Influence of Acid, Base and Salt Contamination on Geotechnical Properties of Lateritic Soils from Southwestern Nigeria

Abstract

Pore water quality is often overlooked in geotechnical works and research. Samples of quartz schist-derived lateritic soil (S1) and granite gneiss-derived lateritic soils (S2) were mixed with solutions of varying pH spanning between pH 2 -12 and saltwater containing varying amounts of dissolved sodium chloride. The effect of this contamination on Atterberg limits, specific gravity, bulk density, compaction, California bearing ratio (CBR), shear strength, permeability and matric suction were investigated. Both soils contain kaolinite, quartz and goethite in varying proportions. Chemically, they contain silica, alumina, iron and titanium in order of abundance. Salt contamination resultsin reduced plasticity, specific gravity and bulk density. S1 samples which have higher kaolinite content exhibited greater reduction in these properties. Specific gravity and bulk density are highest for both soils when contaminated with alkaline water at pH 9. Optimum moisture content, permeability, cohesion and CBR reduced while maximum dry density and angle of internal friction increased with increasing salt contamination. Lateritic soils with the same mineralogy react differently to acid and base contamination due to variations in the minerals' percentage abundance. The presence of sodium chloride in the pore fluid of the soils caused agglomeration, a decrease in the diffuse double layer of their clay particles and cohesion.