Burial Sledge System III

Subsea cables are installed by cable-laying vessels that carry the submarine cable on board. Dedicated tools excavate a trench in the seabed and bury the cable inside the trench. TME was contracted by Boskalis for the design and engineering of a burial sledge system for this purpose.

THE BSS III consists of a towed sledge vehicle, moving on skids over the sea bed, with a telescopically adjustable jetting lance for fluidizing soft sands and clays in front of the lance by water jets. Harder clays call for the mechanical chain cutter which reaches burial depths up to eight meters. A world first in cable burial!

Large forces are exerted on the lance when curving in hard soil. To prevent mechanical overload, the lance is mounted on the sledge using a flexible, hinge-like construction which acts as a mechanical buffer. To complement the mechanical buffer function of the hinge construction, an improved load measuring system featuring tensile-compressive load cells was integrated in the lance design to assure the correct measurement of critical loads and to enable timely intervention.

The weight of the structure was another design challenge that was successfully addressed. The limited bearing capacity of the seabed made it necessary to design a lightweight structure.

The weight challenge was cleverly addressed by keeping the skids detached from the primary lance support system. The primary lance support system endures large loads and hence requires a design that provides sufficient strength. Keeping the skids detached from the primary lance support system, enables a compact, lightweight skid design.

Given the weight target and the need for predictable mechanical behavior of the construction, welding connections were replaced by pin-hole connections exhibiting pure tensile-compressive behavior. These well-defined connections enabled a reliable lightweight construction.

The demanding requirements and associated high-risk profile of this project demanded close collaboration with our customer and fully-fledged engineering.

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