Effect of induced osmotic suction on swell and hydraulic conductivity of an expansive soil

Compacted expansive soils are widely used as engineered barriers in waste contaminant applications like landfills, brine ponds, and nuclear waste disposal sites. These liners are designed for very low hydraulic conductivity (<1 × 10−7 cm/s). Percolation of chemical waste or leachate results in physicochemical changes in compacted expansive soils which increases the hydraulic conductivity. This paper brings out the changes in swelling behavior and hydraulic conductivity of compacted expansive soil induced with osmotic gradients using NaCl and CaCl2 solutions. Multiple identical soil specimens placed in oedometer assemblies were inundated with distilled water, 0.4 and 4 M NaCl (monovalent cations), and 0.4 and 4 M CaCl2 (divalent cations) salt solutions and allowed to swell under a surcharge pressure of 12.5 kPa. Void ratio–water content plots were also traced during swelling process. Falling head permeability tests were conducted on swollen soil specimens in rigid wall oedometer permeameters under a hydraulic gradient (i) of 20. The experimental results showed that the swell potentials reduced and hydraulic conductivity increased with the increase in induced osmotic suction.