Use of shear wave velocity for assessing engineering properties of compacted bentonite after swelling

The characteristics of compacted bentonite after swelling determine the long-term stability of barrier systems. Due to the fact that the current stress level is the most important variable in determining the performance of engineered geosystems, this study aims to investigate the stress states and the consequent change in engineering properties of compacted bentonites after swelling. A series of vertical and horizontal swelling pressure tests were performed for compacted bentonites with varying initial dry unit weights at varying pore fluid concentrations. The compacted bentonite samples after swelling were loaded to investigate the changes in lateral stress and deformability. In addition, the shear wave velocity was continuously measured during and after swelling processes. The results of this study demonstrate that the swelling pressure increased with increasing dry unit weight of tested materials and decreasing pore fluid concentrations. The changes in lateral stress and void ratio of compacted bentonite after swelling were only measurable when the applied vertical stress was greater than the swelling pressure, reflecting that the swelling pressure cancels out the externally applied stress. Most notably, this study reveals that the initiation and termination of the swelling process and the change in engineering properties of compacted bentonite after swelling can be determined by measuring shear wave velocity.