The stunning cable stayed multi-span bridge at the centre of the Mersey Gateway scheme is a real show-stopper.
But the elegant design of 2.13km long bridge with its 1km span over the River Mersey is not the only reason the project was named by KPMG as one of the top 100 global infrastructure projects. Comparing it to the Bosphorus Bridge in Turkey, the consultancy firm said the Mersey Gateway “offers an equally impressive and desperately needed solution, improving mobility and economic growth throughout the Liverpool city region, north Cheshire and the North West of the UK.”
Mersey Gateway is a network of 7km of new roads designed to relieve congestion on the Silver Jubilee Bridge between Runcorn and Widnes. That bridge – itself an iconic structure – opened in 1961, and was designed to carry 8,000 vehicles a day. But 50 years on, more than 80,000 vehicles were using it, and the surrounding road network just could not cope.
Plans to relieve this congestion with a second road crossing of the Mersey go back more than 20 years. Those plans promoted by local authority Halton Borough Council, along with neighbouring councils, agencies, business organisations and developers were thwarted many times, but eventually came to fruition in autumn this year, when the Mersey Gateway was opened to traffic. It has been built as a public-private partnership (PPP), with Halton Borough Council awarding the Merseylink consortium a contract to design, build, finance and operate it for 30 years. Merseylink is made up of Macquarie Capital, FCC Construcción and BBGI.
Merseylink CCJV, the consortium’s construction joint venture of FCC Construcción, Kier Infrastructure & Overseas and Samsung C&T Corporation, began work on site in 2014, to designs by a JV between Cowi (formerly Flint & Neill) and URS, now part of Aecom. The construction and land acquisition costs of around £600M, are split almost equally between the new bridge and the landside road improvements.
“The project is more than just a bridge,” says Merseylink CCJV construction director Juan Manuel Dochao, who describes Mersey Gateway as a “transformational project”.
“It is the catalyst that will connect communities and lead regeneration and investment throughout Halton and the North West. The iconic design of the bridge will put the local area, Liverpool and the North West region firmly on the map and will encourage attention from all over the world.”
He adds: “To deliver a project of such importance, a construction joint venture with an extensive track record for delivery across the globe was assembled. All three companies work in the global market: FCC has significant experience building large approach viaducts, Samsung has worked on many cable stay bridges, and Kier provided local knowledge and experience.”
We had more than 1,000 workers operating at the same time, in different places in such a challenging place
Juan Manuel Dochau, Merseylink CCJV
Dochao says one of the biggest challenges was coordinating this international construction team : “We had more than 1,000 workers operating at the same time,
in different places in such a challenging place, as well as dealing with the adverse weather in the Mersey estuary.”
The bridge has three pylons of different heights: an 80m high central tower, a 110m high tower on the north side and a 125m high south tower. The pylon heights were based on clearance required for aeroplanes using the nearby Liverpool John Lennon Airport, and on planning restrictions dictating where pylon foundations could be placed in the river. It has a trapezoidal post tensioned insitu reinforced concrete deck, with a maximum clearance of 23m above water level.
Building the bridge using marine vessels was not an option, due to the lack of water in the Mersey estuary. The construction team took an early decision to install a 1km long temporary trestle bridge across the river, from which all the concrete and reinforcement could be delivered, and to act as a platform for the main construction work on the structure.
Trestle access bridge
The trestle bridge was built simultaneously from each side of the river, using 12m long piles to support pre-assembled steel trestle deck sections topped with precast concrete planks. It meant that land-based plant could be used to dig the cofferdams for the main pylon foundations, as well as delivering all the concrete for the pylons.
The deck sections were built by balanced cantilever, with one 6m long section cast from both sides of each pylon every week – giving a total of 36m of deck construction per week. The deck sections are connected to the pylons by stay cables ranging in length from 41m to 226m.
The approach viaducts at each end of the main bridge are made up of multiple spans of 64m on the north side and 70m on the south. They also have cast concrete decks, and the JV again adopted formwork technology used elsewhere around the world in the form of a movable scaffold system (MSS). Two steel MSS units were built specially for the Mersey Gateway project, and had very complex geometry to cope with the curve and super-elevation of the approach viaducts.
Dochao says the construction team faced a range of different challenges: “On the north landside we faced the challenge of working on a brownfield site. As it is an old chemical industrial area, its ground was highly contaminated. By treating this material, we were able to reuse it in the embankments. As a result, we haven’t sent any material off site.”
Traffic management and communication
He adds: “In the south, the main challenges were traffic management and communicating with local businesses. The joint venture worked hard to ensure the local community has been kept updated, particularly through social media channels.”
Dochao says the team is very proud of its engagement with local communities. Although the project is welcomed by local residents and businesses, the construction work was always going to cause some disruption – especially the landside activities. Merseylink CCJV opened two visitor centres to inform people about the project, and to collect feedback that helped to improve or minimise the impact of the construction activities. These were staffed by volunteers from the local community.
Another success has been the establishment of the Mersey Gateway Environmental Trust, a charity set up to promote the conservation, protection and improvement of the environment across 1,600ha of the Upper Mersey Estuary from the new bridge up river to Warrington. “This team developed strategies that helped preserve important ecological sites, such as the salt marshes, as well as creating sustainable wildflower meadows at the Clifton roundabout in Runcorn,” explains Dochao. “The Trust will also manage a new 28.5ha nature reserve alongside the bridge, something that is unique for a major construction project in the UK. The Mersey Gateway really is a ‘green’ infrastructure project.”
“FCC is proud to work on such a major project in the UK. We want to use this knowledge of the market and this experience to win new opportunities in the future,” says Dochao.