Strip footings for the extension of a piled building

A four-storey building in south-west London, UK is to be extended to eight storeys by introducing a system of strip footings to supplement the original foundation system, formed by displacement flight auger piles. The reuse of the original foundation piles and the implementation of the new footings were made possible by a detailed desk study, which obtained record information on the existing foundation system together with a thorough investigation of the existing foundations, which validated the record data. The strip footing solution was assessed against other options and selected on the basis of accessibility and construction practicalities. New ground beams were designed to distribute the new column loads in a manner compatible with the implemented solution. The complex interaction between the new shallow footings and the existing deep footings was assessed considering different loading scenarios and maximum and minimum displacements for each element. Simplified linear elastic geotechnical analyses and pile settlement calculations supported the structural assessment of the proposed extension.