Britain’s biggest road-building project, delivered by Highways England, opened for traffic eight months ahead of schedule on Tuesday 5th May. The upgraded road was originally planned to open to traffic by December 2020, but now the last of the 24/7 roadworks have been removed and the new lanes are available for traffic, eight months ahead of schedule. Construction Worx Lite talks to Highways England about a particular challenge presented to the A14 Integrated Delivery team, the removal of the original A14 viaduct.
The £1.5bn A14 Cambridge to Huntingdon improvement scheme, which officially started in November 2016, is currently being delivered on behalf of Highways England by the A14 Integrated Delivery Team. It includes a major new bypass to the south of Huntingdon and upgrades to 21 miles of the A14.
With the new sections of the A14 now open and in use, works have begun to transform the old A14 for local journeys in and around Huntingdon, providing new link roads and demolishing the concrete viaduct that has been a landmark of the town since its construction in the 1970s. The viaduct has been hampered by defects requiring continuous and careful maintenance, including two separate strengthening projects in 2010 and 2013. As Highways England Project Manager Chris Bayliss explains, “The A14 viaduct has been a very prominent feature in Huntingdon for years but would have needed significant funds to repair and retain. Moving the new A14 away from the town has given us the opportunity to remove it, a decision that will not only improve the air quality and reduce noise in the town but will also aid regeneration and economic growth.”
Removal of this 16,400t prestressed concrete structure is one of the more complex tasks that the A14 team has tackled.
The viaduct forms the top section of a three-tier arrangement, sitting above a major road and the East Coast Mainline below. With traditional demolition approaches requiring substantial closures of these two key transport links, the team took a more novel approach allowing both road and railway to remain operational throughout the works. As Chris Law, A14 Integrated Delivery Team Engineering Manager explains, “Shutting either the road or railway for an extended period of time would have been enormously disruptive for the local community and wider businesses and commuters, so for this project traditional demolition was not going to be an option.”
Instead the central span of the viaduct which spans over the road and railway, will be lifted out from above, working from the existing bridge deck at all times. On Christmas Day 2019, the team from sub-contractor Pro Steel Engineering installed a bespoke, sliding, lightweight access deck to provide a working platform beneath the bridge. Its unusual stepped shape maintains headroom above the road for buses and HGVs whilst providing a sloped deck for water management and a higher working space where possible.
This central span of the bridge is made up of eighteen 32m longitudinal prestressed concrete beams each weighing between 90t and 185t. These beams will be carefully cut apart and lifted out one at a time over the spring and summer of 2020. Like all aspects of the removal works, no normal crane can be used for the task. Instead, the team have collaborated with Mammoet to deliver a bespoke 165t steel lifting gantry which spans the two sides of the bridge and can lift each beam out and slide it safely onto Self-Propelled-Mobile-Transport vehicles (SPMTs), before driving the beams offsite to be crushed and recycled.
So far, nine beams in the central span have been removed, with all beams due to be removed by August. Following that, works will begin to demolish the further five approach spans. A time lapse video of one of the beam lifts can be seen here.
Construction Worx Lite is keeping in regular contact with the Highways England integrated delivery team on the A14 project watch this space for progress reports on this exciting infrastructure project…