Basin Sediments Geometry and Strength as Controls for Post‐Failure Emplacement Style of Alpine Sub‐Lacustrine Landslides

Abstract

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.

A GIS framework for prediction of basin‐wide post‐failure geometry of confined subaqueous landslides

“…53 The Zinnen Slide area shows thinner and stronger sediments on the slopes compared to those in the basin (Figure 12B,D), which contributed the Zinnen Slide to fail in a frontally confined manner. 32 The sediments' strength increases linearly with depth and the strength of the weak layer was found to be a fraction of the strength (denoted as 𝑓 𝑤𝑙 ) of the overlying sliding sediments. Table 4 lists additional parameters required for the current study (more details in Klein et al 32 ).…”

“…This way, the problems related to mesh distortion associated with standard Lagrangian finite element analysis are minimized. The CEL method was applied in various studies to model similar problems and in back analysis of past slides, for example, Dey et al, 30,48 Stöcklin et al, 31 Klein and Puzrin, 19 Zhang et al, 28 Klein et al 32 Similar to DIFEM, the slide is triggered using a pseudo-static horizontal acceleration applied over 1 s, after which the slide becomes self-driven by gravity only. More elaborate details of the modeling technique can be found in Trapper et al, 49 Stöcklin et al, 31 Klein and Puzrin 19 and Klein et al 32 Figure 10 shows the post-failure slide geometry and the distribution of equivalent plastic strains as obtained by the ABAQUS model.…”

“…The Zinnen Slide pre-failure geometry (Figure 15) was derived by creating a cross-section along the seismic line in Figure 12C (section A in Figure 14). The thicknesses of the sediments on the slope and in the basin were interpreted based on seismic reflection profiles by Sammartini et al 53 (more details in Klein et al 32 ). Figure 15 shows the variation in strength profiles of the slope and basin sediments derived based on CPT results and FEM analysis.…”

“…Figure 15 shows the variation in strength profiles of the slope and basin sediments derived based on CPT results and FEM analysis. 32 The geometry and strength input parameters were used to run DIFEM calculation of the Zinnen Slide and the results, in terms of postslide geometry, were compared with CEL-FEM analysis and the interpretation of seismic reflection profiles. 32,53 Figure 16 F I G U R E 1 4 Failure initiation (primary failure) zone (𝑟 ≥ 1) and propagation (secondary failure) zone (0 ≤ 𝑟 < 1) of the southeastern banks of the Küssnacht Basin.…”

“…22 Over the years, a considerable amount of work has been devoted to the understanding of these mechanisms and the estimation of their potential dimensions. Among the methods used were analytical energy-based criteria 20,[23][24][25][26] and limit equilibrium [27][28][29] and various numerical methods such as large deformation finite element analysis, 28,[30][31][32] material point method, 33,34 smooth particle hydrodynamics, 35 particle finite element method, 36 depth-integrated methods [37][38][39][40][41][42] and more.…”