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Bam put through Oxford University underpinning exam

A Grade II-listed facade is all that will remain at Keble College’s new accommodation and research site.

Project: The Acland Project
Client: Keble College
Contract type: JCT Traditional
Region: South-east
Main contractor: Bam Construct
Concrete frame subcontractor: Getjar
Architect: Rick Mather Architects
Start date: September 2016
Completion date: September 2018

“I think it looks like a doll’s house now,” says Bam Construct project manager Alec Carr.

He’s referring to the preserved Grade II-listed structure that sits up in the air, marooned on piles and a transfer slab in the middle of a site where all the other structures have been demolished (see box).

The plot was formerly home to the Acland Hospital until it was bought by Oxford’s Keble College in 2004 and converted into student accommodation.

The element of the site pointed out by Mr Carr is the handsome central section of the old nursing home, now supported on its piled ‘stilts’. 

The structure was an early career design by architect Sir Thomas Graham Jackson, also known as Oxford Jackson for his landmarks across the city that include the Bridge of Sighs and the Examination Schools.

Bam initially got onto site in February last year to give it a second – and far more radical – makeover.

Bam Construct Keble College 5

Bam Construct Keble College 5

The Grade II listed centre-piece of Acland House sits on a load transfer slab

This will provide a 250-bed accommodation with kitchen, refectory, gymnasium and a lecture theatre. Below ground things get a little more interesting with autonomous vehicle as well as robotics research laboratories in a basement that spans the entire site.

Having delivered the early works package, Bam then won the main contract, for which it commenced work the following September.

Archaeological interruption

However, things haven’t been quite as simple as that.

Eight months of planned archaeology, which wasn’t mentioned in the information Bam received and therefore wasn’t accounted for in the programme, meant the contractor needed to have a rethink to get works back into the available timeframe.

And it wasn’t a small investigative dig either.

Encompassing the entire footprint of the project to at least 2 m deep, it then reached down a further metre at one edge. Mr Carr says that at the deepest point the archaeologists had found some ‘old rotten timber’ and thought it might be defensive components from the English Civil War.

Bam Construct Keble College 4

Bam Construct Keble College 4

The new structure features a reinforced concrete frame

With Oxford being a loyalist town that sheltered Charles I, and the site being on the boundary of the inner city that featured a rampart at the time, hopes were pinned on the ‘discoveries’ from the deeper dig on the south side of the site.

“A 3 m dig there gave us a problem with earthwork support,” Mr Carr says. “So we said, ‘If we can start demolition [of the student accommodation] early, decant the students out and then start the piling early, we could use this as the first support for the archaeological works’.”

“All we found was a couple of wells, two dead horses and some little quarry pits”

Alec Carr, Bam Construct

He explains that this shifted the eight months of investigation into the early works allowing for the main contract to begin on track in September for its 118-week programme. “So we’re back on track,” he says.

“At the end of the day, nothing of value was found. So archaeologists: very disappointed; client and us: quite happy,” he says with a grin. “All we found was a couple of wells, two dead horses and some little quarry pits.”

Preserving Acland House

The most technically demanding aspect of the job relates to the retention of Acland House and building a basement under that (see online animation). “All we’re really doing is façade retention but effectively we’re keeping three rooms and four floors and a listed staircase,” Mr Carr says.

Bam has retained more at the back of the structure initially to keep it all stable during the bulk excavation. Site workers achieved the underpinning works that allowed for the excavation below via a temporary stooling system comprised of 450 mm diameter reinforced continuous flight auger piles that go down 12.5 m, penetrating the ground for about 8 m of that length.

This meant operatives could form a reinforced concrete transfer slab beneath the building that, through the use of dry-packing, meant the building could be re-seated on its foundations. A propping system at the front of the building offers additional support, with the transfer slab tied into the secant wall at the rear to keep it all restrained.

Once the basement slab has been formed, the onsite team will form the new walls and then transfer the building’s load onto these, before breaking out the stool foundations.

“Part of the challenge was that we had another 5 m excavation in front of the Acland building for both storm and foul-water attenuation,” says Mr Carr. “Everything goes into various holding tanks in the basement before being pumped back out and then it’s gravity fed into the sewer.”

