Background
Many cracks in walls around school
A school in South West London had experienced differential settlement of the foundations of the building perimeter. The first signs of a problem were the cracks that began to appear throughout the school on the walls. The foundations of the building were sinking foundations on all corners.
The cause of the settlement was clay shrinkage. This phenomenon causes seasonal movement of buildings due to the shrink-swell of high plasticity clay soils. As the soil dries and hydrates it acts like a sponge causing the foundations of the building above to move. In very dry summers this movement is exacerbated and can cause significant damage.
Geobear was contracted to provide a solution that would stabilise the soils and prevent future movement from occurring.
Customer alternatives
Clay Shrinkage is a common problem across the swathes of clayey soils in London and other parts of the UK. In order to prevent shrink-swell occurring and to stabilise the school the options were limited.
Lifted floor and tubes for injections
Options included piling the existing foundations to depths of 15 metres, however, this was a high-cost alternative and the school would need to be closed for up to one year. Some underpinning had been trialled in some areas but had not succeeded. The extreme solution would have been the demolition of the building which would require a complete rebuild – this was not a viable option for the school.
Geobear Solution
The Geobear solution utilises geopolymer injection, which involves the drilling and insertion of tubes beneath the foundation to inject an expensive geopolymer material at multiple depths. Once the material is injected it expands and hardens, compression the existing soils and creating a stable base for the buildings’ foundations.
Geobear has up to 30 different materials and used a specialist variant that was suited to the site conditions. The treatment extended to 120 linear metres of the perimeter foundations and load-bearing walls and the material was injected to depths up 4.5meter below ground level.
One critical benefit to the Geobear solution was that it could be delivered within the window of the school summer holidays. As a fee-paying school, this reduced any need for closure and the pupils and the community would not be impacted.
Lack of disruption to the school
Geobear was responsible for all the site works. We were the principal designer and principal contractor for the scheme and we undertook all the enabling works, including drainage repairs and locating services to ensure the site was safe to work. We also handed back the site in the same condition as it was received – clean with no obvious signs that the work had taken place.
The project was delivered by Geobear’s in-house project management and technical teams, ensuring any site issues could be swiftly dealt with. This enabled the hand back to happen without delay so the school opened after the summer holidays as planned.
Now the school building has been stabilised, the client now has the confidence to invest in further improvement of the asset.
