Influence of suction on the strength and stiffness of compacted sand-bentonite

This paper examines the constitutive behaviour of unsaturated mixtures of compacted sand-bentonite material. Two different techniques have been used to modify soil suction in laboratory specimens to examine the influence of suction on the behaviour of compacted materials. The two methods generated inherent differences in material fabric and therefore in stress-strain behaviour. The difference in microstructure generated by these two preparation techniques created different properties for the two series of specimens. This paper compares the behaviour of the two series of specimens and relates the observed mechanical behaviour to the initial soil fabric created by the two different preparation techniques. Specimens of similar compacted material were taken from two full-scale in-ground experiments conducted at Atomic Energy of Canada Limited's Underground Research Laboratory at Lac du Bonnet, Manitoba and sheared using the same triaxial equipment. The results are compared to the results of shearing laboratory compacted specimens. The research program demonstrates the need to understand the initial volume and suction states of plastic clays in order to predict the change in mechanical behaviour following a change in water content.