Operation Umbrella: Rebuilding Oxford Circus
As the Victoria line celebrates its 50th birthday, we look at a largely forgotten triumph of transport construction: Operation Umbrella.
On the August Bank Holiday in 1963, London’s busy Oxford Circus and the surrounding streets were closed off. The streets were empty of weekend shoppers and all traffic. In their place a team of engineers and construction workers take over.
“Civil, mechanical, electrical, signal, and telegraph engineers. Railway operators, consultants and contractors, architects and designers combined their talents and their experience. They called upon a number of traits, crafts, skills and specialisations to put their plans into practical shape. They were backed by brawn and by brain. Thus they built the Victoria line. The first but not the last of London’s new tube railways.”London’s Victoria Line, British Transport Films 1969
Working meticulously to a detailed plan they build a raised platform, lifting the Circus a metre. Within sixty-five hours they complete the ‘Oxford Circus Umbrella’, the raised platform and four ramps from each of the road approaches to the junction.
The Bank Holiday weekend effort was part of Operation Umbrella: the scheme to add the Victoria Line to Oxford Circus station just below the junction, whilst keeping one of London’s busiest stations and junctions moving.
The construction of the Victoria line ‘was one of the most difficult and complex engineering projects ever undertaken’ says the book The Victoria Line: A Pictorial Record published by London Transport for the line’s official opening by Queen Elizabeth II on 7 March 1969. Specifically, the greatest challenge was building the elements close to the surface: where stations with spacious ticket halls and tangential escalator shafts had to be dug. London’s subsurface was congested: a warren of utility services and building foundations.
Creating a coherent network
Another challenge was minimising the impact of the construction on rail services and road traffic. The ambition with the Victoria line was to connect the disparate patchwork of Underground lines London Transport had inherited into a connected network. All Victoria line stations (bar Pimlico, which was a late addition to the route) would offer interchanges to existing Underground or main line rail services.
This meant construction would take place close to existing rail tunnels and at busy road traffic intersections. At five key stations, the new platforms were to be same-level interchanges, such as the parallel northbound platforms on the Bakerloo and Victoria line at Oxford Circus. This station design feature was to ease interchanging, reduce passenger movements through stations and ease rush hour traffic. However, creating same level interchanges was complicated: rail services had to be diverted and platforms relocated so that northbound or southbound services of two London Underground Lines could be matched.
The Victoria Line was the first line to be built in 50 years. Plans for Underground network expansion lay dormant for years during the Second World War and the rebuilding efforts afterwards. The new line from Walthamstow to Victoria received Parliamentary approval in 1955, but it was not until August 1962 that central government authorised construction of the line to start. The extension to Brixton was approved in August 1967. “The complex task of creating a new tube railway has to be carefully planned so that the engineering works were carried out with the least possible interruption to existing Underground services and with minimum disturbance to properties, the public and road traffic“ a leaflet from 1969 informing passengers of the new Victoria Line reads.
Getting down to detail
The nearly seven years between Parliamentary approval and building work starting gave London Transport the chance to methodically plan the engineering works. In particular, how to create same-level interchanges between different lines at the stations. The footprints at existing stations had to be enlarged or altered to make the extensive interchange network possible.
Despite detailed planning and efforts to minimise the construction duration, it took over six years to build the 17km route from Victoria to Walthamstow. Construction of the line included many difficult elements such as complicated station redesign and route diversion to accommodate same-level interchanges. However, it was the complexity of the work at Oxford Circus that limited the pace of construction in Central London. Although the first contract let following the government’s go-ahead on the Victoria line was for Oxford Circus station, the station was also the last major work to be completed.
Until 1963 work on ‘one of the most complicated engineering projects London has ever known’ (as a station leaflet from 1968 described the Victoria line) had mostly gone unseen by the public, deep below ground. Exploratory work beneath the existing Oxford Circus station began in September 1962 to establish the position of water mains, pipes and other utilities.
Reconstructing Oxford Circus
The reconstruction of Oxford Circus station exemplifies many of the challenges civil engineers still face when carving stations out of London’s congested underground.
It was certainly the biggest station reconstruction as part of building the line. The design included a new ticket hall directly beneath Oxford Circus junction, new sets of escalators to the intermediate and then low concourses as well as new platforms and interchange passageways.
To make things even harder, Oxford Circus was one of London Underground’s busiest stations – then as it still is today. Above ground Oxford Circus was also one of the city’s busiest junctions. For these reasons London Transport had to find a novel way to work that would allow both the station and road junction above to remain fully operational while construction began on the required new elements below the surface.
