Effect of Induced Osmotic Suction and Bentonite Content on Swell Behaviour and Hydraulic Conductivity of Compacted Red Soil

Abstract

Clay liners are integral part of both hazardous and municipal waste landfills that prevent leachate from percolating into the soil beneath and polluting it. Hence, the compacted soils must have very low hydraulic conductivity (<10^–7 cm/s) to act as effective clay liners. Locally available red soil may be used as a liner material as it satisfies the design criteria. To meet the hydraulic conductivity requirement, the locally available red soil was modified by adding 10% and 20% bentonite by dry weight. Multiple identical compacted specimens were set-up in oedometric assemblies under a surcharge pressure of 12.5 kPa and were inundated with distilled water, 0.4 M CaCl₂ and 0.4 M NaCl solutions to study the swelling behaviour of red soil and red soil modified with different bentonite contents. The specimens were compacted at their respective optimum moisture content values to their maximum dry unit weights. Falling head permeability tests were conducted to measure hydraulic conductivity using the rigid wall permeameters at a hydraulic gradient of 20 and surcharge pressure of 12.5 kPa. The nature of the inundating fluid and the bentonite content is seen to greatly affect the swelling behaviour and the hydraulic conductivity of the compacted red soil.