Subaqueous slope failures can evolve in various patterns. Whereas some slides run out and further evolve into highly mobile turbidity currents, others maintain a continuum-like structure and remain frontally confined. The different failure modes impose different hazard scenarios, making an understanding of their origin crucial for reliable hazard assessments. Yet many of the factors controlling their post-failure behaviour remain not well understood. In this paper, a procedure is presented for the analysis of the post-failure evolution of subaqueous landslides, using a coupled Eulerian–Lagrangian finite-element analysis approach. The procedure is applied to analyse the St Niklausen slide in Lake Lucerne (Switzerland), providing a good prediction of observed landslide features, without back-calibration of input parameters. The approach is further applied to investigate the influence of controlling parameters, highlighting effects of different strength parameters, the surrounding water and the slope stratigraphy and geometry on the landslide dynamics. The procedure presented can be generally applied to predict the post-failure evolution of subaqueous landslides and facilitates the extraction of the moving soil–water boundary, which can serve as source input for tsunami propagation modelling.

The volume of submarine landslides is a key controlling factor for their damage potential. Particularly large landslides are found in active sedimentary regions. However, the mechanism controlling their volume, and in particular their thickness, remains unclear. Here we present a mechanism that explains how rapid sedimentation can lead to localized slope failure at a preferential depth and set the conditions for the emergence of large‐scale slope‐parallel landslides. We account for the contractive shearing behavior of the sediments, which locally accelerates the development of overpressures in the pore fluid, even on very mild slopes. When applied to the Santa Barbara basin, the mechanism offers an explanation for the regional variation in landslide thickness and their sedimentation‐controlled recurrence. Although earthquakes are the most likely trigger for these mass movements, our results suggest that the sedimentation process controls the geometry of their source region. The mechanism introduced here is generally applicable and can provide initial conditions for subsequent landslide triggering, runout, and tsunami‐source analyses in sedimentary regions.

Predicting the evolution of underwater mass movements in their post‐failure stage is vital for risk assessment of offshore structures and ensuring safety of coastal communities threatened by tsunami waves. In the absence of sedimentological and geotechnical data, variability of the post‐failure behavior in a specific marine or lacustrine setting is often attributed to predisposition factors such as the slope height‐drop and depth to the basal shear surface. In this paper, the contribution of other geometrical parameters such as the slope inclination and the relative thickness of the frontal basin sediments is investigated using a coupled Eulerian‐Lagrangian finite element framework. An emphasis is given to the important role of the strength difference between the slope and frontal basin sediments. The suggested framework is first validated against the well‐documented Zinnen slide in Lake Lucerne (Switzerland), successfully reproducing the post‐failure geometry and capturing the main features observed in published seismic profiles. It is then applied in a parametric study to illustrate the decisive role of the frontal basin sediments in determining the post‐failure geometry of underwater mass wasting in similar settings.

Landslides are often triggered by earthquakes and can cause immense damage due to large mass movements. To model such large-deformation events, the material point method (MPM) has become increasingly popular in recent years. A limitation of existing MPM implementations is the lack of appropriate boundary conditions to perform seismic response analysis of slopes. In this article, an extension to the basic MPM framework is proposed for simulating the seismic triggering and subsequent collapse of slopes within a single analysis step. Original implementations of a compliant base boundary and free-field boundary conditions in the MPM framework are presented, enabling the application of input ground motions while accounting for the absorption of outgoing waves and the free-ground movement at the lateral boundaries. An example slope is analysed to illustrate the proposed procedure and to benchmark it against the results obtained using an independent simulation technique, based on a three-step FE analysis. The comparison generally shows a good agreement of the results obtained from the two independent procedures and highlights advantages of the presented “all-in-one” MPM approach, in particular for long duration strong motions.

In dynamic geotechnical problems, soils are often subjected to a combination of sustained static and fast cyclic loading. Under such loading conditions, saturated and normally consolidated clays generally experience a build‐up of excess pore water pressure along with a degradation of stiffness and strength. If the strength of the soil falls below the static stress demand, a self‐driven failure is triggered. In this paper, a constitutive model is presented for the analysis of such problems, based on a general multisurface plasticity framework. The hardening behavior, the initial arrangement of the surfaces, and the nonassociated volumetric flow rule are defined to capture important aspects of cyclic clay behavior. This includes nonlinear hysteretic stress‐strain behavior, the effect of anisotropic consolidation, and the generation of excess pore water pressure during undrained cyclic loading along with a degradation of stiffness and strength. The model requires nine independent parameters, which can be derived from standard laboratory tests. A customized experimental program has been performed to validate the model performance. The model predictions show a good agreement with test results from monotonic and cyclic undrained triaxial tests, in particular with respect to the strain‐softening response and the number of loading cycles to failure. A procedure for a general stress‐space implicit numerical implementation for undrained, total stress‐based finite element analyses is presented, including the derivation of the consistent tangent operator. Finally, a simulation of the seismic response of a submarine slope is shown to illustrate a possible application of the presented model.