The £14.8 billion Crossrail project is now progressing at a pace. The route from Maidenhead and Heathrow in the West to Shenfield and Abbey Wood in the East will run through 21km of twin-bore tunnels up to 40 metres below the ground. More plans have recently been submitted for a new station at Abbey Wood and for property development at Farringdon. There is now even a short list of bidders competing for the privilege of running the prestigious Crossrail service when all the work is completed in 2018.
The new route will pass through 37 stations. A number of these are currently experiencing huge change involving complex engineering challenges, usually in very confined conditions.
Liverpool Street is a good example of this. The new Crossrail station will be located between the existing Liverpool Street and Moorgate stations. The programme of building work includes two new entrances and ticket halls, creating new interchanges with the Northern, Central, Metropolitan, Circle and Hammersmith & City lines, as well as connections to Stansted Airport and National Rail Services. The Rail Engineer recently visited the site to see how this complex project is progressing.
TBM break through
In 2012, tunnel boring machines (TBMs) Elizabeth and Victoria started to work their way toward Liverpool Street station from Limmo Peninsula to the east of Canary Wharf. They are now working westward, creating new tunnels that will eventually approach the Liverpool Street station site, and will break through into the pre-constructed underground tunnels that are currently being built to accommodate the platforms within the Crossrail station.
There, the TBMs will undergo any essential planned maintenance before moving on, breaking out of the station tunnel to complete the 8.3km twin-bore tunnels to Farringdon East. The TBMs are expected to pass through the Liverpool Street station site in the autumn 2014.
Much of the work currently taking place is in preparation for the passage of Elizabeth and Victoria through the site. Troy Easthorpe is Crossrail’s project manager for Liverpool Street station and Colin Niccolls is project manager for the station tunnelling work. Troy explained that the Liverpool Street Crossrail station is currently divided up into four main sites.
Platforms and concourse
The first site is down a 42 metre temporary shaft which has been constructed in the middle of Finsbury Circus. This work forms part of a £300 million contract let to the BBMV joint venture – Balfour Beatty, Alpine BeMo Tunnelling, Morgan Sindall and Taylor Woodrow.
The shaft provides the node point for the construction of separate tunnels forming the east and west platforms, a central concourse tunnel running the length of the station and a number of cross passage link tunnels between the concourse and platform tunnels. Colin explained that in total there will be more than 1.5km of tunnels. So far, they have constructed more than 600 metres built at a rate of five to six metres every 24hrs.When completed, the platform and concourse tunnels, plus passages, will link the new eastern and western ticket halls that will be constructed at Moorgate and Liverpool Street.
The 42 metre deep shaft increases from 12.5 metres diameter at the top to 14 metres diameter at the bottom. There are four six-metre diameter pilot tunnels constructed that lead from the shaft. Each tunnel has a temporary sprayed concrete lining. These pilot tunnels then enable excavation to start on the 250 metre long platform and concourse tunnels and the diameter is eventually increased to 9.5 metres diameter after which a waterproofing membrane and a secondary shotcrete lining will be applied to complete the structural work.
Although this work is expected to be completed by 2015, the platform tunnels must be ready to accept the arrival of TBMs Elizabeth and Victoria in the autumn of 2014 to ensure that the overall programme is able to keep to the critical path. Colin was definitely pleased with the progress that they are making but emphasised that, in tunnelling, one always has to keep one step ahead – testing conditions and anticipating potential problems before they materialise. The site is closely monitored for ground movement and there is an array of underground tubes installed to allow compensation grouting when required.
When the work is completed, the Finsbury Circus area will be restored to its original state and it will look as though nothing has ever happened.
Moorgate ticket hall
Construction of a new western ticket hall for the Crossrail station is well underway at Moorgate. The £30 million contract was awarded to the JV Bam Nuttall and Kier and, as Troy pointed out, it was evident that this is a very confined site. The work involves the construction of a shaft 55 metres deep which is being excavated next to the existing Moorgate Underground station which has the Hammersmith & City line to the north of the site, the Northern line to the east and the existing Moorgate station ticket hall nearby.
