Foundation Reuse and Strengthening Works at 65 and 67-69 Whitfield Street, LondonÂ-Paper

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The paper describes the reuse and strengthening of foundations beneath two central London buildings, 65 and 67–69 Whitfield Street, each extended by two storeys while retaining its existing structural frame. Because little was known about the foundations, the project used a risk-based approach combining staged investigations, structural and geotechnical assessment, and construction monitoring.<br /><br />At 65 Whitfield Street, investigations found 1950s bored piles that were short, variable in length and insufficient to justify the increased loads. Low-headroom mini piles were installed around existing pile caps to carry additional loads. Bespoke connections transferred loads from internal columns through reinforced collars around the existing caps, and from edge columns through transfer beams to new pile caps. The design accounted for how load would be shared between old and new piles.<br /><br />At 67–69 Whitfield Street, deep investigations revealed 1930s mass-concrete pad foundations about three metres below the floor, bearing on Terrace Gravels. Their dimensions, concrete condition and the underlying ground were assessed. Most foundations could be reused through load balancing; those with larger load increases received additional geotechnical and structural checks. The assessments indicated adequate capacity and generally small predicted settlements.<br /><br />The works relied on early, targeted investigations and ongoing coordination between structural and geotechnical teams, with risks and responsibilities agreed with the client and insurers. Remaining uncertainties—including possible weaker ground or concrete—were managed through monitoring of every column during construction. Measured movements at both buildings were less than 5 mm and within specified limits.<br /><br />The project demonstrates that foundation reuse can support sustainable redevelopment, but requires a clear risk strategy, sufficient investigation, and strengthening where load increases or uncertainty warrant it.

Keywords

foundation reuse

London buildings

structural strengthening

geotechnical assessment

bored piles

mass-concrete foundations

load transfer

mini piles

settlement monitoring

sustainable redevelopment