Mammoth "Metal Moles" Tunnel Deep Beneath London 294
Posted
by
samzenpus
from the it's-burrow-time dept.
from the it's-burrow-time dept.
Hugh Pickens writes "BBC reports that the first of eight highly specialized Tunnel Boring Machines (TBM), each weighing nearly 1,000 tonnes, is being positioned at Royal Oak in west London where it will begin its slow journey east. It will carve out a new east-west underground link that will eventually run 73 miles from Maidenhead and Heathrow in the west, to Shenfield and Abbey Wood in the east. Described as 'voracious worms nibbling their way under London,' the 150-meter long machines will operate 24 hours a day and move through the earth at a rate of about 100m per week, taking three years to build a network of tunnels beneath the city's streets. Behind a 6.2-meter cutter head is a hydraulic arm. Massive chunks of earth are fed via a narrow-gauge railway along the interior of the machine, which is itself on wheels, as the machines are monitored from a surface control room which tracks their positions using GPS. Hydraulic rams at the front keep them within millimeters of their designated routes. 'It's not so much a machine as a mobile factory,' says Roy Slocombe, adding that the machine is staffed by a 20-strong 'tunnel gang' and comes with its own kitchen and toilet. Meanwhile, critics complain that the project is a peculiarly British example of how not to get big infrastructure schemes off the ground, because almost 30 years will have elapsed from its political conception in 1989 to its current projected completion date of 2018."
Why exaggerate? (Score:4, Insightful)
From the summary:
the 150-meter long machines...
From the article:
The 140 metre long, fully assembled tunnel boring machine...
At 140 metres, each TBM would just fit just inside the boundaries of a cricket oval.
Was 140 meters not impressive enough, so the submitter had to add 10 meters?
Re:GPS? (Score:2, Insightful)
From TFA:
The machines are monitored from a surface control room which tracks their positions using GPS.
So this would be more like having GPS in your dive boat than having GPS underwater.
Nothing 'peculiarly British' about it... (Score:3, Insightful)
There's nothing peculiarly British about partisan politics resulting in funding taking years to be approved and plenty of NIMBYs protesting the plans!
Life doesn't begin at conception (Score:5, Insightful)
You can't count the life of a project from the date someone first thought of it. By that measure, the Apollo moon landing project took at least 100 years. You should start counting from the date significant funding began, which in this case is 2010. Not bad, compared to, say, Boston's Big Dig.
Re:Life doesn't begin at conception (Score:2, Insightful)
30 years only seems like a long time to people in their 20s.
Re:Tunnelling under London... (Score:4, Insightful)
That's sincerely reassuring then, and I thank you. I hadn't thought they could successfully reinforce tunnels a tenth of a kilometer wide.
Um, what?
The tunnel diameter is 6.2 metres, i.e. a bit bigger than the cross section of a train + emergency walkway. The new, underground station platforms will be 250 metres long (wow!) but still only ~18m diameter (my guess from the mock-up video [bbc.co.uk]). Presumably they've planned for enough space for most of the "some 1,500 passengers ... carried in each train at peak periods" to get off at a single station.
Tunnelling can cause problems though. For example, London's local Quake II level [wikipedia.org] (see picture) required some special work to avoid the Houses of Parliament collapsing.
Re:GPS? (Score:5, Insightful)
Sometimes a white trailer is the right tool for the job. I've worked with civil engineers for years, and the ones I've worked with were pretty full-on professional. If a job needs a white trailer, that's what they trot out. If the job needs a million dollar visitor centre, then that goes into the spec.
It's probably worth mentioning that there's GPS, and then there's GPS. The sort that we are used to ("In 400 metres, exit ramp, on left, to Proposed Western Freeway"*) depends entirely on trig between orbiting satellites, another more sophisticated type augments that with intertial guidance systems. If you can read the RF from the satellites, you can use the former - and that depends on a combination of antenna design and how much (generally metal) is in the way that might soak up the radio frequency energy before it gets to the box. To a point, you can make up a lot of signal strength with a higher-spec antenna.
The latter type of (what's erroneously, but conveniently called GPS), the inertial guidance system, measures and sums accelerations and gives you a vector -- sort of like summing the movements of a small mass in an enclosed box over time. These can use accelerometers and gyroscopes to add up quite small movements and tell a computer in summary that it's gone this far, in this direction, over this interval of time. If it sounds complex, you're right -- but the technology has been available since the advent of the ICBM.
The Wikipedia entry on the subject is really quite good -- http://en.wikipedia.org/wiki/Inertial_guidance_system [wikipedia.org] -- worth reading (warning, there is a lure and fascination in these things, especially when you get to laser gyroscopes...)
And as much as I like my little Garman Nuvi (*yes, it really did give me that direction once) it wouldn't be the GPS of choice for locating a major piece of underground tunnelling kit.
Uhm. (Score:4, Insightful)
You have heard of the Channel Tunnel haven't you?
They dug from both ends and met in the middle, under much deeper water than the Thames, and were only a centimetre out.
Re:GPS? (Score:4, Insightful)
Lasers are used underground to determine the location. If there are turns, mirrors are used.