A novel interpretation for the dilatancy behaviour of saturated clays

The dilatancy behaviour of clays significantly influences the stability and performance of underground engineering. In this work, comprehensive laboratory tests on both natural and reconstituted Shanghai clays are conducted to investigate the influence of natural structure and stress history (normal consolidation and overconsolidation) on the dilatancy behaviour. Meanwhile, comparative analysis is performed with data from the literature on Shanghai clays. Results indicate that reconstituted specimens, despite being normally consolidated, exhibit distinct dilatancy behaviours (i.e. shear-induced contraction and shear-induced dilation). Dilatancy intensifies as the overconsolidation ratio increases. The natural specimens from different layers tend to exhibit full contraction behaviour, influenced by their natural structure. Further investigation demonstrates that the confining pressure (p')–void ratio (e) states of specimens fundamentally control the dilatancy behaviours. Clays with denser states exhibit a marked tendency for shear-induced dilation, while those with looser states often display contractive behaviour. Based on these findings, a novel concept of the bounding compression line (BCL) is proposed, which captures the asymptotic convergence of Shanghai clays’ compression behaviour. By integrating the BCL with critical state soil mechanics, this work provides a unified interpretation of the diverse dilatancy behaviours observed in Shanghai clays.