Managing piling obstruction risk intelligently for reinvention of a brutalist building

Northwood Investors are reinventing a 1980s Brutalist style London office building, “The Acre”, located in a densely populated urban environment, and surrounded by residential properties. There is a plethora of known and unknown obstructions beneath the site, including heavy steel grillages. Typically, such sites are redeveloped by total demolition and lengthy enabling works with significant vibration and noise. Instead, Northwood elected to selectively replace just 20% of the existing structure while upgrading and re-cladding the remaining 80% to create a modern development, with half the embodied carbon of the previously consented scheme. To make the scheme viable, Arup proposed the use of Pali Radice piles. This technique can construct mini-piles through layers of obstructions that would defeat traditional piling rigs, and can operate in constrained spaces such as existing basements. Despite the choice of piling technique limiting the pile diameter and tender options, this offered a step change in risk control and was crucial to enabling the project. Drilling trials and preliminary pile load testing were undertaken. The trials proved effectiveness of the technique and informed the pile design. Evidence from the trials permitted the method and programme to be assessed, and installation risks to be appropriately managed.