Subsidence solution

When a primary school experienced subsidence, Finnish geotechnical engineers Geobear stabilised the structure with an innovative answer.

Old Fletton Primary School in Peterborough has welcomed pupils back following essential ground improvement works. The building, which houses two offices and three classrooms serving 438 children, had been rendered unusable due to subsidence and was in urgent need of repair.

Long-term settlement had caused cracks up to 20mm wide. Temporary acrow props had been in place for some time to support the structure and prevent further destabilisation while administrators sought a permanent resolution. But time was of the essence.

Headteacher Sarah Levy says: “Without this solution, the school would have needed temporary cabins to replace offices and classrooms, which would have been costly and disruptive to education.”

Peterborough City Council explored the options for restoring building safety and functionality over the summer holiday. It engaged Pick Everard to investigate the cause.

An assessment survey revealed that the settlement was caused by clay soil shrinkage combined with the proximity of tree roots, which had undermined the shallow 1.3-metre foundations.

With the building already underpinned, an alternative approach was required. Main contractor Lindum worked with Geobear as subcontractor because of its experience in soil stabilisation, void-filling, floor and slab relevelling, slab stabilisation and other ground improvement solutions in order to develop a plan to protect the school long-term.

Groundworks solution

Geobear created a perimeter ‘wall’ of geopolymer resin using 206 injection points around the entire perimeter of the building, with each injection point receiving 4kg of resin.

The material flows as a liquid into any voids or weak zones in the soil, then expands with immense pressure to compact the ground and strengthen it from underneath. This geopolymer solution cures to 90% of its full strength within minutes, providing immediate support through the holes.

The whole process was completed in 15 shifts to stabilise both the soil and the building, offering a quick yet long-term resolution for the school with minimal inconvenience or upheaval compared to traditional technologies such as underpinning.

“This is the fifth school Geobear has helped secure this year,” says Halil Kaygisiz, Area Manager for Commercial and Infrastructure at Geobear UK. “The goal is always to deliver a solution that provides pupils, parents and staff with peace of mind for the future.”

For more, visit geobear.com