increased to a depth of between 1.0 and 1.5 m after which the values decreased. The CBR and UCS values increased to a maximum of 106 % and 785 kN/m2 respectively at 1.5 m depth after which the values decreased. Therefore, the chemical, physico-chemical and geotechnical properties of the lateritic weathering profile studied varied with depth and should not be treated as the same.