The cable installer drilled two 1,170-metre long horizontal directional tunnels near Weybourne in north Norfolk on England's east coast, where the Dudgeon offshore project cables reach land.
Two pipes have also been installed to hold the project's export cables.
To avoid winter weather conditions, the work was brought forward by three months. The two 42km export cables will be installed from March next year.
Planned for a North Sea site 32km off Norfolk, the 402MW Dudgeon project is being jointly developed by Statoil, Statkraft and Masdar.
In April 2014, it was awarded a final investment decision-enabling CfD subsidy by the UK government. The contract guarantees a fixed price for the electricity produced over 15 years.
In May, the developers announced the project had reached a contractual milestone that is part of the subsidy requirement, by spending 10% of expected project costs, which included the contract with VBMS.