Gently does it' would make a suitable slogan for construction of the northern ticket hall at London's King's Cross St Pancras Underground station.
On the face of it, it's a relatively short tunnelling project, but it really isn't that simple. 'If you talk with someone who's worked on, say, the CTRL tunnels, they'll pooh-pooh this project, ' says Balfour Beatty Management project manager David Darcy.
'We've only got a few hundred metres of tunnel to deliver.
But the ground is incredibly congested. It doesn't allow production tunnelling ? there's nothing you could get a good run at. It's very careful, controlled work.' The new four-level ticket hall is being excavated a few paces from two listed buildings ? the 19th century Great Northern Hotel and the King's Cross station shed itself ? as well as tunnels and escalator bores linking the ticket hall with the Northern and Piccadilly lines.
Network Rail's Thameslink line must also be threaded under the hotel and station, around water mains, sewers and gas pipes, and over, between and under the Tube lines themselves.
London Underground has commissioned the construction of the ticket hall to increase the capacity of the station, which often has to close at peak times because of overcrowding. Work started on site in 2002, but, with piling well advanced, the project stuttered to a halt in 2004 as government funding commitments wavered.
But further pressure on the station from the forthcoming introduction of commuter services on the Channel Tunnel Rail Link (CTRL) into St Pancras station created new impetus for the project. Passenger numbers are expected to rise from 50,000 a day to 90,000 a day when fast commuter services from Kent to St Pancras are introduced alongside Eurostar services in 2010. As a result, the northern ticket hall's costs were reviewed. Construction was finally given the green light again a year ago.
There are distinct halves to the project, which is being run by Balfour Beatty Management.
Balfour Beatty Civil Engineering has almost nished excavating the first level of the three-level ticket hall box, which is being constructed top down under a $227M contract (see box).
The other half involves a joint venture of Morgan Est and Beton & Monierbau, known as Morgan Bemo, constructing tunnel links between the existing Tube ticket hall, the Northern Line, the Piccadilly Line and to Network Rail's Pentonville Road Thameslink station.
Darcy says that the work is being carried out against a challenging programme.
Tunnelling is advancing from a 22m deep shaft in the north-east corner of the ticket hall. 'We have to finish tunnelling from the shaft by March 2008 to enable Balfour Beatty to carry on with its works on the ticket hall. The ticket hall ground level slab has to be handed over to Network Rail on 1 September 2008 so that it can get on with building a western concourse for King's Cross main line station.' The project is due for completion in early 2010, but Darcy is expecting London Underground to ask for completion in late 2009. 'We'll have no problem achieving that providing we are asked soon.
The main challenge will be order times for equipment like escalators and lifts, ' he says.
Client: London Underground/ Metronet Designer: Arup Project management: Balfour Beatty Management Contractor for ticket hall: Balfour Beatty Civil Engineering Contractor for tunnels: Morgan Est/Beton & Monierbau JV Main piling subcontractor: Bachy Soletanche, with plunge columns by Stent and additional piling by Skanska Cementation Foundations Grouting subcontractor: Bachy Monitoring: Sol Data Tunnelling contract value: $118M Ticket hall excavation and fit-out value: $227M