Challenge
Settlement beneath the A47 Bretton subway approach slabs caused uneven surfacing and ride quality issues; a rapid stabilisation was required without prolonged carriageway closures on this key urban route.
Solution
Geobear delivered targeted geopolymer injection beneath the affected carriageway to fill voids, improve subgrade strength and re‑level slabs during restricted working windows with minimal disruption.
Measured slab settlement prior to treatment
Programme delivered in traffic management windows
Rapid return to service after injection
The A47 Bretton subway in Peterborough forms part of a strategic urban corridor carrying significant daily traffic. Settlement had developed beneath sections of the carriageway approaching the subway structure, resulting in uneven running surfaces and a noticeable deterioration in ride quality.
Investigations identified voiding and sub‑base degradation beneath the concrete slabs, likely associated with water ingress and long‑term trafficking. Without intervention, continued movement risked further deterioration and increased maintenance liability.
The location sits on a heavily trafficked section of the A47 where extended closures would have caused significant disruption. Traditional excavation and slab replacement would require substantial traffic management, longer construction duration and higher embodied carbon.
A solution was required that addressed the underlying loss of support, restored levels accurately and could be delivered within restricted working windows while maintaining daytime traffic flow.
Geobear designed a targeted geopolymer injection programme to stabilise and re‑support the affected slabs. Small‑diameter injection points were drilled through the carriageway at predetermined centres. The two‑part geopolymer was injected beneath the slabs where it expanded to fill voids, re‑compact loosened sub‑base material and improve bearing capacity. Controlled expansion enabled precise re‑levelling of the settled slabs, monitored in real time to ensure movement remained within specification.
Works were undertaken within planned traffic management windows. The rapid curing characteristics of the geopolymer meant treated areas were trafficable shortly after completion, allowing the route to reopen promptly.
The intervention reinstated slab support and corrected differential settlement without the need for excavation or slab replacement. Ride quality improved and the underlying voiding mechanism was addressed. The works were delivered within the agreed programme and without prolonged carriageway closure, reducing disruption to road users while providing a technically robust stabilisation outcome.
Get in touch with our expert team today and discover how Geobear can extend the life of your critical infrastructure assets.
