We recently completed a close proximity secant wall at White Lion Street in London for Blenheim House Construction Ltd. The client was keen to maximise the basement footprint so we were tasked with installing secant pile as close to existing boundaries as possible.
In all 150m of secant wall was constructed to allow excavations of up to 6.5m. Piles were installed within 0.1m of occupied neighbouring properties. A Cased CFA solution was chosen to provide a highly accurate hard/hard secant wall configuration and to minimise disturbance to the surrounding soils during piling.
Due to the strict movement tolerances a propping system was designed to act above the capping beam so that the ground floor slab could be cast before props are removed. To facilitate load transfer from piles to props we installed steel sections into the hard primary (female) secant piles at prop locations. Cast-in steel was chosen over concrete nibs to allow easier removal once complete. Here are some photos from the installation works.