Impact of initial slide on downslope seafloor with a weak layer

Submarine landslides are a major offshore geohazard posing increasing threat to offshore and coastal developments. A submarine landslide may usually involve multistage failure triggered by the first failure. During submarine landslide evolution, the emergent sliding mass may act as an impact load on the downslope seafloor potentially leading to surficial erosion of sediments or deeper ploughing failure with the presence of a weak layer. The study presents a comprehensive analysis of seafloor instability and post-failure behaviors subjected to the first slide mass impact, using a large deformation finite element (LDFE) method. Different failure patterns are investigated and the corresponding critical impact loads for triggering the seafloor instability are analyzed. The parameters controlling the strain softening behaviors of soils and the undrained shear strength in the weak layer have significant effects on the critical condition for the seafloor failure. The dynamic inertia of the slide mass, however, has little effect on the results. An empirical equation for assessing the seafloor instability subjected to the first slide impact, with respect to the impact load from the initial slide and the gravity stress relative to the shear strength in the weak layer, is proposed based on a parametric study.