Long-term behaviour of lime-treated expansive soil submitted to cyclic wetting and drying

Lime addition is a widely used technique to improve the engineering behaviour of soils and is known to reduce the swelling potential of expansive soils. However, in the long term, the permanence of the effect is questionable. This question is of interest since lime might be used to prevent swelling of expansive soils in earthworks. An experimental study was undertaken to assess the effects of successive wetting/drying cycles on the swelling behaviour of lime-treated expansive soils. This study was conducted both on three-year-old field samples from an experimental backfill and samples reconstituted in the laboratory. Osmotic suction-controlled oedometers were used to determine the swelling/shrinkage behaviour when submitted to wetting/drying cycles. The results obtained for reconstituted samples showed that lime treatment can reduce dramatically the swelling capacity of an expansive soil. However, the lime-treated samples taken from the experimental backfill exhibited important swelling and shrinkage deformations when submitted to successive wetting and drying. The results clearly indicate that treatment efficiency decreases with time. This tendency was confirmed by several cyclic wetting/drying tests.