The sloping rooflight in the Provost’s Garden conceals a 650 sq m library extension
The challenge
The expansion of Queen’s College Oxford’s historic library involved the excavation and building of a 50m underground basement extension beneath the Provost’s Garden, while keeping part of the building open for students.
The context
The aim of the New Library is to house 150,000 modern and antiquarian books previously stored around the college and in the university’s Bodleian Library. The extension, which provides an extra 650 sq m of space, offers a high level of security in terms of both fire and theft protection.
Beard Construction was appointed as contractor for the £6.5m project, which began in June 2015. Excavation had to be completed without disturbing the college’s original Grade I-listed library building, which was built in the 1690s, as well as the 200-year-old wisteria and copper beech trees, and the Grade II-listed walls that surround the garden.
The old library is seen through the rooflight
The New Library houses 150,000 books
Logistics was a major challenge, says Paul Renton-Rose, Beard’s project manager. “Almost 9,000 tonnes of excavated spoil had to be brought out, and 3,000 tonnes of concrete and new materials transported through the tight restrictions of Queen’s Lane and New College Lane,” he explains.
Prior to installation of the basement’s secant piling, a reinforced piling mat, comprising approximately 1,000 tonnes of stone, was created to provide support for the piling rig.
To protect the west side of the existing library facade during construction, a 5.5m-high screen, made from steel supports, ply and Monoflex sheeting, was erected.
The solution
To overcome the tight space for excavation, Beard restricted the size and width of delivery vehicles and, in some cases, the materials delivered. Daily cleaning of the lane by site staff and weekly cleaning with a road sweeper was required.
Moling equipment was used to install services under the lawn, a saving on cost and disruption compared to trenching and landscaping.
Work had to be carried out without disturbing the 200-year-old wisteria and copper beech trees, and the Grade II-listed walls that surround the garden
The new basement was constructed using secant piled walls, which also provided protection for the Grade II-listed walls and an existing storage cellar. A temporary works system was installed to support the basement excavation until the permanent structure was completed.
The entrance to the New Library was created after the piling phase, and Beard had to use hand excavation to remove around 450 cu m of spoil so as not to damage the piles. “The groundworks team had to take great care not to cause too much disruption where the works interfaced with the live college,” says Renton-Rose.
The reinforced concrete walls of the basement were then fitted with insulation and damp-proofing for ideal storage conditions.
One of the signature features of the new library is a sloping rooflight, which gives views up to the west elevation of the old library.
The extension offers a high level of sercurity in terms of both fire and theft protection.