Simon Williams is the site manager for Crossrail, and he explained that the shaft is being excavated next to the existing station with reinforced concrete panels installed 60 metres below the surface to form a diaphragm wall box below ground. This work is now complete and two Liebherr HS 855 crawler cranes, fitted with hydraulic grabs, are currently employed constructing 30-60 metre deep temporary strutting walls in short three- metre sections. They are using bentonite clay to minimise ground water penetration before reinforcement and concrete provides adequate displacement.
This part of the contract is only required to enable the westbound TBM a path through the site – the eastbound TBM bypasses the site altogether. Once the TBM has passed through the site, the ground will be excavated down to the required level and the strutting walls will be demolished. All the spoil will then be carted off to Wallasea Island to form a bird sanctuary, along with 4.5 million tonnes of spoil from other Crossrail sites. Following this and some more additional piling to stabilise the site, work on the new ticket hall will commence.
As deep as Nelson’s column
Also part of the Liverpool Street station site is the Blomfield Box – a 40 metre deep structure to accommodate ventilation, electrical, mechanical and systems equipment for the new Crossrail station. It is part of a £130 million contract awarded to Laing O’Rourke which is also responsible for the construction of both stations and the platforms and central access passageways. Chris Goatman is the site manager for Crossrail and Malcolm Nelson the project director for Laing O’Rourke.
This is another incredibly cramped site situated alongside the Broadgate development. Chris explained that they had already driven sixty-seven 1.2 metre diameter reinforced concrete piles to form a perimeter box. In addition, they are in the process of driving a further fifteen 1.5 metre diameter piles to support the floor slab when the excavation is completed. This will stop the box from floating, a distinct possibility due to potential ground water pressure even though the box weighs 10,000 tonnes!
Malcolm was also keen to point out that the box will be deep enough to comfortably house a column dedicated to his namesake.
More 300mm reinforced concrete piles have been driven around the site to protect the adjacent existing buildings and ensure that all is stable so that neighbours will not be affected by the work. Troy pointed out that Crossrail devotes a considerable amount of time to its neighbours, keeping them informed about progress, new work, possible road closures and progress of the TBMs.
He also indicated that so far there have been no delays to train services or impact on local communities even though, at this particular location, they are constructing a box formed from the deepest pile shaft with 40m long piles, containing 22 tonne reinforcement cages, that have been constructed less than three metres away from live London Underground running lines. It is something that he and his team are clearly very proud of and with some justification.
So far, over 250 piles have been completed including all high-level foundation works and two thirds of the main shaft piles installed up to 50 metres deep, making the box Crossrail’s deepest piled shaft. The main shaft piling is now almost complete.
Utilities, systems & equipment
Adjacent to the box, a new Communications Equipment Room (CER), power substation and switch rooms for the Liverpool Street London Underground station are being constructed as part of a £23 million contract awarded to Taylor Woodrow. This will allow the demolition of the existing substation to create space for the Broadgate ticket hall on Liverpool Street. The power substation and switch rooms are due to be completed later this year.
Other works include a new 53-metre-long cable tunnel which has now been completed five metres below the ground and it is connected to the new substation. It is the first permanent sprayed concrete lining tunnel to be finished on the Crossrail project.
The fourth site is at Liverpool Street which will house the Broadgate ticket hall. Prior to Laing O’Rourke constructing the new sub-surface ticket hall, Taylor Woodrow is busy clearing the area by diverting all of the existing services around the site or through a new purpose-built utility corridor at the southern most part of the site. This will allow Laing O’Rourke to commence piling work for the new station in 2014.
When completed, the new ticket hall will provide step-free access from street level to the new Crossrail platforms. A subsurface ticket hall will be constructed to link into the existing London Underground one at Liverpool Street.
Well managed site
It was a fascinating, whistle stop tour. At each location, the discipline and attitude to safety was commendable. Every site appeared to be well managed and every manager was clearly aware of the importance of their site in the overall scheme of things.
As the heavy engineering work is completed and Elizabeth and Victoria start to eat up ground west of the station, Laing O’Rourke will slowly take over each site to construct the station fittings and furnishings ready for the opening of the Crossrail service in 2018.
Everything indicates that this will happen according to plan and the end result will be very impressive, even though many people using these facilities will not have a clue about the real engineering work that is taking place today to provide this service tomorrow.
Those working on these sites today will certainly remember and they should feel very proud of what they have achieved.