Assessing static liquefaction triggering considering fabric anisotropy effects under the ACST framework

Previous experimental studies have shown that the onset of instability in sands under undrained loading is affected by the initial state (i.e., void ratio and confinement), intermediate stresses, and fabric anisotropy. These experimental results have motivated numerical studies that investigate the conditions for instability triggering; however, most efforts have been focused on triaxial conditions, mainly addressing the role of state with few notable exceptions that extend to a multiaxial setting incorporating fabric anisotropy. In this study, we use the relatively new anisotropic critical state theory (ACST) to investigate the onset of instability in sands under undrained loading considering the role of state, multi-axial loading, and fabric anisotropy. We use the ACST-based SANISAND-F constitutive model to extend a previously established stability criterion and take into account the effect of fabric anisotropy in a multiaxial setting. The analytical instability criterion is derived from the fabric-dependent constitutive equations, and predicts the plastic modulus and the flow stress ratio at the instability point. The derived criterion highlights the benefits of the ACST framework in incorporating fabric and anisotropy effects. Lastly, we show that the stress ratio at the instability onset is not significantly affected by the extent of anisotropic consolidation.