How to keep one of London’s busiest traffic junctions running smoothly while constructing a spacious new Underground ticket hall inches beneath it? The answer was Operation Umbrella, a steel umbrella bridge that would carry road traffic and allow construction of the new Underground ticket hall below it.
The moment of truth
Operation Umbrella was implemented on the August Bank Holiday weekend of 1963. Oxford Circus and adjacent streets were closed from early afternoon on Saturday until 6.30am on Tuesday 6th August. The Oxford Circus umbrella was a platform roughly a metre above the road surface. Ramps from all four directions lifted road traffic to the raised junction. The deck was assembled from prefabricated steel sections supported by a steel framework that itself rested on 25 concrete foundation piles.
The foundations for the umbrella were installed around Oxford Circus under the cover of night, over 18 nights ahead of the 1963 August Bank Holiday. These foundations had to be threaded through a maze of cables, gas mains, water pipes and sewers – missing some of them by as little as an inch. The foundations the umbrella rested on were 25 concrete cylinders with a bell-shaped footing in the clay ground. The cylinders were made by drilling holes, one-metre in diameter and up to 15 metres deep, then lining the holes with a steel pipe, and finally filling the pipe with concrete.
<bThe plan was to build the whole umbrella bridge in one long weekend August Bank Holiday 1963 – come what might. The circus had to be open for traffic by 6.30am on the Tuesday morning. There were just sixty-five hours to do the job. It was raining – of course. The first girder went into position on the Saturday in less than two hours after starting time that night. It was thirty-five feet long and just over five tonnes.’London Victoria Line (1969) documentary
A steel framework was constructed upon the concrete foundations. It would hold the prefabricated steel sections in place to created a continuous bridge for road traffic to travel over. The Operation Umbrella team took over Oxford Circus at 1.30pm sharp on the August Bank Holiday Saturday and over the course of the afternoon the steel framework was put in place. At 7pm that night, the night shift took over and started putting the first decking sections into place. In total, 254 sections, weighing over six hundred tonnes, were fitted. On average it took the team just eleven minutes to put each decking section into place. The whole structure was designed to interlock and thereby stay in position. Once the decking was bolted down the asphalt was laid. Right on schedule the site was ready for regular traffic to resume at 6.30am on Tuesday August 6th 1963, after the August Bank Holiday.
With the umbrella in place the new ticket hall and the upper escalators were excavated. Materials were delivered to the working site over night by removing decking pales and lowering them through the holes in the decking. This decking was then replaced to allow normal traffic to resume in the morning. The new ticket hall ceiling would be only around 75cm below the road surface. Utilities crisscrossed where the new station would be were rerouted. Once the new ticket hall roof was completed the load of the roadway above was transferred from the ‘umbrella’ to the new ticket roof.
To add to the complexity and difficulty of reconstructing the station, the new southbound Victoria Line station tunnel passed just under the large Peter Robinson department store at Oxford Circus with its three basements and its foundations. It was necessary to spread some of the building’s load before tunnelling began. From the working shaft at Cavendish Square, a 230m access tunnel was dug to beneath the department store. A pre-stressed concrete raft was then constructed below the basement to spread the load. The under-side of this raft was formed of weak concrete as the new southbound tunnel would cut across the underside of the raft itself.
Digging by hand
At Oxford Circus, as all stations along the Victoria Line and sections with difficult ground conditions, miners in tunnelling shields cut the clay with power-driven hand tools. In November 1965 the station tunnel shield came into contact with the curved underside of that raft. Work had progressed smoothly enough that the miners had only to skim off the very bottom of it. The new 7m in diameter station was then fitted with specially reinforced steel tunnel rings that could bear the load of the department store and its basements above.
Three years later, on the August Bank Holiday 1966, the umbrella was extended 30m eastwards along Oxford Street to enable the construction of a subway linking the existing ticket hall to the new one.
A successful end
After nearly five years of service, the ‘Oxford Circus’ Umbrella was dismantled by a team of civil engineers on Easter Bank Holiday weekend in 1968. Operation Umbrella had been completed. The Victoria Line itself opened in stages. Without ceremony services between Walthamstow and Highbury & Islington started mid-afternoon on the 1 September. On 1 December 1968, services extended to Warren Street station in Central London.
Finally, the Victoria Line was officially opened on 7 March 1969 by the reigning monarch Queen Elizabeth II, opening to the public at 3pm that afternoon. The extension to Brixton was signed off in 1967 and opened in 1971. Pimlico, a late addition to the line and the only station without any interchange, was opened in 1972, completing the Victoria Line route as we still know it today.