Submarine Landslides and the Impact Forces on Offshore Foundations

Abstract

This paper-based PhD thesis highlights the research on submarine landslides conducted in conjunction with the NPRA megaproject “Ferry Free E39,” which aims to replace ferry crossings with bridges and tunnels along a 1100 km coastal highway route from Kristiansand to Trondheim in the Western part of Norway. This research focuses on the 5 km Bjørnafjorden crossing, where a floating bridge anchored to the seabed is planned. Geophysical surveys have identified significant submarine landslide activity. Soft soil deposits are present at the flanks, which makes the impact scenario from potential submarine landslides a key challenge in the design of the bridge and the anchors. To address these geohazard risks, this research combines physical model testing and numerical simulations. The experimental studies investigated complete submarine landslide events, including an impact scenario with a foundation pillar. In addition, an experimental study on erosion of clays were undertaken. The results from the experimental studies include normalized impact forces on a foundation pillar and erosion rates for clays subjected to large flow velocities. Numerical simulations were conducted using the newly developed coupled Material Point Method with Computational Fluid Dynamics (MPM-CFD). The MPM-CFD method was validated from both previously characterized submarine landslide events at Bjørnafjorden and the performed model test experiments. The numerical simulations successfully replicated the results under both conditions. Consequently, the capability of the model to make class-A predictions makes it as a highly promising framework for predicting future submarine landslide events. The findings from this PhD study contribute to a more detailed understanding of submarine landslides and the assessment of potential impact forces on offshore infrastructures.