The TBM breakthrough has been made on National Grid’s Grain to Tilbury project, completing the drive under the River Thames.
The 2.2km tunnel – part of The Great Grid Upgrade – will house a high-voltage electricity cable between Tilbury in Essex and Gravesend in Kent.
On September 27 Herrenknecht TBM Caroline completed the final stage of her journey underwater. The reception shaft was flooded to balance pressure between the shaft and surrounding chalk ground and reduce the risk of groundwater entering the shaft during the final stage of tunnelling.
National Grid says its delivery partner, Ferrovial BEMO JV, completed the drive 49 days ahead of the original programme following an exceptional tunnelling performance.
The company says planning, favourable ground conditions, and the proven performance of the TBM contributed to the early breakthrough, alongside well-coordinated logistics that kept tunnel segments continuously delivered to the TBM, while a dedicated separation plant processed excavated material efficiently.
More than 10,000 concrete tunnel segments were installed to create the tunnel lining, and nearly 1,700 tunnel rings constructed.
In the most productive month, the mixshield TBM advanced 926m and installed 712 tunnel lining rings. At peak performance, the machine advanced 229m in a single week, while its best daily output was 41m excavated and 31 tunnel rings installed in 24 hours.
Digital design tools and connected TBM data also supported delivery by improving visibility, quality assurance and decision-making. An integrated underwater telescopic camera allowed inspections to be carried out remotely, reducing the need for personnel intervention.
TBM Caroline will now advance beyond the shaft wall to enable the remaining ring-segment construction works to be completed.
Dewatering of the shaft started in September and will continue through October.
National Grid project director Mark Farmer saidthe TBM breakthrough wasa major milestone for the Grain to Tilbury project.
“Completing this tunnel drive ahead of schedule is a testament to the expertise, dedication and collaboration of our teams and supply chain partners. Everyone involved has worked together to deliver an exceptional performance safely and efficiently, helping us reach this important milestone sooner than anticipated,” he said.
“This project will play a critical role in strengthening the electricity network and supporting Britain’s future energy needs as demand for cleaner electricity continues to grow.”
Ferrovial BEMO JV project director Borja Trashorras said achieving the breakthroughahead of schedule was the result of excellent planning, strong engineering expertise and collaboration across the project team.
“The combination of diligent planning, efficient logistics, innovative tunnelling technology and a highly skilled workforce enabled us to achieve consistently strong performance throughout the drive. We are extremely proud of this achievement and of everyone who contributed to making it possible,” he said.
