Shear Strength of Sodium Salt Contaminated Semi-arid Soil

Open dumping of industrial wastes and tailings can lead to infiltration and contamination of subgrade soils leading to a reduction in good quality pavement subgrades. It is therefore important to evaluate the properties of contaminated soils as well as the effectiveness of different methods of stabilization in order to secure the volume of potential pavement subgrade. The present work is focused on the laboratory investigation of the chemical properties, shear strength, and erosion-induced particle detachment of a compacted residual semi-arid soil which was treated with up to 10% salts of mixture of sodium phosphates and sodium carbonates. The effect of lime stabilization and inclusion of discrete polypropylene fibre on salt-treated soils before and after flume erosion was also investigated. The tests results indicated that soil treated with low concentration of salts exhibited brittle direct shear response, while higher concentration of salts (> 3%), induced a more ductile strain softening behaviour. Increase in salt dosage resulted in decreased mobilized friction angle of lime stabilized soil as well as increase in cohesion from 4 to 20 kPa. The change in shear strength parameters is due to high concentration of monovalent cation, 1:2 clay minerals, and anothite. The observed mass loss due to flume erosion was strongly correlated to pozzolanic index. Optimum soil performance in relation to mobilized shear strength, ductility, and resistance to soil particle detachment was observed for 8% lime stabilized soil with 1% fibre.