Scottish trenching and excavation specialist Rotech Subsea has completed work on pit clearing and cable lowering projects at the Borssele 1&2 and Triton Knoll offshore wind farms in the North Sea.

The company was contracted to provide its jet trenching tools to carry out three major scopes of work: pit clearing and cable lowering at the 752MW Borssele 1&2 in the Dutch North Sea, as well as grout bag and cable de-burial at the 860MW Triton Knoll in UK waters.

The work started during the first quarter of the year.

Phase one and two of the project saw the subsea trenching specialist provide its TRS1 tool for two pit clearing operations.

Rotech’s TRS1LD was also provided for phase three, which consisted of post-lay cable trenching to a specification of 3.0m DOL (depth of lowering), as well as cable de-burial.

Rotech Subsea director Stephen Cochrane said: “The bellmouth pit excavation was approximately 30m by 50m by 4m and we successfully kept the pit open despite 1.5m of sand migration every 12 hours. The cable lowering was completed with ease, too, with some sections requiring 4.5m DOL.”

Soil conditions varied at the Borssele 1&2 site ranging from sandy conditions near shore to harder soils further out to sea.

Approximately 100m of cable and grout bags were successfully de-buried, allowing the client to commence with cable removal operations.

Triton Knoll is now in construction, installing the onshore electrical system in Lincolnshire.

Installation of the offshore array and infrastructure began in January 2020, 20 miles off the coast of Lincolnshire.