The paper summarises recent developments in the shear band propagation approach, which enables simplified submarine slope stability analysis to account for catastrophic and progressive failure. This approach covers a wide variety of potential failure mechanisms, such as slab failures, spreadings, ploughings and run-outs, and provides analytical energy balance criteria for predicting their occurrence. The simple form of the resulting criteria enabled their incorporation into deterministic and probabilistic slope stability analysis of offshore developments within the geographical information system. In contrast to conventional limiting equilibrium approaches used in such analysis, the shear band propagation approach is capable of explaining enormous dimensions of observed palaeo-landslides and predicting annual probabilities of failure that are orders of magnitude higher, as validated by reconstructed historical frequencies.

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.

The paper applies the energy balance kinematic method of plasticity theory to the large deformation problem of initiation and propagation of the spreading and ploughing failure outside a failed slab in submarine sediments. The models account for the phenomenon of the progressive propagation of a slope parallel slip surface, which is also quantified using the energy balance approach. In contrast to existing approximate analytical and numerical solutions, the proposed approach provides a theoretical basis for spreading and ploughing criteria as well as the comprehensive dynamic solution of the problem of post-failure landslide evolution. Incremental integration of the derived analytical expressions for kinetic energy in time allows for modelling recurrent initiation of new kinematic failure mechanisms with their subsequent large-scale deformation. Treating the failed slab as well as the spreading and ploughing mechanisms as one composite dynamically evolving mass movement allows for the final post-failure geomorphology of the failed slope to be predicted using basic mechanical principles.

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.

The problem of the limiting landslide pressure on an obstacle was first formulated in 1944 by Robert Haefeli of ETH Zurich, who recognised that the kinematics of the problem does not allow for classical active and passive earth pressure theories to be applied. He derived an approximate solution using a limit equilibrium approach with a number of rather arbitrary assumptions and simplifications. Since then, the Haefeli solution has been widely applied for the design and analysis of landslide retaining structures. The paper revisits this old landslide pressure problem by means of a rigorous upper- and lower-bound limit analysis and derives the exact landslide pressure solution for a planar landslide with a weak slip surface parallel to the slope. Being applicable to a wide range of natural and man-made obstacles and, unlike the classical theories, not affected by the wall friction and soil dilation, the upper-bound solution is rather robust. The landslide pressures from this solution increase with the strength of the sliding layer and are significantly higher than the active, but much lower than the passive, earth pressures. Of even higher practical importance, however, is that due to their oversimplifying assumptions, the widely used approximate solutions appear to get close to the exact solution only over a very narrow range of slope and friction angles. It appears that for mildly inclined weak slip surfaces and high strengths of the sliding layer, analysis and design of retaining structures based on well-known approximate solutions can become dramatically unsafe.