Catastrophic submarine landslides with non-shallow shear band propagation

Submarine landslides are a geohazard encountered frequently in both shallow and deep waters. Catastrophic landslides are often related to strain-softening and shear band propagation (SBP). Limit equilibrium methods cannot capture this mechanism. The existing SBP theoretical methods treat slope failure as a progressive process of SBP, however, based on the shallow SBP approximation which is only valid when the length of the initial shear band is much larger than its depth. In this paper, catastrophic propagation of a deep-seated shear band is investigated via finite element analyses to understand and quantify the SBP at different conditions. The shallow SBP approximation is tested in a parametric study in terms of the relative depth of shear band and soil properties. An empirical correction equation is introduced to account for non-shallow SBP by modifying the existing failure criteria. The empirical solution is compared well with the FE results and can be implemented to assess submarine slope stability. The influences of different strain-softening relationships and inertia effects are discussed as well. As an example, the historical Storegga Slide offshore Norway is revisited, and the critical condition for its catastrophic failure is quantified using the proposed criterion.