Construction – Onshore cable route

Overview

Full construction of the onshore cable route began in September 2018 combining trenched excavations, the installation of ducting and Horizontal Directional Drilling (HDD). HDDs are critical to installation, ensuring we avoid obstacles like roads and watercourses. There are over 700 HDDs being installed at 147 separate drilling locations along the route, and which we believed is the most recorded for an infrastructure project of this kind in the UK.

Principle Contractor: J Murphy & Sons Ltd (JMS)

Expected completion: Mid-2020

Progress updates

The project is rapidly approaching the winter months and so is gearing up for the weather impacts that this time of year can bring.

Throughout late summer and early autumn, the project made fantastic progress including the successfully completion of one of the more complex  Horizontal Directional Drill (HDD) on the project, at the River Witham.

The river is one of the region’s primary drainage waterways, stretching over 130 kilometres across Lincolnshire and is in parts over 90 metres wide. A highly specialised HDD was required, of around 264 metres in length and to a  depth of around 16 metres, through very difficult ground conditions

  • Take a look at our short film, below, to see how Triton Knoll met this engineering challenge.

With the success of the Witham, the project has completed over 99% of the individual HDDs required on the project, with a small number of drills to complete at some key locations along the route  To date, specialist teams have successfully installed  of over 79,300metres of HDD ducts, including over 740 individual HDD drill shots.

Installation of protective plastic cable ducting has progressed well and is now 99% complete, with the final sections ready to be installed once the HDD works are complete.

So far, almost 50% of High Voltage Alternating Current (HVAC) onshore cable has been installed, and over 20% of the cable joints completed, with the works continuing on target and according to programme.

Throughout, one of the project’s most significant challenges has been to minimise construction impacts on the region’s agricultural heartland.

Martin Knagg, onshore cables package manager explained: “We are absolutely delighted to have already reinstated around 10% of the land used in the cable route which formally began just 12 months ago. This has been very well received by the landowners involved, and the land is already being re-ploughed for the first winter crops to be planted.”

The project will continue reinstatement work in early spring after the less favourable winter weather.

Over 97% of the individual Horizontal Directional Drills (HDDs) required on the project have now been completed. There are 147 separate drill locations each requiring up to six separate drills to accommodate the two circuits of three HVAC cables.

One of the largest HDDs on the project is below the River Witham, stretching around 264 metres in length and to a maximum depth of around 16.35 metres, and installed from August to October 2019.

Installation of the protective plastic cable ducts continues to progress well and is now 90% complete. Weather permitting, cable duct installation along the full cable route is scheduled to be completed by the end of September.

Deliveries of High Voltage Alternating Current (HVAC) onshore cable began in Spring 2019, when drums of between 1,023metres and 1,690metres of HVAC cable arrived at Port of Boston. The deliveries will remain on going until the end of the year.

In July 2019, we installed the first lengths of onshore HVAC cable into the cable ducting, ready to transport power from the offshore turbines into the national grid network and ultimately UK homes and businesses. Since then, we have already completed the installation of over 30% of the onshore cables.

The electrical cable installation is taking place across one large work front which will split into two work fronts towards the end of September, with one working toward the Siemens sub-station in phase 2 and the other working towards the Transition Joint Bay (TJB) at the beach in phase 1.

Finally, thanks to the progress already made, we have been able to begin some of the reinstatement works along the cable route, less than 12 months after beginning onshore construction.