Mammoth "Metal Moles" Tunnel Deep Beneath London

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."

Comments

Re:GPS?

[garyebickford]

I don't know the specifics of this, but from my former work in an oilfield services company, I know that oil well drilling systems can track their own position within a few inches. One example from about 30 years ago was a set of wells drilled under an estuary in the UK. The gov. allowed the drilling company a one-acre island to do all the drilling from. They drilled down about a mile, then branched off into 10 separate holes that were drilled horizontally, following an oil seam that at times was only one foot high. The longest horizontal hole was about 10 kilometers (34000+feet, 6.6+ miles) long. Here is another reference, including info on a new well system on the North Slope that extends even farther - two miles down, then over 10 km horizontally, then back down another km or two so they can use an existing oil processing facility.

Drilling systems are among the most sophisticated technological marvels going - they include seismic signalling, mass spectrometry, neutron activation analysis, nuclear magnetic resonance, gamma ray spectral analysis, and other really geeky stuff. The bit knows where it is geographically and where it is relative to the geological structures that it is following. The computers that sit 10 feet behind the actual bit meet tougher specs than military or aerospace - 1000 G shock, very high pressures (I forget the PSI), 400 degree F temperatures. Cooling is accomplished by the drilling fluid that is going past the outside of the drill string. Truly oil well technology is the perfect geekly combination of extreme "big heavy dangerous machines" plus extreme high tech.