Re: Six lane underground rail lines

From: habshi (habshi_at_anony.com)
Date: 01/02/05 

Date: Sun, 02 Jan 2005 21:39:08 GMT

There have been major advances in tunnel-boring machines (TBMs),
invented by the British engineer Marc Brunel in the 19th century. The
past 20 years have seen TBMs built much tougher, more reliable, and to
ever larger diameters. The availability of large TBMs is especially
important for highways because they are the largest tunnels in cross
section. Until the 1960s the largest TBMs were about 8m (25 foot)
diameter, hence most tunnels so built only had space for two lanes of
traffic. Thanks mainly to Japanese innovation, TBMs are now common at
10m (and even go to 14m as in the case of equipment used on the
Trans-Tokyo Bay tunnel) providing room for three lanes of full-sized
truck traffic. Once the principal challenge in tunneling was breaking
up the hard rock and getting the debris out. Now with "road header"
machines, relatively simple machines that deploy a large grinder on an
arm and a conveyor belt, and with simple mechanical excavators and
precise explosives that move the toughest rock, expensive TBMs and
large shields can sometimes be dispensed with.

Another major advance in tunneling is the invention of the jet fan for
ventilation. So named because they look like the jet engine of an
aircraft, they are hung from the ceiling at intervals along the tunnel
and simply move the dirty air along the tunnel. It can be vented out
one end, taken to vertical exhaust risers, or diverted into treatment
channels and reinserted cleaned into the tunnel. On all but the very
longest tunnels, jet fans allow the tunnel builders to dispense with
the plenum or separate longitudinal ducting above a false ceiling that
has traditionally been used to ventilate tunnels. That can reduce the
quantity of excavation and construction by 10 to 20 percent, and
capital costs by comparable amounts. Pioneered in Europe and Japan,
jet-fan ventilated tunnels were long resisted by the U.S. Federal
Highway Administration on the argument that fire might disable the
jet-fans. A breakthrough came in 1996 when live fire tests in an
abandoned tunnel in West Virginia proved their safety, and they were
belatedly allowed in the last designed section of the Central Artery
project in Boston.
 

Q13. What soil types are drilled?
The subsoil excavated from both A86 West tunnels is typical of the
Paris Basin. It includes:

- “Fontainebleau” sands
- High-grade clays (oyster marl, green clay and supra-gypsum marl)
- Limestone and calcareous marl (Champigny and Saint Ouen limestone,
marl, broken stone, rough limestone)
- Low-grade clays (false clays and plastic clays)
- ChalkQ18. How will the A86 West affect surface level traffic?
The decision to link up the A86 West by tunnel will mean shorter
journey times across the western Paris area, and a 15% reduction in
surface level traffic on parallel roads.
(back to top)
Q1. What is the history of the A86 West link-up?
At an average distance of 6km from the Paris city ring road, the A86
constitutes a second Ile-de-France circumferential. It is intended to
reduce traffic on local roads, relieve congestion on the city ring
road, and facilitate travel between suburbs.

The A86 West is the missing link needed to complete this 78km-long
outer ring road, 80% of which is already in service