UK: Ground engineering complete for Silvertown Tunnel

Due for completion in 2025, the Silvertown Tunnel will be a 1.4km twin-bore road tunnel running under the River Thames, connecting Silvertown to the Greenwich Peninsula. The additional route is set to ease chronic congestion at the Blackwall Tunnel and enable more cross-river bus journeys.

Working on behalf of the Riverlinx CJV (a joint venture comprising Ferrovial Construction, BAM Nuttall and SK ecoplant), Bachy Soletanche delivered the geotechnical works for the Greenwich side of the River Thames, which took just under two years to complete.

For the tunnel’s South Portal, Bachy Soletanche installed rotary bored piles to form a secant wall, soldier piles and jet grouted columns. The company installed further secant piles for the Open Cut and Overbridge.

Another major section of the contract involved the construction of a diaphragm wall shaft to form the Greenwich Rotation Chamber, which enabled the reception and rotation of the TBM (tunnel boring machine) after it completed its southbound drive of the tunnel. To facilitate the safe manoeuvring of the TBM, Bachy Soletanche installed unreinforced CFA piles outside the shaft to strengthen and reduce the permeability of the river terrace deposits.

Further to this, Bachy Soletanche installed CFA piles for the Millennium Way Temporary Bridge, the Control Building, a new footbridge and several gantries, as well as cased CFA piles for the Open Cut Temporary Utilities Bridge.

At its peak, the demanding programme required 24-hour working and saw five rigs operating simultaneously.

Bachy Soletanche’s operations manager, Martin Stanley, commented, “Thanks to our team’s multi-disciplinary skill set and experience, we were able to respond well to the evolving programme and technical requirements throughout the project. Our experience of working in joint venture partnerships on other major infrastructure schemes in London, such as the Thames Tideway Tunnel and Crossrail, was essential in allowing us to support Riverlinx with specialist requirements, such as acquiring consents.”

Innovation

Throughout the programme, the site team received dedicated support from Bachy Soletanche’s Plant Department, who designed and manufactured a mechanical casing recovery tool, which can safely retrieve lost segmental casing from a borehole. In 2021, the innovation was shortlisted for two Ground Engineering Awards and won the Special Jury Prize in the VINCI Environment Awards.

Carbon reduction

Along with this, Bachy Soletanche helped to reduce the environmental impact of the scheme by monitoring fuel usage throughout the entire project and integrating electric pumps and equipment into its bentonite farms. The company also worked with its suppliers to procure grout and concrete mixes with as little embodied carbon as possible.

Value engineering

During a period of early contractor involvement, Bachy Soletanche’s in-house design team was responsible for proposing the Rotation Chamber’s diaphragm wall – an alternative solution to the originally specified secant piled wall. Working closely with the Riverlinx CJV, Bachy Soletanche’s design team also produced the geometric layouts for the ground treatment, as well as the soft concrete and grout mixes.