Tunnel Boring Machines and Tunnelling

Discussion in 'Infrastructure & Stations' started by matacaster, 13 Aug 2015.

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  1. matacaster

    matacaster Member

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    Today I understand the crossrail TBM is being dismantled.

    London is, as far as I am aware mainly clay, whilst the Pennines are a mixture of various types of hard stone.

    I have some questions

    1. Can a TBM be reused on another project - ie what is a TBM's projected lifespan and what governs that lifespan?

    2. Does it need a different cutting head to go through hard stone or does it need recourse to explosives etc?

    3. What speed can a TBM make cutting through London clay and Pennine stone?

    4. What would it cost in general terms to make say a 15 mile tunnel through the pennines and how long would it take?

    5. Can a TBM be sent through an existing tunnel to widen it to say UIC gauge, eg Standedge or if not, is there a more practical solution to tunnel widening?
     
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  3. kjhskj75

    kjhskj75 Member

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    Yes - it's happening at Farnworth.
     
  4. WatcherZero

    WatcherZero Established Member

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    A TBM can be reused but isn't usually as it is designed for the conditions of one particular job and is bulky and difficult to transport even when dissambled, they are often once they complete their assignment directed off route into their own stub tunnel where they can be just abandoned and scavenged. The most expensive part is also the cutting head and that is usually worn out after a job.

    2. Yes needs different shaped heads depending on material its cutting through.

    3. One designed to cut through clay couldn't cut through stone and vice versa.

    4. In the order of £100m per mile is often quoted, time depends on many factors such as the material its going through and how many tunnelling machines you use.

    5. Yes a TBM can be used to widen a tunnel as long as that wider tunnel wont be compromised (e.g. if threaded between underground structures, foundations and cables there may not be room to simply widen it, or it may weaken above surface structures). To keep the tunnel structurally sound and the machine working well you generally fill the tunnel with a material like foam concrete first. It is possible to simple shave a tunnel wider but a lot more time consuming and dangerous, you would normally inject concrete under pressure into the rock surrounding the tunnel to strengthen it.
     
  5. swt_passenger

    swt_passenger Veteran Member

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    A key point about a TBM is that it usually pushes itself forward by bearing on the rings of concrete or steel segments being erected behind it, so will always have a larger diameter than where it has come from. Hence part of the machine often being abandoned below ground as pointed out above..

    However this is usually only the very front part of the overall 'train' of equipment. The majority of the spoil handling machinery and control equipment behind the cutter head can and will be recycled onto another projects.
     
  6. hwl

    hwl Established Member

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    3. Crossrail TBMs target was 100m/week and they were usually faster than that unless they encountered problems. They got serviced including cutting head repairs each time they entered a station box.

    Crossrail had 6 TBMs for Clay and 2 "Slurry" TBMs for the gravel /silt mixture under the Thames on the Abbey Wood Branch.

    I think at least 6 of the machines have already been dismantled with just the last 2 clay machines that were the last to finish being dismantled.

    The Cost of the machines is a very small part of the overall tunnelling cost so any parts being reused go back to the manufacturer for a full overhaul
     
  7. DarloRich

    DarloRich Veteran Member

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    Answer to all yes/ no questions = yes with a but. As for costs, I have no idea!

    TBM, if they are recovered (and not all are) are reused after an overhaul and alterations to fit the requirements of the next project.

    I believe two of the cross rail tbms have been involved in two digs

    One of my engineering heroes is James Henry Greathead upon whose principles the modern TBM is based (Yes i know Barlow and Brunel snr got there first ;) )
     
  8. Philip Phlopp

    Philip Phlopp Established Member

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    I think there's only a couple of other things to add, which has been hinted at above, is that depending on geology, water table height/pressure and unknown springs, topography etc, your mileage really will vary.

    Local geology will dictate not just the cutting head but may also complicate how you approach a tunnelling operation. It may be necessary, where you have to very different types of geology, to have two different TBM setups and meet at the intersection of the two different geologies.

