Cyclic Swell-Shrink Behavior of a Low Plastic Expansive Soil

Low plastic expansive soils are widely distributed and commonly used as engineering material in arid and semi-arid regions. This paper addresses the swell-shrink behavior of a low plastic expansive soil. Cyclic swell-shrink tests were carried out in modified fixed-ring oedometers, in which samples were allowed to swell and either shrank fully in each wetting-drying cycle with constant surcharge pressure applied. Cumulative shrinkage or expansive deformations with increasing wetting-drying cycles were observed until an equilibrium state was reached. The number of wetting-drying cycles required for the low plastic expansive soil to reach equilibrium was much larger than that for highly expansive soils. On the other hand, the final deformations at equilibrium state after several wetting–drying cycles were larger than the deformations obtained from conventional oedometer test. The difference between them represents the additional deformation induced by cyclic wetting-drying, and is denoted as wetting-drying deformation. With increasing surcharge pressure, the wetting-drying deformation increases first and then declined after reaching its maximum at the preconsolidation pressure. The procedure used to derive the wetting-drying deformations in wetting cycles and drying cycles is also presented. It is found that more than 70% of the wetting-drying deformation occurred during the drying process. This phenomenon was attributed to the matric suction which greatly increased during the process of dehydration.