Cofferdams Assist FCC and EKFB ‘Thame Viaduct’ Project
Sheet Piling (UK) Ltd is playing its part in an HS2 viaduct project, described as “a game-changer for the industry”, by leading publication New Civil Engineer.
The project in question is the Thame Valley Viaduct, where Sheet Piling UK is undertaking work for FC Civils Solutions, working on behalf of EKFB, a joint venture of Eiffage, Kier, Ferrovial Construction and BAM Nuttall.
This is part of FCCS’s work for EKFB, on the C2 and C3 sections of the High-speed Rail (HS2) project and it is fair to say that the Thame Valley Viaduct work is making waves.
Contributing to FCC and EKFB’s project
Our contribution to FC Civils Solutions and EKFB’s vision at this site, which lies on the western periphery of Aylesbury, in Buckinghamshire, is the installation and extraction of 33 temporary steel sheet pile cofferdams, formed of top quality used sheet piles.
The 33 temporary cofferdams, each measuring 15.6m x 6m, are providing the foundations for the intermediate piers of the viaduct. The viaduct will be 880m (2890 feet) in length and will comprise 36 evenly-spaced spans.
Concrete piers will support this structure, which will only be three metres (9.8 feet) high, to help minimise the aesthetic impact on the surrounding landscape. Each pier will have two pier stems, both of which will rest on a pile cap. A novel approach is being adopted with regard to the beams, which will be pre-cast box girders that remove the need for a diaphragm. Two will be fitted per span.
Steel sheet pile cofferdams aid carbon-saving viaduct design
It has been said that the viaduct will be slotted together “like a giant Lego set”, with a modular design, and a methodology of off-site manufacturing and assembly of pre-fabricated sections, helping to save 19,000 tonnes of embedded carbon from the FCC and EKFB project.
The steel sheet pile cofferdams are an essential component of the viaduct construction process. Sheet Piling UK has been working with a maximum excavation depth of 5 metres, for each one and started installing the first in October 2022. Work will continue for 14 months, with each temporary cofferdam extracted, once the necessary pile cap foundation work has been completed. The extracted structure will then be reinstalled at the next pier foundation along, as work progresses.
Pre-auguring as part of safety-first approach
Installation is having to take place through a significant amount of made ground. This was specifically put in place ahead of sheet pile installation, to raise the piling platform above flooding level. Given the river location and the surrounding land, much of it wetland, this was a key consideration.
Whilst this has ensured greater safety, it does make it necessary to pre-augur the pile line. We are using a Kobelco SK380 SRLC excavator, fitted with an SG75 Side Grip Vibratory Hammer, for this purpose. All plant being used on this FCC and EKFB project is NRMM-compliant, in line with HS2 requirements.
The cofferdams are being stabilised through the use of temporary hydraulic bracing, supplied by RMD Kwikform.
Sustainable sheet piling
In total, Sheet Piling UK has supplied six sets of temporary used sheet piles, drawing these used piles from its extensive stock and demonstrating the advantages of steel sheet piles, in terms of strength and reusability. Given our commitment to working as sustainably as possible, the methodology used in this project ticks all of our boxes.
We are delighted to assist FC Civils Solutions and EKFB on this part of the HS2 network. The Thame Valley Viaduct has been designated a Key Design Element, because of its proximity to the local community and it is vital to ensure that it minimises its impacts on the resident population. Once complete, it will carry high speed trains across the River Thame and surrounding wetland, at speeds of up to 360 km/h. Trains will travel on routes between London, Birmingham and the North, helping to deliver economic benefits across the UK.
The Thame Valley Viaduct is one of 15 designed by HS2’s main works contractor, EKFB and their designer ASC (a joint venture between Arcadis Setec and COWI) and specialist architects Moxon.
To make an enquiry about sheet piling for rail infrastructure projects, please call us on 01772 794141.
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Sheet Piling (UK) Limited is one of the UK's leading piling contractors. Owning and operating a comprehensive range of specialist piling equipment Sheet Piling (UK) Ltd also carry extensive stocks of new and used piles enabling rapid reaction to any urgent requirements or emergency situations.