The second in a series of three reports from events exploring underground construction, held by Architecture Today in partnership with waterproofing specialist RIW

 
Subterranean City 1: Waterproofing Complex Basements
Alex Massingham, UK Technical Lead at RIW, explains the bespoke nature of waterproofing basement structures
Subterranean City 2: Expanding Institutions
In recent projects the British Museum, the V&A and UCL have dug deep to make the most of their campuses
Subterranean City 3: Dealing with Neighbours
Encountering restrictions both below and above ground at the Francis Crick Institute and the House in a Garden

Buildings.

In recent projects the British Museum, the Victoria & Albert Museum and University College London have dug deep to make the most of their campuses

John McElgunn, Partner at Rogers Stirk Harbour and Partners, on the World Conservation and Exhibitions Centre at the British Museum, completed in 2014

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The new building’s only street frontage, on Montague Place (ph: Paul Raftery)

“The site for the new building was a slightly tortured T-shape in the north-west corner of the British Museum campus, surrounded on seven sides by Grade-1-listed buildings, in a conservation area. At the northern end of site was the only street frontage – Montague Place – where there was a 1970s reproduction of a Georgian villa. The site included old services, bins for recycling, bits of plant and a road running through the middle which had to stay, as did all of the fire escapes and the windows that brought light and fresh air to seven departments. Permission was obtained from English Heritage to demolish a Victorian book-bindery on the site.”

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The site prior to demolition of the Victorian book-bindery

“Most of the movement of artefacts within the museum is done by hand. Special exhibitions space and storage was supported on cast iron scaffolding above the Reading Room, where it couldn’t take any loading and was very difficult to get things in and out, and the science and conservation areas were in old butler’s kitchens in the basements of Bedford Square.”

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There are three basement levels of storage, including the lowest level, B3, where Greek and Roman stone is kept, each roller rack carrying approximately 17 tonnes

“Ultimately we suggested that all the storage would have to go into the ground. We considered doing top-down construction, completing phase 1 – the interesting stuff – then continuing to dig down to create the storage space, but given the very sensitive scientific equipment that would already be in the new building, and the precious objects, we rejected that idea because of the vibrations. In order to maintain light levels, the building was made quite separate, just keying into the main building at the Great Court.”

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The glass-roofed atrium creates a light-filled science and research centre containing offices, meeting rooms and library facilities (ph: Paul Raftery)

“The science and conservation pavilion ended up going below ground. Because of the amount of equipment used – scanning electron microscopes, spectrometers and X-ray suites –  it is actually better there, although largely our goal was to get people above ground and into daylight. Approximately 50 per cent of the building is above and 50 per cent below ground.”

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Enough soil to fill 15 Olympic-sized swimming pools was excavated and white temporary props held back the surrounding earth

“We worked to a category zero tolerance – allowing us plus or minus 1mm movement in the existing buildings. All of the props had electronic strain gauges on them that were constantly monitored so that if a prop was taking more load than it should we knew that something was happening, that something was moving. We were going 25 metres below the foundations of the Duveen gallery containing the Elgin Marbles, we were next to the Coptic corridor and the Percival David Foundation collection of Japanese ceramics, and none of these artefacts were moved during construction.”

A lorry accessing the 42-tonne vehicle lift from Montague Place; the lift is completely hidden from view
when not in use (ph: Paul Raftery)

“Understanding what would happen to water below ground, and how to build on this scale was quite daunting. At our peak we were removing 100 truckloads of soil a day. Between the secant pile and the inside of this building we had five levels of moisture protection; the capacity for any moisture to enter the building was completely unacceptable.

The secant was specified to be dry, so any gaps where moisture initially came through were grouted(1), then the RIW 20 system connected to a sealed cavity drain. Joints were plugged and taped to prevent water and water vapour (2). Then a 100mm cavity which contained an electronic leak detections system (3). Then a 100mm dense blockwork wall (4) with external grade paint on the inside face (5)

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Extensive below-ground storage space (ph: Paul Raftery)

“Given the preciousness and fragility of the its contents the capacity for any moisture to enter the building was completely unacceptable.”

Alice Dietsch, Director at AL_A and Alice Blair, Associate Structural Engineer at Arup, on the V&A Exhibition Road Quarter project, completed in 2017

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ph: Hufton & Crow

“The brief was to build a new major exhibition space below ground. The site at the V&A was occupied by back-of-house buildings and facilities for schools. It was to have been the site for The Spiral, Daniel Libeskind’s above-ground scheme, which had received planning permission, but in recent years the shared space of Exhibition Road was developed, which has effectively turned the V&A 90 degrees towards the street and plans to build The Spiral were abandoned.”

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The Aston Webb screen prior to its removal

“We placed the gallery below ground, with support spaces in the second basement. The courtyard could then become a place for people to drift into from Exhibition Road and eventually connect with the Madjewski Garden. We worked with the planners to build a case to open up the Aston Webb screen, to create a veiled transition between the street and courtyard.”

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Secant pile wall and temporary props (ph: AL_A)

“We had a secant pile wall and in the centre of the site 1200mm diameter bearing piles both support the gallery floor and hold the basement down, compensating for the weight of the excavated soil. The piling continued all around the perimeter and we had to prop the basement walls to prevent them from moving which would cause damage to the surrounding buildings. We were piling within 300mm of some of the cornices in order to maximise the available gallery space.”

Five rooms were knocked together for the Blavatnik Hall, and a void created for the staircase that passes under the facade (ph: Stephen Citrone)

“We used a semi-top-down construction process for the gallery floor slabs eleven metres down, so that rather than put in extra props at gallery floor we excavated underneath the floor. A dog-leg area of more traditional construction contained all the services and lifting equipment. The next stage was to build the courtyard structure, spanning 30 by 40 metres to give a clear floor plate underneath. A storey-high truss spanned from Exhibition Road back to the museum, plus ‘toblerone’ trusses which created the triangular profile of the ceiling. Once the steel was in we could put down metal deck and pour the concrete floor slabs, which also prop the basement walls.”

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Arrangements of the courtyard’s bespoke ceramic tiles were designed to loosely reflect the structure below

“We wanted to have the possibility of natural light in the gallery, when non-light-sensitive objects were to be displayed, so we cut an oculus into the courtyard. This was also, together with the surface of the courtyard, part of making the invisible visible, to draw visitors into wanting to know what was beneath. Ten different tile patterns were designed for the ceramic tiles of the courtyard, which were then laid in such a way as to loosely reflect the structure of the folded roof below, revealing it beneath the feet of the visitors.”

The staircase passes beneath the facade, which is expressed in the colour of the supporting columns (ph: Hufton & Crow)

“Other spaces were designed to try and create a relationship between above and below, to weave the gallery into the existing fabric of the V&A. The changing level of the folded roof allowed a subtle variation in ceiling height and give an illusion of a higher space. It also allowed the integration of services – lighting, ventilation, smoked detection and hanging points. The structure is revealed through the oculus, as in a vitrine. The descent to the gallery begins within the existing building, the newly-created Blavatnik Hall, and with a view through to the Madjewski Garden. The staircase passes beneath the facade, which is expressed in the colour of the supporting columns . At the foot of the stairs is the surprise of daylight, and materials were chosen to reflect that light.”

David Tompson, Associate at Nicholas Hare Architects on the new Student Centre at University College London, completed in 2019

The Gordon Street facade (ph: Alan Williams)