Catthorpe Interchange Project
Surrounded by rolling Leicestershire countryside, the motorway interchange – where the M1 meets the M6 and the A14 trunk road – near the village of Catthorpe is one of the busiest road junctions in the UK and is used by more than 150,000 motorists daily.
An eagerly awaited £191 million improvement scheme, that will benefit commuters and other road users with smoother, more reliable journeys on these key routes, was officially opened by Highways England last year. Integral to this major project was the skilled application of precast concrete units, produced by Bison Precast.
7,000m² of Omnia Bridge Deck concrete units, designed, manufactured and supplied by the team at Forterra Precast Concrete (now known as Bison Precast), were installed by Skanska UK as part of four brand new bridges at the three-level stack interchange. The installation work took place throughout 2016, during which time traffic continued to flow on all three routes.
The Omnia Bridge Deck system is a practical and efficient method of providing formwork to deck slabs of bridges, particularly in cases where bridges span live roads and railways. It has been officially recognised by the Department of Transport through its model specification for precast concrete bridge decking.
This system allows a bridge deck to be installed to provide a permanent framework for the in-situ concrete deck. C45/C55 concrete mixes were employed in this particular project. A steel reinforcement lattice was used to provide the requisite stiffness to the precast Bridge Deck unit for it to support the weight of wet concrete, and allowing a mechanical key between the precast unit and the in-situ concrete. For this project, Forterra’s Type 3 Deck was used, giving a minimum slab depth of 250mm, in which the lattice depth was 130mm. The Type 3 Deck provides a maximum clear span of 3,350m.
During the manufacturing process, the laitance is removed from the upper surface to provide the required shear interface between the precast and in-situ concrete.
The Bridge Deck units were designed to carry construction loading and limit deflections to span/400 and crack widths to 0.1mm. The lattice girders were aligned during manufacture to ensure ease of fixing longitudinal reinforcement over the Bridge Deck units.
The manufacturing tolerance and Type F2 soffit finish are as specified in Series 1700, Structural Concrete, Specification for Highway Works, as part of Standards for Highways.
The Omnia units were hoisted into place at the interchange site using Forterra’s QuickLift System, which improves onsite efficiency by lifting as many as eight bridge deck units at a time, reducing installation times by up to 20% compared to alternative methods.
As part of a successful installation, the units are butted together to close any gaps and minimise the risk of grout loss, and to reduce the risk of any cutting or make-ups due to creep. The precast units, which have a design life of 100 years, were supplied from Bison Precast’s Somercotes facility less than 60 miles from the site in neighbouring Derbyshire, keeping transport costs and the associated carbon footprint as low as possible.
The three-level junction was opened on March 16th, 2017, and now provides a direct dual carriageway link between the M6 and A14, together with free-flow links between the A14 westbound and M1 northbound, M1 southbound and A14 eastbound, M6 eastbound and M1 southbound, and M1 northbound and M6 westbound.
Martin Bolton, National Sales Manager for Bison Precast at Forterra, said, “We employed our considerable experience on major UK bridge projects to ensure the precast units for the interchange improvements at Catthorpe were engineered to the highest possible standard, for a completed project which will be used by tens of millions of vehicles every year.”
Mark Sutton, Construction Manager for Skanska UK, said: “The Omnia Bridge Deck System enabled the team to create a safe, reliable and consistent decking system in an efficient manner across the scheme.
“The team at Forterra were able to assist with the development of bespoke panels to suit the pinch point locations on the bridge deck which ensured a smooth continuation of installation.”
Highways England Chairman, Colin Matthews, said: “This project has been delivered on time and on budget and is a great achievement for our own team and our contractors.”