Experimental study on air-dried shrinkage and frozen deformation characteristics of unsaturated bentonite

Saturated bentonite swells during freezing while unsaturated bentonite may shrink during freezing, which may be related to the water loss-induced shrinkage and ice-water phase transition-induced expansion. In order to investigate the contribution of these two parts, the bentonite samples with various void ratios and degrees of saturation are examined using the frozen deformation tests, air-dried shrinkage tests and freezing point tests. The test results demonstrate that the freezing point of the unsaturated bentonite mainly depends on its gravimetric water content and is much larger than that of unsaturated silt clay. The sample with high density becomes loose and the one with low density becomes dense after being frozen. The bentonite samples with low degree of saturation, i.e., 0.4, 0.5, 0.6, 0.7, shrink, whereas the sample with high degree of saturation (0.9) swells after being frozen. A linear relationship is found between the volumetric ice content and the ice-water phase transition-induced volumetric deformation, which is a comprehensive reflection of the influence of degree of saturation, void ratio and temperature on the deformation of unsaturated bentonite.