Prediction of Wetting-Induced Swelling Using Effective Stress in an Unsaturated Kaolin

The wetting-induced swelling of unsaturated clayey soils can cause serious damages to buildings, bridges, and other infrastructure and may jeopardize the integrity of these structures. A model is required to predict these volume changes and be considered in the analysis and design of the structures. The volume change induced by wetting depends on many factors such as initial suction, net stress, effective stress, soil fabric, and suction history. Therefore, predicting the wetting-induced swelling is complicated. One of the tools for predicting the volume changes is the effective stress principle. However, the adoption of stress variables for prediction of unsaturated soil behavior is not consensus among the researchers in the geotechnical engineering field. In this paper, we employ the effective stress as a variable to predict the wetting-induced swelling of a commercial kaolin in unsaturated state. A series of oedometric tests are performed on 12 statically compacted kaolin specimens, prepared at three specific dry densities and various moisture contents. The unsaturated specimens are initially consolidated under certain vertical stress and then saturated while the total vertical stress is held constant. The wetting-induced swelling is measured at the end of saturation. One cycle of unloading-reloading is applied to the saturated specimens, and the vertical displacements are measured. The slopes of unloading-reloading paths are determined to be used in volume-change predictions. The prediction of wetting-induced swelling is based on two principles: (1) the validity of effective stress principle for unsaturated soils and (2) the applicability of elastic parameters at the saturated state for unsaturated conditions. The comparisons between the predicted and measured volume changes show the accuracy of this method in predicting the wetting-induced swelling for an unsaturated kaolin clay. The results of this research indicate that the effective stress approach is a powerful, yet simple tool for prediction of wetting-induced swelling in unsaturated clays.