A tunnel boring machine (TBM) has reached the halfway point in the construction of a new 2.2km high-voltage electricity cable tunnel between Tilbury in Essex and Gravesend in Kent.
Since starting its journey in May, TBM Caroline has excavated more than 40,000t of material and installed over 5,100 pre-cast concrete tunnel segments to form the tunnel lining using a specialist Mixshield system.
The TBM, named after pioneering electrical engineer Caroline Haslett, weighs 464t, including its trailing gear.
The National Grid’s Grain to Tilbury project will replace the Thames Cable Tunnel, which was originally built in 1969 and is approaching the end of its operational life. The project’s main contractor is a Ferrovial and Bemo joint venture under a £230M contract. They are working in collaboration with German tunnelling specialist Herrenknecht.
The Grain to Tilbury project will also involve the construction of two headhouses at either end of the tunnel, which will facilitate access to the system. Additionally, cable sealing end compounds will be created to integrate the new underground cable with the larger electricity network.
Completion is expected by 2029.
Mark Farmer, project director at National Grid, said: “Reaching the halfway point of tunnelling beneath the River Thames is an important moment for the Grain to Tilbury project and is a testament to the expertise and collaboration of teams across National Grid and our partners.
“The progress made so far reflects the dedication of everyone involved and moves us a step closer to delivering infrastructure that will help strengthen the electricity network and support Britain’s future energy needs.”
Borja Trashorras, project director at Ferrovial Bemo JV, said: “Delivering more than 1.1km of tunnel safely through complex ground conditions, while maintaining strong productivity and environmental performance, is a testament to the planning, engineering and innovation at the heart of this project. We’re proud of the progress made so far and remain focused on carrying that momentum forward as Caroline continues her journey towards a breakthrough later this year.”
Ulrich Schaffhauser, member of the board of Herrenknecht, said: “National Grid’s Grain to Tilbury project is a benchmark project in every respect. It is impressive to see what can be achieved when tailor-made technology and professional project execution come together.”
TBM Caroline’s milestone follows a series of major achievements on the project, including the launch of ‘Verena’, Europe’s largest-diameter vertical shaft sinking machine, which was used to construct the tunnel access shafts at Tilbury and Gravesend.