Burton Green Tunnel South Portal - ABM Precast Solutions Ltd
As part of the high-speed 2 rail infrastructure, the Burton Green Tunnel South Portal required a specialist engineering response to a unique challenge: the dispersal of air pressure caused by high-speed trains entering and exiting tunnels. The solution to this was designed by BBV and delivered in collaboration with ABM Precast Solutions Ltd, involved the construction of a fixed-height porous portal structure with pressure relief vents of varying size.
The scope included the delivery of 178 precast concrete roof units, each integral to managing aerodynamic pressure while forming part of a visually cohesive and structurally robust portal. What made this especially complex was the high level of variation, 96 unique dimensional combinations across the panel units, many of which featured vent chimneys of varying sizes.
To meet these challenges, ABM devised a flexible mechanical formwork solution, allowing a set of standard moulds to be rapidly adjusted and reconfigured throughout the production cycle. This enabled high-speed, high-accuracy manufacture without compromising on tolerances, a critical requirement given the structural demands of the portal units, which each weighed between 17 and 28 tonnes.
The inclusion of chimneys added another layer of complexity. While casting the units monolithically could have been an option, the presence of rebar projecting from the upper surface would have necessitated costly couplers and created issues in demoulding and turnover. Instead, ABM implemented a two-stage casting method. The main panels were cast first, with the chimneys added later using custom internal and external formwork. This approach ensured consistency, control and efficiency.
ABM also challenged the conventional method for creating construction joints at the interface between precast roof units and in-situ portal walls. Rather than rely on post-casting surface preparation, which adds time and labour, ABM proposed a cast, indented joint detail that complied with BS EN 1992-1-1, Clause 6.2.5. This alternative detail was accepted, eliminating the need for secondary preparation and streamlining the production process further.
Through technical innovation and a commitment to manufacturing efficiency, ABM successfully delivered all 178 portal units to exacting standards. The project demonstrates how complex pre-designed elements can be manufactured at scale and on time, when smart production engineering is applied to structural challenges.