Swelling and Collapse of Unsaturated Soils Due to Inundation Under One-Dimensional Loading

Volume change of unsaturated soils is controlled by two stress state variables which are net normal stress and matric suction. Volume change phenomenon due to a change in matric suction or water content can be either shrinkage, swelling or collapse, and depends on the level of net normal stress and the initial void ratio of the soil. In this paper, consolidated kaolin specimens were air dried to various water contents and then inundated with water under different net normal stresses in order to study the wetting-induced volume change. The oedometer apparatus was used to carry out the swell test while the constant-rate-of-strain apparatus was used to carry out the constant volume test. The objective of this paper is to investigate the transition of swelling and collapse phenomenon due to different net normal stresses and to derive a method to estimate the wetting induced volume and net normal stress change of unsaturated soil. Based on the tests results, the pre-consolidation void ratio for the same soil before and after inundation is the same, the slope of the normal and unsaturated compression lines are the same under constant degree of saturation conditions and slopes of the unloading line under saturated and unsaturated condition are different. Based on the test results, a method to determine the wetting-induced swelling and collapse of unsaturated soils was proposed. The proposed method was verified using data from the literature.