Background
A section of a busy dual carriageway, near a town in the south of England experienced ground instability, leading to subsidence and voids beneath the carriageway. The client required a comprehensive ground improvement plan to address these issues that were identified using Ground Penetrating Radar (GPR) and Dynamic Cone Penetration (DCP) tests. A solution was needed to improve the existing ground and address the voids discovered before future resurfacing.
Alternative Solutions
The location of the road, adjacent to a commuter town, was heavily used, meaning any intervention to improve the ground at the site needed to be conducted with minimal impact on traffic. Traditional approaches, such as excavation and backfilling, were not feasible, as the southbound carriageway would require a full closure for many weeks.
The local county council required a solution that could be implemented without impacting road users and selected a geopolymer solution designed by Geobear.
Why Geobear?
The Geobear design solution utilises geopolymer injection and requires no excavation. It is fast to implement, and roads can be reopened within an hour after injecting the geopolymer material. Mobile injection units, housing all the equipment and materials, can be driven onto the site, and the design solution can be implemented quickly on sections of road.
In this instance, the southbound carriageway was closed overnight while Geobear delivered the works as subsidiary contracting work was also taking place. However, Geobear can work in isolated lane closures on sites where access is still required, further minimising disruption.
Carbon Saving
The Geobear solution is a low-carbon alternative to traditional excavation. Carbon Footprint Ltd calculated that in a scenario comparing full concrete slab replacement to life extension by Geobear, there were 62% lower carbon emissions using the Geobear method. Broadly speaking, in most scenarios in the highways sector, Geobear would deliver a similar carbon saving. Read the report here.
Road Traffic Delays
Transport consultants Volterra compiled a report calculating the indirect costs associated with traffic delays and how using a Geobear design would provide indirect savings to the communities. By modelling Geobear’s typical performance improvements on road projects against major and minor highway projects, Volterra was able to estimate the cost impact of faster maintenance, which totalled £87 million per year in the UK. See the website for more.
Geobear Solution
The core objective was to design a geopolymer injection solution to improve the ground and prevent movement of the pavement structure by reinstating the contact between the carriageway underside and the underlying soils. Geopolymer is injected as a liquid that mixes and reacts in the ground to create an expanding geopolymer material that fills voids and solidifies. The geopolymer is injected under pressure, migrating into microvoids and fissures in the ground, where it expands and solidifies to strengthen subbase/subgrade layers.
The implementation of the Geobear design resulted in ground consolidation, which addressed features identified in the GPR survey, including voids, ground disturbances, and subsidence.
On-site Delivery Process
Working with the client, Geobear delivered the geopolymer injection works within the allocated timescale. The process included:
- Service Scanning: A preliminary scan for buried services, marking them on-site.
- Traffic Management: Full closure, lights, and other traffic management measures were implemented each night shift, with the road opening during the day for the public.
- Equipment Mobilisation: Geobear’s mobile injection units, equipped with the necessary materials, drilling, and injection tools, were positioned within the designated traffic management area. The injection units relocated once a section was treated.
- Drilling: Following a pre-designed pattern, a series of 14mm diameter holes were drilled through the pavement structure using handheld and rig-mounted combi drills.
- Injection Tubes: 12mm diameter tubes were manually inserted into the drilled holes.
- Geopolymer Injection: The geopolymer was injected via hoses, expanding up to 10-15 times its liquid volume to fill voids and compact underlying soils.
- Monitoring: Digital monitors and laser sensors were used to precisely control and monitor the ground consolidation process.
- Tube Removal: Injection tubes were removed manually or mechanically.
- Hole Sealing: Injection holes were filled with epoxy resin to restore surface integrity.
Project Outcomes
The project was completed three shifts ahead of schedule (delivered in 12 shifts and planned for 15 shifts), minimising disruption to road users.
The use of geopolymer injection effectively addressed subsidence and voids, improving the overall stability and integrity of the carriageway. The collaboration between Geobear and the client, supported by detailed planning and rigorous safety protocols, ensured the project met its objectives on time and within budget.
