London’s Farringdon station has been given an overhaul and is ready for more passengers, bigger trains and Crossrail. But it hasn’t been an easy ride - and digging a 140m tunnel by hand was the least of it. By Thomas Lane. Photography by Colin Streater
This weekend marks a major milestone for the capital’s two biggest transport infrastructure jobs. From tomorrow 50% longer trains will start running on the Thameslink service linking Bedford to Brighton. Adding four carriages to the existing eight carriage trains has meant lengthening the platforms at 14 stations along the route. The second major milestone is that the first Crossrail-ready ticket hall opens on Monday at Farringdon station; this will serve existing Thameslink and London Underground services and Crossrail passengers from 2018.
Longer trains and extra passengers meant Farringdon station needed a major upgrade. The only access used to be through a ticket hall built in 1863 serving two Underground and two Thameslink platforms; this had to be frequently closed during peak hours because of overcrowding. Passenger numbers will jump again in 2018 with the arrival of Crossrail and an increase in Thameslink services from 16 to 24 trains an hour. A total of 140 trains per hour will run through the station once Crossrail and Underground services are added in, making it one of the busiest interchanges in London. The solution is an upgrade of the existing station including longer platforms, a new ticket hall and a third entrance. Building this in a very constricted central London site has been a major challenge.
I call it Clockwork Orange as the whole job is about planning
Keith Morgan, Costain
On the site meeting room wall is a large plan view of the project covered in coloured boxes of text detailing all the work that has to be done in the week ahead. “We call it the bubble chart as it literally runs the job which is incredibly complex and has to be done in a very short period of time,” explains Keith Morgan, contracts director for Costain which is doing the work in joint venture with Laing O’Rourke. The contractors are doing the work for Network Rail which is responsible for the Thameslink and Underground works plus £40m worth of work for Crossrail. Morgan explains there is a traffic light system, a green box means the task has been completed, amber means the job is running on that week and red means it is behind schedule. “We find the bubble chart is a really simple way of running the project as everyone knows what they are doing.”
Finding space for longer platforms was difficult due to the constrained site. The station sits in the valley of the Fleet river and is boxed in on either side by brick arch retaining walls needed to hold back the roads and buildings on either side. This made widening existing platforms impossible. The lines immediately north of the station drop down into tunnels, one of the steepest inclines on the rail network. That meant the platforms had to be extended south but existing structures were in the way and had to be moved. All this work has been done without disrupting Thameslink and Underground services or inconveniencing neighbours and the thousands of commuters using the station every day.
The job includes lengthening the Thameslink platforms and upgrading the existing station to increase its capacity. This included rationalising access routes through the station and adding a bigger footbridge across the platforms and more stairs. Passengers were huddling under a short section of roof over the platforms in bad weather so this has been extended to create a larger dry area. The new integrated ticket hall has been built on the south side of Cowcross Street opposite the existing building. Extra power was needed for the station systems so a new substation has been built at the north end of the station.
The only way to get all this done in time for the Olympics is to work 24 hours a day, seven days a week, 365 days a year. At night the power is switched off giving a window of three hours to work on the underground side of the station and four hours for Network Rail. Over 100 workers line up along the platform in their distinctive hi-vis orange ready to start work the minute the power is shut down. “I call it Clockwork Orange as the whole job is about planning,” laughs Morgan. He says there are regularly 500 people working on the station at weekends and describes Christmas as his busiest time of year. Morgan is proud of the fact that the station hasn’t been handed back late once to the operators at the end of night and weekend shifts.
Minimising disruption has meant some extreme construction techniques. A route was needed for the high voltage cables running from the new substation to the north down to the integrated ticket hall to the south. “We had to dig a 140m long tunnel under platform one by hand so we could keep the station live,” says Morgan. “It was the only route available on the project.”
We’ve done a lot of things so Crossrail can come in and just drive its tunnels through
Richard Walker, Network Rail
Richard Walker, programme director for Network Rail, describes extending the Thameslink platforms south as a “massive task and the most complex engineering challenge on the job”. The platforms had to be extended under Cowcross Street and underneath the new integrated ticket hall. “The work meant demolishing the Cowcross Street bridge as the abutments were in the way of the new platforms,” explains Walker. The existing station exits onto Cowcross Street and is used by thousands of commuters a day so had to be kept open while the bridge was demolished and the new one built. To complicate matters further the bridge also supported the ticket hall so this had to be underpinned at the same time.
The only way to maintain pedestrian flows along Cowcross Street was to rebuild the bridge in two halves. The existing station was supported on temporary works which enabled the old bridge to be demolished. With the bridge out of the way new piles were sunk followed by new abutments that were sufficiently wide enough apart for passengers to pass along the platforms. Two sets of columns were built on the platform edges and concrete-encased steel beams craned in to link the abutments on either side of the station to the set of columns. Finally, long beams spanning between the two sets of columns were craned in over the tracks.
