The second phase of a massive project to remodel the Catthorpe Interchange - a bottleneck on the motorway and trunk road network - is now underway.
After a two year absence, cones and temporary barriers are once more in evidence at the Catthorpe Interchange in Leicestershire, and will be until the end of 2016 as the junction undergoes a major rebuild. This is the point on the Highways Agency’s network where the A14 meets the M1 and the start of the M6. Skanska built a new M6 to M1 southbound viaduct and then demolished its life-expired predecessor at Catthorpe between 2010 and 2012, and now the contractor is back on site for the full remodelling.
Skanska and design partner Jacobs were first appointed as the early contractor involvement (ECI) team for the interchange in 2005. Since then, the Catthorpe scheme has been through almost a decade of political machinations and come out the other side looking considerably different to the project first proposed (see box p16).
Since setting up on site in autumn 2013, Skanska has achieved a lot, despite high rainfall in February and frosts in March this year, which delayed the ecological work of transferring newts to a new habitat.
The contractor is tackling a typically complex junction reconstruction job. Essentially, the task is one of sequentially diverting traffic onto temporary or new permanent carriageway to free up areas to work on.
At the end of June, Skanska was due to reach the fourth of 22 main traffic management phases, switching the M1 into contraflow on the northbound carriageway. With this contraflow in place, piling can start for a massive new M1 underbridge, which will be built top down in two halves.
The remodelling will fundamentally change the way the A14, M1 and M6 interchange at Catthorpe by creating free-flow links between the A14 and the two motorways. At present, the connection is made by a dumb-bell layout at low level, which also joins with a number of local roads and will be returned to local use only as soon as traffic can be switched onto the new direct links.
The A14-M1 connections will be at high level - the northbound on a 280m steel viaduct, the southbound on embankment. A new dual carriageway M6-A14 link will be dug out below - part of a 500,000m3 earthworks programme - and built through the new M1 underbridge.
So far, a great deal of ecological and preliminary works have been done, piling is under way for the abutments and piers of the major structures, and the first two main traffic switches have been put into effect.
The first of these switches moved M1 northbound traffic over to create room for work to build a pier of the A14 to M1 northbound viaduct in the central reservation of the M1. The second diverted M6 southbound traffic within an area to the west coined the “golden triangle” because so much work is concentrated there.
“What’s been done at this specific location gives a good example of the benefits of ECI,” says Highways Agency project manager Ivan Marriott. “We have a new viaduct to build to take the existing M6-M1 southbound link over the new M6-A14 dual carriageway. Construction of the southerly abutment of this viaduct tight up against live traffic would have been difficult, very complex, but construction of temporary lanes linking the north andsouthbound M6-M1 links has opened up the area and means the abutment can be built in a more straightforward, conventional fashion.”
“While we may be a matter of a few days behind programme, we are hitting our major milestones more or less on time”
Ivan Marriott, Highways Agency
The three main structures of the Catthorpe project - the M6-M1 viaduct, the M1 underbridge and the A14 to M1 northbound viaduct - will all be built with weathering steel beams, for whole life cost and maintenance purposes, on piled reinforced concrete piers and abutments.
Every element of the project is being managed via a building information modelling (BIM) model that includes the full construction programme modelled in sequence as-planned and as-built. “This has been very useful for showing the impact of changes made as a consequence of poor weather earlier in the year,” says Skanska BIM manager Robert Hicks.
“We have large volumes of material to cut out, and could see we were going to be up against it on time, so it made sense to switch tactics and use the time to do other work.
“The sequencing of piling was changed. Using the BIM model we could see the knock-on effects later in the programme.”
Work brought forward included piling for the wing walls of the M1 underbridge, as the wall foundations are outside the influence of the M1, says Marriott.
Temporary sheet piling is in place in the central reserve ready for the traffic switch, initial excavation and abutment piling of the M1 underbridge.
“We’ve now got a lot of large scale civil engineering work going on, and while we may be a matter of a few days behind programme, we are hitting our major milestones more or less on time,” Marriott says. “Both halves of the M1 underbridge are due to be finished by June 2015, which will give us access to do a lot more work in the western area.
“We have target dates of March 2016 for having the new A14/M6 link available and June 2016 for having it open in both directions,” he continues.
“That year all of the main links will open, congestion will start to ease and we can then get in and finish all of the local roadworks.”
HIstory in the making
Plans to upgrade Catthorpe Interchange date back to the 1998 New Deal for Trunk Roads white paper. The initial designs that followed were for a four level “all movement” junction that included a massive M6-M1 southbound viaduct at the highest level.
But by 2008, then roads minister Stephen Ladyman had asked the Highways Agency to review the plans, “to go back to basics on what the scheme was trying to achieve”, according to the Agency’s project manager Ivan Marriott.
A consultation was held on three options, with or without different levels of improvement to local roads, which led to the adoption of the outline of what is now being built. The project has been scaled back, with links from the M6 to M1 north and between the A14 and M1 south removed.
Marriott defends this as sensible in the context of the wider road network. “Traffic modelling doesn’t support these links because there are other good ways of making these journey paths elsewhere,” he says.
The scheme that was selected - and successfully went through public inquiry with draft orders and environmental statement in place - still had to endure being put on hold in 2010. Skanska was awarded a contract through the Agency’s capital maintenance programme to replace the life-expired M6-M1 viaduct. Then, a year later, government ordered the junction rebuild back on again as it was deemed to be a key growth stimulus - 20% of M6-A14 traffic through the heavily congested Catthorpe Interchange is freight.
The whole process of traffic modelling, environmental statement and statutory procedures had to start again towards a new public inquiry, with further cost savings sought.
“Teams across all Agency projects were asked to produce 20% cost reductions,” says Marriott. “Value engineering with Skanska showed we could marginally scale back the length of some slip roads and generally reduce the footprint of the scheme, so avoid replacing or widening overbridges on the M1 and M6 approaches.”
The £229M out-turn project budget of 2010 was reduced to £190M, although the target cost of Skanska’s NEC Option C contract is £128.5M. “Through all of this time, consultations have consistently been in favour of doing this improvement, which has been all about balancing costs, environmental impact and realistic need,” says Marriott.
“Locally, the scheme will remove communities’ direct link to the junction, which is a compromise. But they will get a dedicated connection to the trunk road network via the nearby A5, plus a better local network of roads and cycleways and re-established rights of way, including bridleways.”