Building bridges on a major dualling project in Wales

A465 Heads of the Valleys, Wales

Construction on the A465 Heads of the Valleys project has been ongoing since the early 2000s, with the final sections, section 5 and 6, due for completion in 2025. Work is being carried out to expand the route from Neath Port to Monmouthshire into a dual carriageway, which will improve traffic flow and make travelling from south-east to south-west Wales more accessible and safer. As the final sections of the project are underway, we wanted to reflect on our involvement across the project.

Sections 5 and 6

This phase comprised a mix of insitu and precast construction. Over thirty bridges are being built for the final section. Finishes across these structures range from a basic to fluted to a brick effect finish at the Jones Street site which was achieved using a reckli liner and TRIO formwork.

Abutments

For the abutments, our design team looked at how the formwork panels could be tied together without compromising the finish. The solution involved installing ties and walers from the back of the panels to minimise the visual impact on the concrete surface.

Along with the finish, the rate of rise and access requirements for pouring and installation were factors that determined the temporary works design for the tallest abutment which is 14 metres high. Larger formwork ties and additional walers were used to withstand a pressure of 80kN per sq m and achieve the 3-metre an hour pour rate.

Splayed Piers

Accessibility on bridge projects can often be challenging. Heads of the Valleys is no different, with many of the project’s piers and abutments situated in inaccessible areas.

The piers supporting the Nant-hir bridge are a prime example of this type of challenge, as the bridge crosses over the Nant Hir Reservoir. Adding to the complexity is the splayed shape of the piers which have been formed with TRIO to support the pour sequence and height.

As the piers were poured in two segments, using a panel system made it easier to extend the formwork without making changes to the fluting. Given the confined space on site, this would have been challenging to build with a traditional system as climbing platforms would be required to support the weight of the formwork.

Access across site

Multiple access requirements were fulfilled with PERI UP scaffolding. For the abutments, TVC required access from the ground up to facilitate the installation of steel reinforcement followed by formwork. The scaffolding was designed to serve both parts of this process with minimal adaptations required.

Typically, scaffolding towers at this height would be tied into permanent structures. In this case, lack of permanent structures meant the scaffolding had to be self-supporting with bracing and buttresses incorporated into the design for stability.

Access scaffolding has also been instrumental in prefabrication work. The PERI UP system was used to facilitate the build of reinforcement cages in a different location on site before they were repositioned in situ by crane.

Scaffolding has also facilitated the construction of the Taf Fawr bridge deck, with a 30m-high PERI UP 75 stair tower erected to provide an access point for Tecozam’s traveller system. A smaller staircase will connect the traveller to the main platform to support pouring operations.

Section 3

Between 2013 to 2015, improvements were made to a 7.8km stretch of the road between Brynmawr junction and Tredegar, also known as phase 3 of the Heads of the Valleys project. This phase involved upgrading the existing three-lane road to a dual carriageway, including a 3km surfaced cycleway.

We supplied our VARIOKIT parapet track and carriage to four bridges, which were made from a mix of steel and concrete. For access to the parapet track, we supplied our PERI UP scaffolding.