    Local ground conditions will dictate what measures you need to take to prevent the tunnel from collapsing as soon as it's bored, such as earth pressure balancing or a pressurised slurry cutting head system, and that results in machines which have very different equipment design, and which are restricted to the ground conditions for which they are best suited.

    Fillie, the Farnworth Tunnel (re)boring machine is, in blunt terms, an old fashioned system that Marc Brunel would have found very familiar, it's more properly considered a tunnelling shield with power excavation tools and spoil removal equipment fitted, it doesn't have a rotating cutting head that those familiar with CrossRail or the Channel Tunnel would be familiar with. It uses telescopic cutting booms, a mechanised version of a dozen men with pick axes and shovels, essentially.

    The widely shared article from Rail Engineer has an excellent diagram of the machine and an explanation of the machine itself. http://www.railengineer.uk/2015/05/11/boring-boring-boring/

    The good thing about Fillie being old school is that it's not overly specialised for the ground conditions - there are some ground conditions it won't be able to deal with, but when it's recovered and has a service, it will be ready and available for other tunnel re-boring schemes throughout the country, which you will see an increasing number in future control periods as the oldest tunnels become life expired, just like Farnworth was.

    It might just be one of the best investments Network Rail has made in recent years.
     
  9. quantinghome

    quantinghome Member

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    As well as the Farnworth approach (fill with concrete and re-bore), there have been examples of using an annulus-shaped tunnel shield to increase the diameter of a tunnel whilst maintaining services through the tunnel. This was done in the mid-nineties on the Northern Line near Old Street where the old linings needed to be replaced due to acid corrosion from the ground. Trains operated during the day, and the work was done at night, advancing 1-2 rings per shift, so very slow. It is mentioned within this article by London Reconnections:

    http://www.londonreconnections.com/2013/acid-works/

    It was also done as part of the work to develop the Northern Line from various older underground lines in the 1920s, although it must be said it wasn't... ah... entirely successful:

    http://www.railwaysarchive.co.uk/eventsummary.php?eventID=347
    http://www.railwaysarchive.co.uk/documents/MoT_Borough1923.pdf

    However, it would be virtually impossible for this approach to work at Standedge as the existing tunnel is a traditional brick-lined construction, and non-circular, so you couldn't realistically demolish and reconstruct within a night shift.
     
    Last edited: 13 Aug 2015
  10. DelW

    DelW Member

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    TBMs are usually used only in (relatively) soft ground, where they are required to support the face and the short length of tunnel excavated ahead of the primary lining (rings, sprayed concrete, or similar).

    In rock there may be no need for a TBM at all in geology where the rock is self supporting. There are plenty of canal tunnels which are unlined, at least in part, and are still open after 200 years or more.
     
  11. snowball

    snowball Established Member

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    The Penmanbach and Pen-y-Clip tunnels built in the 1980s and 1990s for the westbound A55 in North Wales were built without a TBM. Drill and blast was used in the hard rock sections and made excellent progress. Manual tunnelling with a low-tech shield was used in the soft ground areas and was slower.
     
  12. MarkyT

    MarkyT Established Member

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    I've watched some documentaries (extreme engineering, megastructures, that sort of thing!) about the Gotthard base tunnel in the Alps. They definitely used rotating cutter TBMs through solid granite 3km below the highest peaks and were achieving around 90m a day. Whilst most of the tunnel was being constructed using that technique, a comparatively short section had to be drilled and blasted at a much slower rate of progress after they encountered less stable, more fractured rock that could have collapsed around and damaged the TBM. One of their machines got stuck for a while after a collapse.
     
  13. cjmillsnun

    cjmillsnun Established Member

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    If we're talking about road tunnels (which I don't feel is OT as the technology and engineering applies to railway tunnels), the Hindhead A3 tunnels (one per carriageway) built between 2007 and 2011 were also built without a TBM, but unlike Penmanbach and Pen-y-Clip, they were built using mechanical diggers.
     
  14. DarloRich

    DarloRich Veteran Member

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    Further details on Crossrail TBM dismantling & pictures from Global Rail News:

    http://www.globalrailnews.com/2015/08/12/gallery-dismantling-crossrails-tunnel-boring-machines/
     
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