A Herrenknecht EPB Shield machine named Jill presented two exciting challenges for the tunnelling team in London in 2022-2023: The compact launch shaft required a ‘flying launch’ due to the special ring design. Additionally, the miners had to rotate the machine by 180 degrees. This project involves the construction of the 1.4 km long double-tube Silvertown Tunnel under the Thames in east London.
London is addressing chronic congestion in the Blackwall Tunnel by constructing the Silvertown Tunnel in the east, the first new underground road link across the Thames in 30 years. Stretching 1.4 kilometres, the tunnel accommodates two lanes on each side. The TBM, nicknamed “Jill,” provided by Herrenknecht, is the UK’s largest, with a nearly 12-meter shield diameter, weighing 1,800 tonnes, and spanning 82 meters. By the time work was completed on July 23, 2023, “Jill” had installed 1,120 segmental tunnel lining rings, each weighing around 70 tonnes. Riverlinx CJV, the contracting joint venture, achieved exceptionally precise tunnelling within less than a year. The breakthrough for the southbound tunnel occurred as early as mid-February 2023.
Turning a 1,450 tonne machine by 180 degree
When constructing twin-tube tunnels, typically two TBMs are used or a single TBM is returned to the launch site for the second drive. However, due to complex factors such as construction technology, time, and finances, project managers chose a unique approach for the Silvertown Tunnel. After completing the first tunnel, the entire machine was rotated 180 degrees to bore the northbound tunnel. This involved excavating an 18-meter deep, 40-meter long shaft. Herrenknecht specialists executed the 180-degree turn of the 1,450-tonne shield machine in London within a single day.
Bringing Jill on track for a scheduled drive
For us at VMT, the main challenge was the big TBM in a relatively small starting shaft. We are proud of the great work by the surveyors measuring the starting position of the TBM and of all VMT equipment having worked reliably during the project:
- Guidance system with SLuM (Automatic Tailskin Clearance)
- RCMS (Ring Convergence) and Moving Station
- Segment production support with SDS onsite and LIS services during production
Further, the contractor used a special ring design with left and right tapering. It was not allowed to put the key stone between 90° – 270°. To meet this requirement, the team mastered the starting situation with the flying launch to bring the ‘big girl’ on track.