Reconstruction in tight urban locations amidst existing underground infrastructure presents numerous challenges. As described in a recent column, engineers and designers in the U.K. are becoming adept at overcoming these obstacles.
Another example of British ingenuity is a new housing project for students attending the London School of Economics in central London.
The 12-storey building, developed by Dominus and constructed by McAleer & Rushe, will sit in part over an abandoned railway station. Once completed, it will offer housing consisting of 669 bedrooms, 35 per cent of which will be affordable, as well as community facilities at the ground-floor level.
There were challenges from the start. The site was occupied by a mid-‘50s building constructed prior to the railway line being operational. As a first step, the structure was demolished in 2020.
This posed significant safety challenges for specialist engineering contractor McGee, given the building’s close proximity to neighbouring properties at the junction of Holborn Viaduct and Snow Hill, an active area of London’s financial district.
However, the new project held significant promise and thereby gained the support of the City of London government. First, the plan preserved the characteristics and composition of strategic views of important landmarks of special architectural, historic and heritage significance as outlined in the London View Management Framework.
Secondly were the numerous positive community benefits.
“The proposed development provides the opportunity for the influx of a new demographic of young people housed in the student accommodation,” the city said. “The site’s close proximity to the future location of the Museum of London at Smithfield and Culture Mile, the proposal on this site would help to cultivate the transformation of the area to a culture quarter of the city.”
Yet, there remained significant engineering challenges. Driving piling foundations for the mid-‘50s building had been relatively straightforward before the railway station was open. However, this was no longer an option for the new project.
“It was quite complicated and constrained and almost impossible to build this building using traditional construction methods,” explained Anupriya Rajpal, development director at Dominus.
For example, the railway tunnel’s precast plank roof from the 1960s, installed as part of the original building’s construction, could not take the weight of a piling rig.
In addition to the abandoned Snow Hill railway station and tunnel underneath, the location is further constrained by additional underground infrastructure. This includes the Central subway line that continues to run close to the site, an unused post office railway tunnel, plus City of London underground service viaducts that house electrical and data cabling.
As a result, the foundations for the new 12-storey building will require a radical yet surprisingly simple old-school approach.
As described in Building.com, five caisson piles, each 20 metres deep, one-metre in diameter and five metres apart, will be hand-dug in a line along the railway platform on one side of the site. It is proposed that two workers, equipped with shovels, will place excavated material into a bucket which will then be hauled out using a rope and pulley and deposited onto a conveyor. The bucket is lowered again for the next load.
These five piles will expand in diameter to as much as five metres at their bottom and will be filled halfway with cement with steel reinforcement for the top half. Steel trusses will span the railway line over to a conventional foundation on the other side of the site, thus supporting the building above.
Since there is still an underground subway running alongside the building, large rubber bearings between the concrete columns and steel structure on both sides of the building will mitigate vibrations that might be felt by occupants.
In addition to the bedroom accommodations, the team of Stiff + Trevillion Architects and Jonathan Cook Landscape Architects have targeted BREEAM Excellent for the finished structure, with the intention to be sustainable in both construction processes and operation. Elements such a unitized façade and modular bathroom pods will be manufactured offsite. Measures to reduce operational carbon emissions include urban greening and various water saving measures.
Once complete, Dominus says the project will provide student residents with an onsite cafe/bar, cinema room, music rooms, games area and gym. The 500 long-term and 32 short-stay cycle parking spaces will be available to both students and the community. The general public will be able to access the roof terrace in order to enjoy wide views of the city eastwards towards St. Paul’s Cathedral.
John Bleasby is a freelance writer. Send comments and Inside Innovation column ideas to editor@dailycommercialnews.com.
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