A323 Clay Shrinkage beneath flexible road

Project Background/Issue

Three sections of the A323 Aldershot Road were impacted by clay shrinkage and required a design solution by Geobear using geopolymer injections. The main issue addressed 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 affecting three areas of the road. A site investigation including four boreholes had been taken in the affected area and revealed London clay formation soil. 

With the information from the site investigations, Geobear designed an injection plan to reduce the shrinkable capacity of the clay and the road was subsequently resurfaced. 

Alternative options

The primary alternative considered was 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 and less viable due to the busy nature of the road.

Geobear Solution

Geobear proposed a solution using their clay shrinkage treatment. The team conducted injections at pre-designed locations in a grid horizontally and upto 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, geopolymer 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 carbon footprint study has indicated that the geobear solution releases 60% less carbon than traditional methods.

Timely Completion: The project was completed in mid-October, addressing the undulations and preventing further shrinkage of the clay.

Conclusion

The A323 Aldershot Road project demonstrates the success of Geobear’s innovative approach to road maintenance. By addressing the root cause of the undulations through clay shrinkage treatment, the company provided a cost-effective, environmentally friendly, and non-disruptive solution, showcasing the potential for similar applications in road infrastructure projects.