Railway Tunnelling
Introduction
A tunnel can be defined as an
underground passage for the transport of passengers, goods, water, sewage, oil,
gas, etc. The construction of a tunnel is normally carried out without causing
much disturbance to the ground surface.
The history of tunnels is very
old. The first tunnel was constructed about 4000 years ago in Babylon to
connect two buildings. The first railway tunnel in the world was constructed at
the end of the nineteenth century to connect Switzerland and Italy. The cross
section of the tunnel was in the shape of a horseshoe and its length was about
20 km. On Indian Railways, the first tunnel was constructed near Thane on
Central Railways known as the Parsik tunnel. It is the longest railway
tunnel of India with a length of about 1317 m.
Necessity/Advantages of a Tunnel
The necessity of constructing a
tunnel may arise because of one of the following considerations.
(a) A tunnel
may be required to eliminate the need for a long and circuitous route for
reaching the other side of a hill, as it would considerably reduce the length
of the railway line and may also prove to be economical.
(b) It may be
economical to provide a tunnel instead of a cutting, particularly in a rocky
terrain. Depending upon various factors, a rough calculation would indicate
that for a small stretch of land the cost of constructing a tunnel is equal to
the cost of a cutting in a rocky terrain.
(c) In hills
with soft rocks, a tunnel is cheaper than a cutting.
(d) In
metropolitan towns and other large cities, tunnels are constructed to
accomodate underground railway systems in order to provide a rapid and
unobstructed means of transport.
(e) A tunnel
constructed under a river bed may sometimes prove to be more economical and
convenient than a bridge.
(f) In the
case of aerial warfare transportation through tunnels provides better safety
and security to rail users compared to a bridge or deep cutting.
(g) The
maintenance cost of a tunnel is considerably lower than that of a bridge or
deep cutting.
However, the construction of
tunnels is also disadvantageous in certain ways, as enumerated here.
(a) The
construction of a tunnel is costly as it requires special construction
machinery and equipment.
(b) The
construction of a tunnel involves the use of sophisticated technology and
requires experienced and skilled staff.
(c) It is a
time-consuming process.
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