Transition from shear band propagation to global slab failure in submarine landslides

Risk posed by seabed instability is of increasing significance as offshore activities including oil and gas developments continue to expand in this century. Many studies have considered runout of debris flows resulting from submarine landslides and potential impact on offshore infrastructure. However, initiation of slab failure resulting from shear band propagation (SBP) at the onset of a landslide has received less attention, although it is of key importance for estimating the scale and consequences of landslides. The present paper explores numerically and analytically arrest of shear band propagation as well as global slab failure above the shear band. The complete evolution of a submarine landslide from shear band initiation, propagation, slab failure and arrest of SBP is observed through large deformation finite element (LDFE) modelling. Governing equations for both dynamic and quasi-static shear band propagation are established and solved, with results showing good agreement with the LDFE results. Lower limits for the final shear band length and for global slab failure are proposed for cases with high strain rate dependency of shear strength, where shear band propagation is quasi-static; upper limits are proposed for cases without rate effects where the behaviour is dynamic.