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Settle down

Piling and foundations

A bungalow near Peterborough that had subsided because of clay shrinkage has been relevelled with injections of geopolymer resins into the sub-base.

The building suffered from almost immediate subsidence when it was constructed in the mid-1990s. Large trees surrounding the property were removed to avoid further moisture being removed from the ground and settlement was monitored until 2004, when it was determined that movement had stopped.

By that time, one half of the bungalow had settled relative to the other by about 90mm, causing cracking to appear in the interior. Piling was considered, but would have been difficult as the property was built on three separate rafts.

'The owner was ready to demolish the property and rebuild, as the only cost-effective option, ' explains contractor Uretek's operations manager Simon Scott.

'However, we had successfully treated the smallest of the three rafts four years ago, so he was willing to try resin injection for the main structure, ' he adds.

The Uretek team was on site for two weeks, using a combination of mechanical jacking and injecting specialised expansive resin into the sub-base.

The resin quickly consolidated the sub-base and expanded in an upwards direction to gently lift the raft. Movement was carefully monitored by laser levels.

After a fortnight the building was lifted back to the required datum. 'There was a small amount of residual settlement, which we were able to correct, ' says Scott.

'It was a success story.

The brickwork that had been displaced by the original movement was pushed back into position so little superstructure repair was required.'

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