Contractors must build 25.6km of tunnels through soil strata that varies from London clay to Woolwich and Reading sand beds to the east, avoiding existing services, Tube tunnels, underground rivers and building foundations that congest London's subterranea. At points the tunnel will be almost 40m below ground. The deepest station, Liverpool Street will be some 30m under the surface.
The route alignment, safeguarded 12 years ago, has been determined by the extensive underground infrastructure and location of existing deep building foundations.
Substantial pre-planning and design work has been carried out to demonstrate that the scheme is technically feasible. Listed buildings along the route have been assessed and vulnerable structures highlighted for strengthening. Tunnel boring operations will incorporate the latest elements of proven best practice in order to minimise groundborne noise and vibration.
A staggering estimated 8Mm3 of waste is to be generated by this project. Most of the spoil removed from the twin 6m diameter tunnels will be removed from four portal sites, keeping local disruption to a minimum. Around 15% of surplus materials will be moved by barge, 30% by rail and 55% by road.
A new temporary service deck will be constructed on the site of 4Đ18 Bishop's Bridge Road. The new structure is expected to take eight months to build. During the five-year Crossrail programme at Paddington, it will accommodate station deliveries, British Transport Police parking and custody transfer bays, and a refuse disposal skip and compactor.
For the main tunnelling works at Paddington location, bentonite silos (for diaphragm wall construction of the station box) will be situated at the southern end of the worksite.
Tottenham Court Road
The Astoria Theatre on Charing Cross Road will be demolished to accommodate the main works associated with the construction of Tottenham Court Road station plaza (eastern) ticket hall.
Traffic management will be the crucial issue during the construction of this station.
Six stages of traffic management have been proposed and with each there will be significant changes to road layout, traffic flows, bus routes and pedestrian walkways following a rolling programme.
Construction of a Farringdon station is expected to take around five years with works taking place on five separate sites: Cardinal House, Smithfield Market, Lindsey Street, Fox and Knot Street and Farringdon crossover. Two new ticket halls will be constructed: a western facility on the south east corner of Farringdon Road and Cowcross Street and an eastern equivalent at Lindsey Street.
The station will consist of two platforms fitted out to 210m although the tunnel will be constructed to facilitate extensions to 245m should the need to operate longer trains arise. Vehicular access is expected to be the main bone of contention during construction of this station.
The new station, which will serve the City and provide interchange with LUL and National Rail services at Liverpool Street and Moorgate stations, will be located between Liverpool Street and Moorgate.
Moor House, built four years ago, houses the ticket hall for Moorgate station which will be adopted for Crossrail. The Moor House development also contains a 40m-deep draught relief shaft, which was built in its lower basement expressly for the Crossrail development.
A significant aspect of the enabling work at this station will comprise of diverting the North Eastern Storm Relief Sewer, the relocation of an electricity substation (and associated cabling) and the temporary pumped diversion of a small diameter sewer severed by the Essex Wharf box (all within Swanlea School grounds and Essex Wharf).
Isle of Dogs
The station is being built under the West India North Dock. The dock will be dewatered and the possibly contaminated sediment will be removed to allow for station construction.
The dock will be dewatered for three years. This, combined with dewatering for seven other vent shafts, will mean that 30M m3 of ground water will be abstracted from wells, causing significant drawdown of water levels in 25 licensed abstractions.