1D Free Swelling Model of Bentonite under Chemomechanical Coupling Action

Describing the time-dependent free swelling behavior of bentonite in saline solution is challenging as it is determined by the coupling effect of the chemical field and the swelling stress field in soil. The swelling pressure that determines the swelling strain of bentonite is affected by the ion concentration of pore water in soil, which in turn is affected by swelling strain. In this paper, a constitutive model estimating the 1D free swelling behavior of bentonite under chemomechanical coupling action is developed by incorporating the fractal swelling theory into the framework of the existing one-dimensional chemomechanical coupling consolidation model. A negative pore-water pressure is applied to substitute swelling pressure in the calculation model as it can produce the same effects on soil as the swelling pressure that drives the soil to adsorb water and swell in volume. The adsorbed water and swelling strain of bentonite increase with the dissipation of the negative pore-water pressure, or the release of swelling pressure. The model was verified by a one-dimension-free swelling test of bentonite in salt solutions. Furtherly, the influences of permeability coefficient and volume change coefficient of soil, and ion diffusion coefficient on 1D free swelling behavior were analyzed. The results suggest that the rates of the swelling pressure dissipation and the ion diffusion increase with the permeability coefficient, accelerating swelling to stabilize accordingly, whereas the effect of the volume change coefficient on the swelling rate is the opposite. The ion diffusion coefficient has a relatively small effect on the swelling pressure, while the final swelling strain is controlled by the additional pressure stemming from the osmotic suction of the ambient solution.