Geohazard Assessment for a Submarine Cable

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This paper describes a geohazard study for a submarine cable passing through fjords with challenging soil conditions and highly variable bathymetry. The main geohazards evaluated included slope stability along the cable corridor and rockfall triggered by earthquakes. One-dimensional static, pseudo-static and displacement analyses along the cable corridor were performed to identify critical locations. For the identified critical zones, static and pseudo-static 2D slope stability analyses using a finite element program and an advanced constitutive model to account for soil anisotropy were conducted. Mitigation measures suggested for slopes with low static factors of safety included rock dumping, trenching, and micro-routing. For low probability earthquake events, contingency planning for rapid inspection and repair post-event was recommended. For the submarine rockfall hazard assessment, runout distances of single blocks were estimated using physics-based analytical solutions. A sensitivity study was performed on key parameters to assess uncertainty. The results showed that the probability for rockfalls to reach the power cable is high for two of the studied locations. However, there were no clear indications of deposited rockfall blocks at the two critical locations. Therefore, the overall likelihood of rockfall impacting the cable is low, given the low probability of rockfall initiation. This assessment ensures the safe and reliable design and installation of a subsea cable, mitigating potential geotechnical risks and informing necessary mitigation measures to protect it against geohazards. The work presented here demonstrates the need for comprehensive and multidisciplinary geohazard analyses for offshore infrastructure projects.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

1 - Site investigation strategies, geohazards and integrated studies