Solutions to both tree root and backfill subsidence
Client: Local authority technical services department
All parties to the contract agreed that the contract had a successful outcome and was achieved with the minimum of disruption.
Pelham Road, London N22
There were two causes of the subsidence affecting this property which was built on differing ground conditions. The rear of the building was on London clay and was suffering subsidence caused by the roots of an oak tree in the back garden.
In contrast, the front of the house had been slowly subsiding over many years as it was built on backfill placed on the site in Victorian times after the River Moselle was culverted immediately adjacent to the property.
The local authority designed a traditional underpinning scheme using transition beams at each end of the main body of underpinning. The depth of the underpinning was varied to take account of different ground conditions.
Excavation at the rear of the building was down to 3.5 metres where there was moist clay unaffected by tree root action and therefore suitable to found the underpinning.
At the front, the excavation was even deeper at 4.5 metres through made ground. At this point a firm bearing stratum was found which was suitable for the underpinning. We needed to take great care throughout the excavation through the made ground and an intricate closeboarded timber shoring system was designed to protect both the works and our team.
The flank walls were an added complication. They were on the public highway and required street works licences to open up and then reinstate the surfaces to the council's approved standard. Safe working systems were implemented to make sure that the public were not in any danger from our works.
All parties to the contract agreed that the contract had a successful outcome and was achieved with the minimum of disruption.
