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How HS2 tunnelling will be impacted by construction delay

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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

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Readers' comments (5)

  • Why is everything "impacted" nowadays? Things used to be "affected". C'est la vie.

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  • David Hall

    Plainly there's some excellent strategic thinking here; the budget is over optimistic, so lets move the start date back a year and keep the finish date the same ?!

    This sound like the opening of another case study into the use of the often-practiced operating model "a wing and a prayer" ... the schedule wing and the budget prayer?

    Clearly tongue-in-cheek .... and lets hope not too close to reality. Like the previous viewpoint, hardly the best way to promote confidence in industry-best practices and customer-success outcomes.

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  • TBH I think the whole project should be scrapped and money spent on further upgrades to existing systems all over the UK, preferably not via Network Rail. Getting rid of first class on intercity trains would probably free up enough space as HS2 will provide!

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  • Do it cheap
    Do it well
    Do it quick

    They say you can do any two of these but never all three. I suggest we dispense with do it quick and concentrate on the other two.

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  • Philip Alexander

    We should dispense with HS2 altogether and save the whole £100+ billion ( less of course the disgraceful £4 billion already spent).
    As Mr Wren points out, spending that sort of money on increasing the capacity on the existing conventional network could transform rail travel in the UK.
    The HS2 heirarchy seem to be wriggling around trying to justify this useless project after accepting that high-speed is not its purpose any more. A bit late to be coming to that conclusion don't you think?
    They've realised what the rest of us thinking engineers knew years ago, that the network proposed is too short for journey time savings to be of any value, especially given that most rail users are able to work on trains these days. So there's no real monetary value (in economic terms) in journey time savings thus destroying any economic justification for the project.
    So they now try to justify it in terms of capacity. Rubbish. You can't mix freight with high speed passenger trains so it relies on finding more train paths on existing lines due to passenger demand transferring to HS2. Again rubbish. Most train journeys in UK are sub 100 miles so what would be the point of spending a huge price premium to save 10 minutes on a journey between two places you don't want to set off from compared with your existing departure points?
    Augmenting the existing network with extra running lines and sorting out pinch points which cause delays would be a far better use of funds and deliver massively better BCR.
    Why can't the politicians understand this? Oh yes, they are all too busy covering themselves with Brexit glory and so far up themselves that they can't afford to spend any critical thinking time on government expenditure on a gigantic scale. If that's not their job, what is?

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