Balfour Beatty VINCI's HS2 Birmingham dive-under is in progress

Balfour Beatty VINCI has begun work on the Birmingham Spur Dive-Under at HS2's Delta Junction, with support from PERI UK. The project includes a 400-metre concrete structure with walls reaching up to 11 metres high.

The dive-under is north of Birmingham in one of the most complex sections of the high-speed rail scheme, where one railway line passes beneath another instead of crossing at the same level.

PERI supplied formwork, scaffolding and construction accessories for the project, including MAXIMO panel formwork for foundations, VARIO girder wall formwork for the main walls, PERI UP Flex modular scaffolding for access and shoring, BECOSTOP permanent end-stops for slab joints, and SCS equipment for roof slab construction.

The main engineering challenge was the height of the walls, which increased pressure on the formwork during concrete pours. BBV used PERI's VARIO system for the wall sections because its girders, walers and ties could be set closer together than on fixed-frame panel systems.

"Because we designed this in component form, we put the girders, walers and ties closer together to cope with the higher concrete pressures," said Dan Biggs, Senior Sales Engineer, PERI UK.

"With a standard panel, the frame layout and therefore capacity is fixed; you can't change it to make it stronger. The higher the wall, the greater the pressure, so the VARIO system was essential to handle the loads generated by an 11 m high pour."

Coordinated supply

The project also relied on coordinated design between the formwork and access systems. PERI's internal engineering teams aligned the layout of the wall formwork and access scaffold before materials reached site, helping to avoid clashes during installation.

The arrangement reduced the number of separate suppliers involved and supported access for rebar fixing on the tall wall sections.

Mustafa Ozhan, Section Manager, Balfour Beatty VINCI JV, described the approach in operational terms. "The formwork and scaffolding systems PERI UK proposed enabled us to complete our construction works efficiently and without issues. At the same time, the site support team demonstrated the capability to listen to our needs and develop tailored solutions accordingly."

Further along the structure, the team used the BECOSTOP permanent stop-end system in heavily reinforced slab areas, where timber-based methods would have been more difficult and time-consuming. The steel mesh system remained in place after the pour.

For the roof slab edge, SCS brackets were fixed directly to the completed walls to create a high-level working platform. This gave access for reinforcement work and later supported MAXIMO panel formwork and fresh concrete loads during the slab edge pour, removing the need for through-ties in the structure and avoiding ground-based support.

Pressure data

Concrete pressure sensors were used on selected wall pours to monitor site conditions in real time. The devices allowed the project team to compare actual pressure levels with design assumptions during construction of the taller sections.

"The sensors provided an additional layer of assurance for the project team," said Biggs.

"By monitoring pressures in real time, we were able to compare live site data with our design calculations and demonstrate how the formwork was performing during the pours. It's another example of how PERI can support customers with both engineering expertise and digital technologies, rather than simply supplying equipment."

The data formed part of the engineering support for the pours and was used to validate the formwork's behaviour under site conditions.

Working relationship

The wider package reflects an established relationship between the two companies on major civil engineering work. PERI assigned engineers and a project manager to the job as part of the delivery structure.

Biggs linked the scale of the package to both logistics and design support. "I think it's a combination of factors.

"It's PERI UK's capability to deliver big projects, whether that's from a service point of view, the ability to deal with large volumes, the range of systems we've got, or the quality and familiarity of the equipment. We also appointed a full team of engineers and a project manager to ensure the delivery goes smoothly. It's all about providing a complete solution."

Nicolas Ferard of Balfour Beatty VINCI JV said the use of a dedicated team improved accountability on the structure. "Based on my experience working on other projects, having multiple designers led to reduced ownership and engagement. For this structure, the collaborative approach and the assignment of a dedicated team created a more positive outcome."