SPECIALLY MADE precast concrete culvert units allowed construction of water storage facilities beneath the courtyard of London's Royal Academy of Arts to be carried out with minimal disruption to visitors.
The Royal Academy is in Burlington House on Piccadilly.
Over the past two years, builder Poultney Gallagher has been carrying out a major refurbishment of the courtyard. Public access had to be maintained during opening hours, seven days a week.
In the scheme by architect Michael Hopkins and Partners, new fountains meant the pumps and 30,000 litres of water had to be stored underground.
Poultney Gallagher suggested building the room from precast sections. Engineer Harris and Sutherland developed the idea to include tank rooms, plant rooms and storage. A corridor links the new space with the RA vaults.
The units were manufactured by Milton Pipes. Each was designed to take the load from a 300t crane used in the courtyard.
Two end sections, each weighing 17t, were specially cast. Fourteen 3m wide, 2.75m high and 1m long box culverts, weighing 8.5t, and eleven 8t C-shaped units were cast in the firm's moulds with one wall eliminated.
Installation was difficult in the restricted space. Placement was to tight tolerances, +/- 6mm vertically and 150mm horizontally, dictated by the level of the vaults, ramped entrance paving and the electrical feed from a substation.
For accurate placement, steel T-sections were cast in the base slab. These were levelled so the units met the vertical tolerance and greased to allow them to be jacked together accurately.
The 28m long, 10m wide and 4.5m deep excavation was carried out in two parts to minimise disruption. Units were delivered in batches of four or five and craned into position before 6am. They were then positioned and topped with a reinforced concrete slab and the paving.