SSEN Relies on HDD for £9.6 Million M27 Project

Using horizontal directional drilling (HDD), a vital new cable has been installed beneath the M27 motorway, one of the busiest in the south of England.

The work is part of a £9.6 million (USD 12.7 million) investment by Scottish & Southern Electricity Networks (SSEN) and is currently under way in Hampshire.

Project Approach

Working with its contracting partners at Freedom, SSEN carefully designed the project to improve the local electricity infrastructure while minimising disruption and protecting the environment, delivering long-term benefits.

Instead of laying new power cables across the motorway, which would have caused delays for drivers, the team developed an innovative solution to place the cables well below the road surface. To avoid unnecessary disruption to motorway traffic and reduce the impact of construction on the local environment and wildlife, a more complex underground approach via HDD was adopted.

Technical Details

The horizontal directional drilling crossing on the Rownhams project is approximately 260 metres long. National Highways requires the bore to be carried out at least 15.8 metres beneath the carriageway.

There is no standard for this in our country either; although the General Directorate of Highways requires a minimum depth of 3 metres below the road axis, there is no real standard. Moreover — for a reason we have never been able to understand — road crossings by directional drilling are required to be exactly perpendicular to the road axis.

Because of the nature of the area and the position of the road, the actual depth of the bore reaches 45 metres below the starting point, at what is known as the “entry face”.

During drilling, a non-toxic, naturally sourced clay-and-water mixture (bentonite-based drilling fluid) is used to keep the bore clean, prevent collapse and remove the cuttings.

Statement from Project Manager Tim Eccleston

“This multi-million-pound investment is to future-proof the network and also allow nearby Rownhams to install more electric-vehicle charging points. Located on one of the busiest motorways in the south, this site is vital in allowing drivers to charge their EVs at an important point in their journeys. But the location also created a challenge in how we could deliver this improvement without further disrupting roadworks and traffic on the motorway. Our commitment was to make sure this project was designed appropriately for customers, road users and the environment, and by re-routing the cable beneath the M27 we were able to deliver on that commitment.”

Benefits of the Project

The £9.6 million programme is still under way; when complete, it will supply electricity to local customers while supporting the installation of new electric-vehicle charging points on an important section of the UK road network.

In its statement SSEN said that its approach to the project shows how electricity infrastructure can be delivered in a smarter and more thoughtful way, while strengthening the grid, supporting the transition to electric vehicles and keeping people moving on one of the busiest motorways in the south of England.