This meant that sequencing required some very careful thought for works to continue efficiently across the site.

For the basement, Bam is providing Keble College with a shell and core, having excavated the whole site with a 5 m-deep bulk dig, well beyond the area of the few small basements that had served the original building.

“It breaks my heart that we are going to have to break out part of the secant wall”

Alec Carr, Bam Construct

One such pre-existing basement was located beneath the retained listed façade.

There’s a pleasing balance to the scheme that sees this part of the old building playing a central function. Rather than just providing aesthetic appeal, alongside providing accommodation, it will also house a car lift that will transport vehicles to the driverless technology research lab.

Heartbreak

Simplex Westpile won the contract to support the edge of the archaeological dig and installed a secant piled wall around the site’s perimeter to form a dry box for the basement excavation.

“It breaks my heart that we are going to have to break out part of the secant wall [to allow the structure to pass through it],” Mr Carr says. “We tried to convince the client to keep it. I think it didn’t want the design responsibilities,” he adds, referring to what would happen if the wall had become part of the eventual structure rather than a separate element.

Bam Construct Keble College 2

Bam Construct Keble College 2

The new basement extends across the entire site

The rest of the foundation work, visible at the time of CN’ s August visit, consists of a raft of varying thicknesses, though generally 600 mm to 900 mm. This will bear a reinforced concrete-framed structure that will take shape on four sides around a central quadrangle, in a design that broadly follows the structural footprint of the former Acland Hospital.

The team is relying on the weight of the raft to resist uplift from the water table, which begins at about 4.5 m depth.

Project peculiarities

“In terms of logistics, we can only feed the job from the north side of the site,” Mr Carr says. “We’ve got less than 3 m on the boundary so it’s like a job in London in effect. We’re out in the sticks here so we make a bit of a meal of it.”

It might not be a standard job for Oxford in terms of logistics, but it’s also a different kind of job for Mr Carr.

“It’s been a change in mindset for me – I’ve been design and build, and PFI for the last 10 years,” he says. “We’re now having to work with the client team and they’re very much in charge. Keble are pretty hands-on.”

He says the client has aimed high with the designer. “Rick Mather Associates is quite a signature architect. They did the Ashmolean [Museum] and various jobs on this campus.”

Bam Construct Keble College 15

Bam Construct Keble College 15

Acland House required careful underpinning to allow basement excavation (see animation)

The envelope is a mixture of structural steel framing and brickwork, but this façade is particularly fiddly. Given the client’s desire to retain the heritage aesthetics in the new development, RMA opted for handmade bricks to blend with the retained Oxford Jackson portion. Which is all well and good, but the thing about handmade bricks is a deliberate lack of continuity.

“It’s a 40 mm-deep brick on lime mortar… it’s awkward,” Mr Carr says. “It’s one of RMA’s signatures,” he says, adding that it’s been used on a lot of Keble’s modern buildings. “Generally it’s brick-clad with a mixture of curtain walling and punched windows, with a zinc roof.”

The emergence of the façade is imminent with work on its structural steel frame due to begin at the end of last month [August].

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It’s an uncommon job in a variety of ways, including the lack of BIM on the project.

“We don’t even have a 3D model; the architect won’t give us access to theirs, so it’s quite challenging,” Mr Carr explains. “Everybody works in .dwg [files] or CAD – and we get all our drawing information issued to us on a PDF.

“We don’t even have a 3D model; the architect won’t give us access to theirs”

Alec Carr, Bam Construct

“Anybody that’s a got a design element [to do] wants a .dwg type drawing to be able to use it as a baseline to do their design and it’s quite a challenge sometimes to get that information out [to the designer, from a PDF] electronically,” he says. “Generally we persuade the architect or the structural engineer to give us a .dwg.”

From archaeological delays to retained listed buildings to tricky handmade brick façades – and much in between, the Acland Project certainly hasn’t been without its challenges.

But when students arrive for the beginning of the academic year next September, they’ll be able to live, eat, study and research robotics and autonomous vehicles all at Keble College’s newest ‘heirtage’ site.

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