A methodology for evaluating liquefaction susceptibility in shallow sandy slopes

This paper illustrates a modeling approach for evaluating the liquefaction susceptibility of shallow sandy slopes. The methodology is based on a theoretical framework for capturing undrained bifurcation in saturated granular media. In order to provide predictive capabilities, the theory is combined with the MIT-S1 constitutive model. The role of a non-homogeneous density profile is investigated, distinguishing among the different forms of undrained response that can be induced by rapid shearing. The first part of the paper describes the general methodology and illustrates the use of a stability index for static liquefaction. In the second part, the practical significance of the approach is discussed by back-analyzing the well-known series of flow failures in an underwater berm at the Nerlerk site. The analyses predict that prior to failure the Nerlerk slopes were not yet beyond the limits of stability for incipient liquefaction. Model simulations, however, also indicate that very small shear perturbations could have activated an undrained instability. These results suggest that static liquefaction was a mechanically plausible failure mechanism and provide the first interpretation of the classical Nerlerk collapse based on the combined use of the theory of material stability and an advanced constitutive model for sands.