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Contractors battle to extract TBM after silt breaches tunnel

Contractor Kier, along with joint venture partners J Murphy and Interserve, was this week grappling with problems that have halted tunnelling on a £114M project for United Utilities.

NCE can reveal that silt has breached the tunnel lining along the 3.5km long, 2.85m diameter storm water tunnel underneath Preston and Penwortham in Lancashire being formed by a tunnel boring machine.

As a result, work on that section was stopped on 24 November and the TBM has not progressed since.

The revelation is likely to cause most embarrassment for Kier, which just before Christmas became one of the biggest winners in the Crossrail award of tunnelling contracts (NCE 16 December 2010).

In joint venture with Bam Nuttall it won a £500M contract to build the west running tunnels and Bond Street and Tottenham Court Road sprayed concrete lined tunnels.

It could also cause problems for J Murphy and Sons, which in September, in partnership with Hochtief, was shortlisted for the complex Connaught tunnel refurbishment for Crossrail.

GHA Livigunn produced the detailed design for the scheme, using Donaldson Associates as specialist sub-consultant for the shafts and tunnels.

The joint venture, KMI Water, is using a Lovat earth pressure balance TBM, which engineers now must work out the best way to recover.

“Investigation work is taking place to determine what steps are required to rectify the situation,” said a United Utilities spokesman.

“We are now working through an engineering solution to commence tunnelling again.”

The contractors said they were unable to comment on the cause of the breach.

“We are now working through an engineering solution to commence tunnelling again.”

United Utilities spokesman

Engineers told NCE that the first thing to look at was ways to get rid of the spoil that has been produced by the TBM. Once this is completed there are three main ways to retrieve the TBM, they said.

One option involves digging a shaft to remove the TBM. This is dependent on the ground conditions above the machine, however, it is possible because the area above the machine is understood to be greenfield.

Another involves freezing the ground surrounding the TBM.

The final option is to grout the surrounding ground to stabilise it and allow the TBM to be withdrawn.

Engineers would pump a cementious grout in the void in between the tunnel lining and the TBM head, which alleviates pressure on the TBM to enable its removal

Readers' comments (3)

  • Barry Walton

    Sirs,

    Apparently, the contractors have struck very difficult ground conditions in the tunnel in Lancashire. That may prove to create a critical delay in terms of the construction contract, be challenging to resolve and, as it may overlap with other similar or other demanding works, have knock on tehnical and financial effects. Once solved it will be a blink in the eye of the working life of the tunnel and an additional cachet of knowledge in dealing with underground conditions. It is not, obviously, a cause for embarrassment and NCE would do itself (or at least the memership) no harm to stay clear of such unhelpful side sauces to interesting engineering problms.
    B Walton (F)

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  • This is a bit of a missed opportunity NCE, surely a better story would have been focussing on how the Engineers intend to rectify the situation, what challenges and uncertainties they face and even how their expertise will aid them in meeting this onerous obligation. Clearly rising to this sort of challenge is what Civil Engineers are expected to be good at.

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  • Michael Paul

    In my experience very few major tunnellling projects go completely according to plan, without any problems. I therefore also don't see why the contractors should be "embarassed" or any immediate connection with other projects. A bit more engineering information, such as the prevailing ground conditions, the extent of the problem zone etc. would have been more interesting, and more fitting for NCE. I wish those involved every success in their search for a suitable solution, and, having been involved with a similar problem some years ago in the Siegburg tunnel on the Frankfurt-Cologne rail link, look forward to a detailed report.
    Mike Paul

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