Submarine power cables on soft structured clay seabed: gravel berm to reduce cable settlements and enhance protection

Submarine power cables on soft seabed are prone to damage from fishing gear, anchors, and underwater landslides. To mitigate these risks, the paper investigates the long-term settlement and stability of protective berms using PLAXIS finite element simulations. The paper examines two berm geometries, staged construction, and the influence of backfill pre-consolidation before berm placement. To compute settlements in structured clays, this study developed a novel iterative method within the finite element framework to adjust the modified compression index based on the soil destructuration. The approach identifies the steepest slope of the oedometric curve, indicating maximum clay destructuration, to estimate the critical modified compression index ((Formula presented) Subsequently, vertical stresses are monitored at various soil depths to define a new modified compression index. Finally, the value of the modified compression index is iteratively refined during simulations until reaching convergence. Additionally, for comparison, the paper presents calculations of a single case with the Creep-SCLAY1S model. Simulations calculated cable settlement and long-term stability, giving insights into berm geometry optimisation that can reduce settlement. Results demonstrate that defining the modified compression index according to stress conditions at various depths produces more realistic results than using a single value typically applied to non-structured soils.