Crossrail this week said it had decided to significantly resequence tunnelling work in the project’s western section to save money but delay completion.
More from: Crossrail boss sets out tunnelling decision
Combining the contracts means the work can be resequenced for boring the tunnels and platform level station works.
The winning western tunnels joint venture of Bam Nuttall, Ferrovial and Kier (BFK) proposed the move in its joint bid for the tunnels and works for two stations.
The contractor will flip the phases of key works, allowing the tunnelling to be completed ahead of the start of sprayed concrete lining (SCL) work on the platform tunnels.
Crossrail programme director Andy Mitchell explained that the initial plan devised by its consultants assumed that station tunnels would be excavated from ground level ahead of the tunnel boring machines (TBMs) excavating the running tunnels.
Mitchell said Crossrail had encouraged submissions of bundled tenders for the tunnelling along with platform level station works and access shaft contracts.
Mitchell confirmed that all contractors priced up bundled tenders but BFK’s rephased offering for the western section contracts turned out to be cheaper for those packages.
As a result of the proposals, BFK will now drive the 6.16km tunnel from Royal Oak to Farringdon.
After the TBMs have passed through Bond Street and Tottenham Court Road stations work will begin to excavate out from the running tunnels to create the larger areas for the platform tunnels.
“Lorry movements reduced”
Mitchell said the resequencing approach had the added advantage of enabling more of the spoil to be removed through the bored tunnels, cutting lorry movements within central London. But he stressed that this will only raise the volume of spoil removed by rail and barge from 84% to around 89%.
Because the revised approach carries less construction risk, it has allowed Crossrail to reduce the project’s contingency fund. This has brought down the overall cost of the project, although the construction programme will be longer. As a result, the central section is now due to open in 2018, not 2017 as originally planned.
Adopting this new plan also forced Crossrail to reissue the tender for Farringdon station where the western and eastern tunnelling contracts meet (NCE 2 December). Contractors building Farringdon station may not be needed to create 400m long pilot tunnels as part of the station construction contract.
Mitchell said the original plan of creating the platform tunnels and some of the access shafts before the TBMs pass through would remain in place on the eastern section.
Primarily, this was because none of the bidders on this section proposed such an approach, said Mitchell.
The eastern section is much longer than the western section at 11.95km. Waiting for TBMs to pass through Whitechapel and Liverpool Street stations before starting work on the SCL platform tunnels would risk delaying the project.
The £500M eastern tunnelling contract was awarded to a Dragados/John Sisk joint venture.
SCL excavation and early access shaft work for this section has been let separately to Balfour Beatty, Morgan Sindall, Alpine BeMo and Vinci Grands Projets.
Mitchell confirmed to NCE that the remaining tunnelling contracts – for the tricky refurbishment of the 550m long Connaught Tunnel and driving the 2.64km long Thames Tunnel between Plumstead and Woolwich – will be let in the next couple of months.
Crossrail is now in talks with developer Berkeley Homes to resolve issues concerning its promised funding for the station box at Woolwich station. Berkeley had been reluctant to commit to this during the economic downturn. Major station contracts will be awarded from late summer 2011, Mitchell added.
Merged contracts to save Crossrail money