The Lee Tunnel in London has won the Concrete Society’s Award for Excellence in Concrete, the first tunnel project to ever win the award. The project, built by MVB JV (Morgan Sindall/Vinci Grands Projets and Bachy Soletanche), comprises five shafts, with the diaphragm walls the deepest recently undertaken in the UK at 90 m. A 7-m diameter, 7 km-long tunnel connects the shafts.
The innovative Dramix 5D steel fiber reinforced concrete (SFRC) for the slip formed tunnel lining took 18 months to develop, resulting in the use of a steel fiber reinforced self-compacting concrete. The five shafts were also designed and constructed using an innovative slip formed type of shaft construction, which also incorporated steel fiber reinforced concrete that reduced substantially the quantity of structural reinforcement, thus enabling a faster and safer construction process.
The Dramix 5D steel fibers provided excellent bending hardening properties to the concrete section, thanks to the high ductility wire, ultra-high tensile strength and perfectly shaped hooks. The designer (UnPS) and MVB JV decided to replace the traditional reinforcement with steel fibers, about 17,000 tons of rebar was replaced with more than 2000 tons of the Dramix 5D steel fibers. In this way they eliminated the very large and difficult logistical challenge that would have been placed before the contractors’ underground team.
The Dramix 5D series provides designers with new opportunities to design steel fiber concrete structures for both underground and surface works and enables contractors to build faster and safer solutions.
Peter Remory, General Manager of Bekaert Maccaferri Underground Solutions: “We are grateful we were a contributor to this award winning project. Thanks to the innovative fiber solutions we offer and our experienced team we were able to bring added value to the project and its stakeholders. The use of the newly developed Dramix 5D steel fibers opens up more reinforcement possibilities and allows higher productivity, it is also more cost effective and offers enhanced durability.”
The Society Awards judging panel said, “The Lee Tunnel was the most outstanding structure and therefore outright winner for its technical achievements in the use of concrete, its demanding placement conditions and innovative structural solutions. The statistics for concrete volume placed are impressive; the innovation required and final execution is exemplary. This project pushed the technical boundaries of what is possible with concrete.”
Richard Kershaw of CEMEX UK Materials, concrete supplier to the project, said, “We are very honoured to receive such acclaim from this most prestigious of awards. Concrete was the only realistic material choice for this structure. CEMEX is proud to be part of this momentous scheme and be part of a legacy to London, which will help prevent 16 million tonnes of sewage entering the River Lee and Thames each year.”