Project Background/Issue
Surrey Country Council was facing a significant challenge affecting a section of one of its roads, the A323. Surface undulation due to issues below ground had caused the asphalt to crack affecting traffic on the route. The road quality was gradually worsening and Surrey CC needed to find a solution that would not impact road users or the local community including a school.
Three sections of the A323 (Aldershot Road) were impacted by clay shrinkage. The main issue was the undulating condition of the road, resulting in poor ride quality for drivers. The undulations worsened, particularly after a hot summer towards the end of 2022.
The road was a standard flexible construction, however, the soil beneath was shrinkable clay, and the adjacent trees with roots exacerbated the shrink-swell phenomenon. A site investigation including four boreholes had been taken in the affected area and revealed London clay formation soil.
Having researched potential options, Geobear was consulted due to its expertise in delivering minimally intrusive infrastructure projects and particularly its expertise in working with clay soil. In this case, the requirement was to use its clay stabilisation solution to minimise the shrink-swell potential of the deep-lying clay ahead of road resurfacing
Alternative options
The primary alternative considered was mass excavation and replacement, but the challenge lay in the extensive influence of tree roots at depth, making it an impractical and costly option. Complete excavation would have been disruptive, potentially taking months and less viable due to the busy nature of the road. Closing the road for a significant amount of time would have impacted the local school and businesses making it unviable for Surrey CC.
Geobear Solution
Geobear proposed a clay shrinkage solution that could be delivered during overnight shifts, requiring single-lane closures. Geobear’s solutions provide long-term asset life extension and are delivered ultra-fast compared to alternative methods, this means there was little to no impact on the local school or community. Furthermore, the Geobear approach is kinder to the environment, with carbon emissions 70% lower than alternatives.
The engineered design solution was also delivered by Geobear’s technical experts onsite. The team conducted injections at pre-designed locations in a grid horizontally and up to 3.1 meters below the surface, covering specific sections of the road. The first step in the process is to mark the injection locations on the road surface, the locations are then drilled and injection tubes are inserted. Once in place, a specialist geopolymer material is injected into the holes at pre-determined depths. The tubes are then removed and the small holes are filled with grout.
This method addressed the clay shrinkage issue without the need for excavation. The treatment occurred overnight to minimise disruptions to the busy road.
Benefits
Non-disruptive Solution: Geobear’s approach allowed the road to remain open after each shift, minimising disruption to traffic.
Cost-Effectiveness: While the cost was comparable to excavation, the benefits included less disruption and the ability to open the road after each treatment, providing cost savings in terms of traffic management and associated logistical considerations.
Environmental Impact: The treatment preserved the trees along the road, eliminating the need for their removal. This not only contributed to environmental conservation but also aligned with carbon sequestration efforts, offering additional benefits beyond the immediate project. Furthermore, a review has indicated that the Geobear solution releases 70% less carbon than traditional methods would on this scheme.
Timely Completion: The project was completed in mid-October, addressing the undulations and preventing further shrinkage of the clay – it was completed in 10 days as opposed to months with an alternative.
Carbon Savings
The A323 Aldershot Road Project serves as a model for environmentally conscious road maintenance projects. The choice of geopolymer as a material for ground improvement played a pivotal role in reducing the carbon footprint.
Traditional excavation and replacement methods would have emitted 138 tonnes of CO2e, while the geopolymer alternative emitted only 42 tonnes.
Based on a direct comparison to what would have been a tried and tested traditional method of delivery of excavate and replace, Geobear delivered a 70% reduction in carbon emissions which highlights the project’s dedication to sustainable practices.
This is equivalent to saving 31 trees with a 500mm trunk diameter (3.1 tonnes/tree over 20 yrs).
Conclusion
The A323 presented significant challenges due to the location and nature of the issue. Full closure of the road would have impacted nearby amenities such as a school and local pub, therefore a non-disruptive, low-impact solution was sought. Surrey County Council thoroughly researched options and considered the solutions delivered by Geobear to be the most effective. Geobear delivered a low-carbon, long-term solution that could be delivered with minimal impact on the local community.
Following the Geobear clay stabilisation solution, the road was resurfaced to address the existing undulations, resulting in a stable asset for the long term.
Client Testimonial
“Our priority is delivering cost-effective solutions for the travelling public in Surrey, which cause as little disruption as possible which the Geobear solution provides,”
“We approached Geobear because it ticked many boxes for us: its solution is swift, economical, low carbon, enhances workplace safety and preserves access to surrounding utilities.”
Amanda Richards, Assistant Director of Highways at Surrey County Council and chair of the UK Roads Boards’ Road Condition Management Group
Awards
The project’s success has been recognised by the Chartered Institution of Highways and Transportation, achieving highly commended status and the scheme also won the Project of the Year category at the Ground Engineering Awards.
