The start of the High Speed 2 (HS2) construction programme has been pushed back again as contractors struggle to keep the project to its £56bn target build cost.
Last week, HS2 Ltd confirmed that it had put back the notice to proceed (NTP) for the main civil works packages until an undisclosed date “later this year” – with November tipped by many to be the latest date. This is to allow the contractors to cut construction costs further.
The main civils works contracts are divided into two stages, with HS2 Ltd giving the NTP at the end of stage one which focuses on concept/scheme design.
During this phase, contractors work with HS2 Ltd to finalise cost estimates ahead of the award of the NTP which triggers the start of construction.
Yet, while the start of construction has been delayed by a further six months – after already being pushed back from February – the opening date for phase 1 connecting London and Birmingham remains fixed at 2026.
This work involves building 230km of new high-speed line with around 40km of 8.8m diameter twin bore tunnel, ventilation shafts, maintenance depots, numerous viaducts, bridges, cuttings, overhead lines to be installed, commissioned and tested in just six years.
The original HS2 documents set out a construction programme of almost eight years starting in spring, 2018.
But can it still physically be done, and within budget?
Building the tunnels along the line will form one of the major parts of the construction programme.
Using Crossrail as an example, it took three years working 24 hours a day, seven days a week, with eight tunnel boring machines (TBMs) to complete 21km of twin bore tunnels.
The Crossrail TBMs were 6.6m in diameter, and the HS2 ones will be 8.8m in diameter, although one tunnelling expert told New Civil Engineer that the larger diameter would not make a discernible difference in the speed of the machines.
To keep the same pace, which it would need to do to stay on track, HS2 would therefore need something near 16 TBMs.
But this poses its own problems. Given that the HS2 TBMs will most likely be bespoke, at least 18 months would be needed from ordering them to getting them on site.
“HS2 is going to have to be careful,” another tunneller told New Civil Engineer.
“Sixteen TBMs is a large order, which could add a significant amount of time to procure.
“With a minimum of 18 months to get them to site, then say three years to build the tunnels, that’s four and a half years.
“That doesn’t leave the longest time for fit out and testing. You’ve only got to look at Crossrail to see that.”
A separate major project source said the process could be speeded up if HS2 Ltd procured the TBMs now on the contractor’s behalf – something HS2 Ltd has yet to publicly explore.
One thing going for the line is that it will largely be going through greenfield land which will reduce the time needed to build it. But the complex challenge around interfacing with the two southern stations at Euston and Old Oak should not be sniffed at.
And while the construction start date had been pushed back, enabling work is still at over 60 sites, with early works contractors on site at the two most complex stations – Old Oak and Euston.
Like what you’ve read? To receive New Civil Engineer’s daily and weekly newsletters click here.