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(
December 2020
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A
tunnel
is an underground passage. Some tunnels are used for
cars
, and others are used for
trains
. Sometimes, a tunnel is used for movement of
ships
. Some tunnels are built for
communication
cables and some are built for
electricity
cables. Other tunnels are built for animals.
[1]
Wikimedia Commons has media related to
tunnels
.
Tunnels are dug in different kinds of
grounds
, from soft
sand
to hard
rock
. The way of digging is chosen by the type of ground. There are two additional ways of digging :
quarry
and 'cut and cover'. In quarry, the tunnel path is drilled in a horizontal way.
This system requires a deep tunnel that's built in a firm rock. In the 'cut and cover' system, a tunnel is dug in the ground and, afterwards, a
roof
is built above the tunnel. This system fits tunnels that are close to the ground like road tunnels and
infrastructure
.
Building tunnels is a large
civil engineering
project that could cost very high sums of money. The planning and building of a long tunnel may take many years.
The
Channel Tunnel
between
France
and
England
is one of the longest tunnels in the world. It is 50 kilometers long. The longest tunnel in the world, the
Gotthard Base Tunnel
, is being dug in
Switzerland
.
- A
subway
is based on a network of tunnels that are dug underground so the trains will not disturb and will not be disturbed by the local transport.
- On the path of a
railroad track
or a
road
a tunnel is dug when the lane encounters an obstacle such as a
mountain
to avoid bypassing the obstacle.
- A tunnel is built sometimes to overcome a
water
obstacle as a replacement for building a
bridge
above it.
- A tunnel is built to connect between
military
posts so the movement between them will not be visible for the enemy.
- A tunnel is built for infrastructure like electricity cables, water, communication and sewerage to avoid damage and disruption above ground.
- Some tunnels are used by
prisoners
to escape
jail
.
- Sometimes tunnels are used by
criminals
to do a bank robbery (e.g. in
Brazil
, Summer 2005).
Cut-and-cover
is a simple way of making hollow tunnels where a
trench
is hollowed out and
roofed
over with an overhead support system strong enough to carry the load of what is to be built above the tunnel.
Two basic forms of cut-and-cover tunneling are available:
- Bottom-up method
: A trench is hollowed out, with ground support when needed, and the tunnel is built in it. In earliest days bricks were used. The trench is then carefully filled and the surface is reinstated.
- Top-down method
: Side support walls and capping beams are made from ground level by such methods as
slurry walling
or neighbouring bored piling. Only a hollowed out excavation is needed to construct the tunnel roof using beams or in situ concrete sitting on the walls. The surface is then remade except for access openings. This allows early recreation of roadways, services, and other surface features. Excavation then takes place under the permanent tunnel roof, and the base slab is made.