An Empirical Swelling Pressure Kinetics Model for Bentonite and Bentonite-Based Materials Hydrated under Constant Volume Conditions

Swelling pressure (SP) is one of the most basic properties of bentonite and bentonite-based materials. To date, extensive models have been proposed for predicting SP. However, most of the existing models are aimed at predicting the final steady SP at saturation, ignoring the development process of SP during hydration. In this study, the SP was considered as a result of competition between the accumulated wedging pressure (AWP) and dissipated wedging pressure (DWP) within the specimen. By assuming that the AWP increases continuously with infiltration time following an exponential function and that the DWP first increases and then decreases with infiltration time obeying the Weibull distribution, a new empirical model for modeling the SP kinetics was established. The model contains only five parameters, which all have definite physical meanings and are susceptible to various factors including the mineral composition, dry density, specimen dimensions, infiltrated solution concentration, and temperature. The model was verified with three types (I, II, and III) of experimental SP kinetics on bentonite and bentonite-based soils. Results show that the model is capable of modeling the SP kinetics of Types I and II, while for SP curves of Type III, the simulated results deviate significantly from the experimental ones due to the model ignoring the second decrease of SP induced by montmorillonite dissolution in the high alkaline solutions. Furthermore, a four-step simplified procedure for predicting SP kinetics at different dry densities was put forward and verified by experimental results of MX-80 bentonite pellet/powder mixtures and compacted GMZ bentonite.