On the undrained strain-induced anisotropy of loose sand

An experimental study was carried out to investigate the effects of previous deviatoric strain histories on the undrained behaviour of loose and saturated Toyoura sand and compared with known results of Hostun RF sand. From an initial isotropic stress state, recent deviatoric strain histories in the compression side of the triaxial plane were generated by a standard drained presheared cycle up to a specified mobilized stress ratio. Mainly, the fully liquefied, contractive, unstable and softening behaviour of loose sand was progressively transformed into the non-liquefied, dilative, fully stable and hardening behaviour of dense-like sand, while remaining within a narrow range of loose density. The paper validates and extends the current understanding of strain-induced anisotropy of loose sand. New experimental data support the directional dependency of the instability cone on the stress increment direction, suggest the bifurcation characteristics of loose sand and evidence the important role of past deviatoric strain histories.