Yielding and flow liquefaction of loose sand

The relationship between the shapes of the yield surface and the undrained effective stress path (UESP) of loose sand is investigated for triaxial loading conditions. It is shown that the UESP can be used in the construction of capped yield surfaces for sands. The stress ratio M-p measured at a point where the UESP of loose sand reaches a peak, has been incorporated as a material parameter in the analytical relationship by which the yield surface is defined. The variations of M-p with void ratio, state parameter, and consolidation stresses are examined and compared with previous studies, in cases where such studies exist. It is shown that M-p is strongly influenced by soil dilatancy and anisotropy and its variation is remarkably consistent with the variation of soil strength and yielding stresses. Quantitative relationships for the variations of M-p are then introduced; these have been used elsewhere in constructing yield surfaces and modeling the constitutive behavior of sands. In addition to their use in modeling sand behavior, the yield surfaces and quantitative variations of M-p obtained here can be used in quantitative assessments of the susceptibility of loose sandy soils to flow liquefaction.