EFFECT OF ANISOTROPIC YIELDING ON THE FLOW LIQUEFACTION OF LOOSE SAND

S. M. Reza Imam, Dave H. Chan, Peter K. Robertson and Norbert R. Morgenstern

ABSTRACT: In very loose sand, the ratio Mp of shear stress to mean normal stress at the peak point of the undrained effective stress path (UESP) is very close to the stress ratio M at the peak point of the capped yield surface. Stress ratios Mp can therefore be used in constructing yield surfaces of sands. These stress ratios have also been used in the past in evaluating flow potential of loose sand. Application of Mp for these purposes requires that factors affecting this stress ratio, and quantitative relationships for the variation of Mp with these factors be determined. In this paper, effects of the intermediate principal stress and direction of loading on Mp are investigated, and models are developed by which these effects can be quantified. It is shown that variations of Mp with these factors are similar to the variations of yielding stresses obtained from stress-strain data. Yield surfaces obtained from the variation of Mp indicated a strong dependency of yielding stresses on inherent anisotropy. Data examined in this paper also suggest that the effects of inherent anisotropy on yielding stresses are controlled primarily by the relative magnitudes of the normal stresses applied in the principal directions of material anisotropy.

Keywords: Anisotropy, yield surface, loose sand, liquefaction, constitutive modeling, instability (IGC: D6/E6/E7)