Efficacy of lime-stabilised fly ash in expansive soils

The alternate swelling and shrinkage undergone by expansive clays due to moisture fluctuations causes substantial distress to structures built on such soils. Techniques such as sand cushions and ohesive nonswelling soil (CNS) cushions have been tried to arrest volume changes in these soils and hence prevent damage to structures. Sand cushions have been proved to be counterproductive. A CNS layer, though effective initially, became less effective after the first cycle of wetting and drying. Research carried out by the authors using a lime-stabilised fly ash cushion has shown that it is quite effective in arresting volume changes in expansive soils. A fly ash cushion, stabilise with 10% lime and with thickness equal to half that of the active zone in an expansive soil bed, educes heave by about 68% initially. With subsequent cycles of swelling and shrinkage the percent ge reduction in swelling is as much as 99·2%. Studies carried out on leaching have shown that only a small percentage of lime added to the fly ash leaches, even after five cycles of wetting and d ying. This shows the efficacy of the lime-stabilised fly ash cushion in minimising heave of expansive soil beds.