SURFACE FRACTAL DIMENSION OF BENTONITE AND ITS APPLICATION IN CALCULATION OF SWELLING DEFORMATION

The correlation between the void ratio of swelled montmorillonite and the vertical overburden pressure can be expressed as ${e}_{{\rm m}} = Kp_{{\rm s}}^{{D}_{{\rm s}}-3}$. The surface fractal dimension Ds of five bentonites were estimated from the swelling deformation tests according to this fractal correlation. The reliability of surface fractal dimension obtained from the swelling deformation test was confirmed by nitrogen adsorption test, with identical values of surface fractal dimension obtained from both tests. The surface fractal dimension can also be used to estimate the swelling deformation of bentonite, after calculating the swelling coefficient K from the parameters of diffuse double layer (DDL) model in the osmotic swelling phase. Comparison of the model predictions with a number of experimental results on swelling deformation of both Na dominant and Ca dominant bentonites suggests that the surface fractal model works excellent in the cases tested.