Cyclic swell–shrink behaviour of an expansive soil treated with a sulfonated oil

The effects of a sulfonated oil (SO) stabiliser on the swell-shrink properties of an expansive soil were investigated through cyclic wetting-drying tests. The cyclic wetting-drying action led to the reconstruction of the soil microstructure by inducing clay particle aggregation. Accordingly, the greater the number of applied cycles, the lower the swell-shrink potential up to the fourth cycle, beyond which the swelling and shrinkage strains attained elastic equilibrium. At any given cycle, the tendency for swell-shrink reduction was in favour of the SO concentration up to 0.75%, beyond which the excess SO molecules self-associated in the form of aggregates, thereby acting as a 'lubricant' rather than a clay-stabilising agent. As a result of SO treatment, the accumulated axial strain progressively transitioned towards a desirable, 'neutral' state, with 0.75% SO exhibiting the highest resistance against cyclic wetting-drying. For any given SO concentration, the equalised void ratio-moisture content curves for wetting and drying followed the same S-shaped path, further corroborating that the swelling and shrinkage processes, on achieving elastic equilibrium, become reversible. The shrinkage and liquid limits indicated a progressive transition towards a desirable, aggregated fabric, with 0.75% SO identified as the optimum concentration.