Re: Six lane underground rail lines

From: Androcles (dummy_at_dummy.net)
Date: 01/02/05 

Date: Sun, 02 Jan 2005 21:41:56 GMT

"habshi" <habshi@anony.com> wrote in message
news:41d8692c.14596628@news.clara.net...
> 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

Not exactly granite, then.
Androcles.

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