Non-uniqueness of flow liquefaction line for loose sand

It has been consistently observed in undrained triaxial tests (e.g. Casagrande, 1971; Castro et al., 1982; Vaid & Chern, 1985; Ishihara, 1993) that, subjected to monotonic loading, very loose sand exhibits a peak strength at a small shear strain and then collapses to flow rapidly to large strains at low effective confining pressure and low strength, as illustrated in Fig. 1. Furthermore, there exists an ultimate state of shear failure at which the sand flows continuously under constant stress and constant volume. The ultimate state, termed as steady state (Poulos, 1981), is...