Construction – Landfall

Overview

The key engineering process critical to the “trenchless installation” of these ducts was Horizontal Directional Drilling. The ducts are made of 450mm high-density polyethylene pipe, welded together to form a continuous length.

Offshore, both cable ducts emerge in two excavated exit pits, to ensure both pipe and cables are below the seabed when construction is completed. The ducts remain sealed to prevent seawater and debris from entering the pipes, until the two 220kV HV export cables are installed in 2020.

All nearshore HDDs and the supporting onshore construction activity takes place from Temporary Construction Compound 1*.

Principle Contractors:

  • VBNK consortium (Boskalis with cable manufacturer NKT) - Nearshore HDD installation.
  • J Murphy & Sons Ltd (JMS) - Onshore Cable route and civils. 

Expected completion: Q3/Q4 2020 (completion of landfall works and reinstatement.)

 

* Temporary Construction Compounds are key hubs located alongside main construction works and used for the likes of materials storage, facilities and equipment.

 

Progress updates

The site was handed back to our onshore cable contractor, J Murphy & Sons (Murphy), in September 2019 and work has been continuing around the construction compound ever since.

All of the Horizontal Directional Drilling and duct installation is now complete around the construction compound.

Murphy continue with works on site at the compound in preparation for the construction of the Transition Joint Bay (TJB) (where the offshore cables and onshore cables will join).

During October, stone taken from other locations along the onshore cable route which have already been reinstated, was delivered to site using the dedicated access road. The stone is due to be used at the location of the TJB, as the ground requires raising to enable Murphy to construct the bay.

The actual footprint of the compound is being reduced, as the remaining works require less storage and plant than the offshore drilling works which are already complete.

We expect the TJB construction works to complete by the end of November 2019. Smaller ‘enabling works’ will then continue periodically until the site is handed back to our offshore cable contractor, Boskalis, in Q2 2020 in order to complete the offshore cable installation works. We expect these works to take place over Q2 and Q3 2020.

Once installed, the cables will require testing and then restoration works will commence. We expect the site to be fully restored by the end of November 2020.

The preparation phase at the cable landfall site ended in July 2019, with the two 900m long Horizontal Directional drills and duct installations complete, ensuring the site is now ready to receive the offshore export cable when it is installed in Q2 2020.

Demobilisation of the HDD equipment and personnel from the onshore temporary site continued until the end of July and was cleared by the beginning of this month (August 2019.)

This latest milestone comes with a “thank you” message from the project to the neighbouring communities, for their support and patience during the 24hrs drilling works.

In advance of the works, we held an open day for local residents to explain the works and keep the community up to speed with our works. Responding to requests from the parish council and members of the public, our contactor Boskalis took significant steps to ensure the works would have minimal impacts on the use of the beach, and has used new, high-tech sound suppressing techniques and protection to reduce noise impacts.

The site is due to be handed back to J Murphy & Sons who will continue with the onshore cable works in  September 2019.

The key works to connect Triton Knoll’s onshore and offshore electrical circuits start this Spring at the project’s landfall location north of Anderby Creek.

To date, JMS has been preparing the onshore Haul Road which runs between Temporary Construction Compound* (TCC) 1 and 2, and includes the building of a bridge across Anderby Main Drain, to allow construction traffic to access TCC 1.

The nearshore Horizontal Directional Drilling and supporting onshore construction activity will take place from TCC 1. The drills will establish two 900 metre-long tunnels beneath the sand dunes and beach, avoiding the sea defences. These tunnels will emerge offshore in two purpose-built exit pits; specialist vessels will then feed the high-density polyethylene pipe ducting through from offshore to onshore, ready to receive the 220kV export cable circuits later in 2020.

In anticipation of potential low-level noise associated with the works, both directly from the drilling and from the supporting infrastructure, our contractors worked hard to minimise this, including installing soundproofing and using low noise equipment where they were able.

All works are coordinated with the Environment Agency to avoid impacting on the annual beach replenishment programme in the Spring.

Throughout the works, visitors to the beach will see a number of vessels close to shore, including a BackHoe Dredger and a Pipe Feed-in Barge, as well as numerous smaller vessels linked to the works.