The process was repeated for the second side of the bridge and a 26m long beam craned in to support the existing ticket hall. Once the loads were transferred onto this beam the temporary works could be taken down. Again the job took meticulous planning. The concrete encasing the beams, a London Underground fire proofing requirement, was done offsite to minimise disruption. Just moving the temporary hoarding used to separate pedestrians from the work took months of preparation. “Every time you want to move the hoardings you need approval from the fire authority, which includes modelling the passenger flows,” explains Dan Powrie, Costain’s construction director. “You need to allow two months to get the approval. We’ve moved the hoardings in Cowcross Street about five times to keep everything moving.”
The existing station has also been upgraded to cope with extra passenger numbers. As much clutter as possible has been removed from the platforms to create more space. A new footbridge forks in the middle to create two spans which helps move more people over the platforms. An 800 tonne crane, Britain’s biggest, was needed to lift this into position. There are now six sets of stairs in the existing station rather than the previous three. One of the most significant jobs was demolishing a row of shops on Turnmill Street, which runs parallel with the station, and building a new covered concourse linking the north end of the station to the existing ticket hall. This includes a new entrance at the north end to help smooth passenger flows at peak times.
The roof over the platforms has been extended using 34m long prefabricated roof sections, again to minimise disruption. These sit on new columns so the roof is independent of the existing structure. Structural steel specialist Bourne Steel and roofing specialist Lakesmere collaborated on the design and construction of the roof sections which consist of structure, cladding, louvres and roof lights. The sections were lifted into position at weekends with a 500 tonne crane.
The integrated ticket hall sits over the newly extended platforms and had to be redesigned to accommodate Crossrail passengers once this got the go-ahead. With Network Rail taking responsibility for all three services it means subsequent Crossrail work will interface seamlessly with the current works. “Once Crossrail got the go-ahead we made the platforms wider and redesigned the entire foundations and the way the ticket hall is formed so there is no impact on those Crossrail running tunnels,” explains Walker. “We’ve done a lot of things so Crossrail can come in and just drive its tunnels through.”
That work included demolishing a 12-storey building next to the integrated ticket hall, which creates the space for the rest of the Crossrail station. The work also included diverting the River Fleet, which runs in a tunnel, around the new ticket hall. The piles supporting the ticket hall are sleeved to accommodate any disturbance caused by the Crossrail tunnel boring machine, the new Fleet river tunnel has also been designed to allow for movement.
A 600 tonne crane was taken to pieces and dropped down into the space occupied by the demolished building. The crane was needed to lift the huge, 60 tonne beams that span the railway tracks and form the base of the ticket hall.
Once the beams were in place the rest of the building structure and prefabricated roof could be completed. The building includes two lifts serving the Thameslink platforms below. The 22m deep lift shafts will also serve Crossrail once the underground part of the station has been built. “We’ve had to put stops on the lift otherwise you just go down into a hole,” says Morgan. Crossrail escalators will be built to the side of the ticket hall and a section of cladding removed in 2018 to connect two together.
The revamped station opens over the weekend but the job isn’t finished yet. Opening the new ticket hall means the existing one can be closed and refurbished, this will reopen on 6 February. The lifts down to the platforms will start operating in April. The project team will be working flat out over Christmas to ensure all this work is done before the Olympics so spare a thought for Morgan, Walker, Powrie and their colleagues while you are enjoying your mince pies and Christmas pudding.
The completed integrated ticket hall is only a small part of the job of building Farringdon’s Crossrail station. There will be two exits, the first on the western end of Crossrail’s platform tunnels at Farringdon and the other at the eastern end at Lindsey Street near the Barbican. This station will also serve the Underground.
Piling for the station boxes which will contain the escalators and services has already commenced on both sites. The main contract, worth up to £400m to build the stations, has just been awarded to a joint venture of Bam Nuttall, Ferrovial Agroman (UK) and Kier Construction. These works will start in late 2012.
The platform tunnels are formed by sinking a shaft at the eastern and western ends. A tunnel boring machine is lowered down the western shaft and travels 400m to the eastern shaft. It then travels west again to form the second platform tunnel.
The machines used to bore the east and west sections of the Crossrail lines also meet at Farringdon. The tunnel boring machine boring the western section arrives at the eastern side of the station in late 2013 and will be dismantled and taken out via the ticket hall. The two machines used for the eastern section arrive a year later and will be dismantled and taken out back through the tunnels.
Client Network Rail for London Underground and Crossrail
Principal designer Atkins
Contractor Laing O’Rourke/Costain joint venture
Demolition and piling Expanded Group
Structural steel Bourne Steel
M&E VVB Crown House Joint Venture
Station roof Lakesmere
Ticket hall cladding Astec
Internal fitout MPG
Architectural metalwork Robert Stevens and Sons/Delta fabrications