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ADVANTAGES OF TUNNELLING:
(i) Generally, when the depth of open-cut is more than 18 m, tunnelling is economical.
(ii) Tunnels carry railway lines, roads and public utility service like water, oil, gas, etc. economically. Across stream or mountain.
(iii) Tunnels avoid traffic congestion and provide rapid transportation in crowded cities.
(iv) Tunnels connect two terminal stations by the shortest route.
(v) Milder grades in tunnels reduce handling cost.
(vi) Tunnels protect bombing during aerial warfare.
(vii) Tunnels carry water to generate power.
(viii) Tunnels provide protection against weathering agencies.
(ix) Tunnels avoid acquisition of costly land or property.
DISADVANTAGES OF TUNNELLING:
(i) The initial construction cost of a tunnel is higher when compared to an open cut.
(ii) Tunnel construction requires more time in construction when compared to open
cut.
(iii) Tunnel construction requires specialized matters and sophisticated equipment.
(iv) Tunnel construction requires skilled labour and strictest supervision. The choice between a tunnel and an open cut depends upon local conditions, type of rock and available equipment. Generally, when the open-cut vertical depth exceeds 18 m, it is economical to build a tunnel.
The open cut suffers from the following disadvantages:
1. It requires larger lengths.
2. It requires higher maintenance cost.
3. In case of railway tracks in open cuts, the larger locomotive is required due to stop grades.
4. It is not at all safe during aerial warfare.
5. Highway pavements in open cuts are affected by the adverse action of weathering
agencies.
6. Open cut adjacent to the facility is dangerous.
