Operation Involved in tunneling
The hard rocks tunneling method has following sequence of operation for construction of tunnel :-
- Loading of holes
- secondary blasting
- tunnel supporting
- Grouting and lining
1. Drilling :- Tunneling with explosive requires drilling of holes in to rocks. A drill holes are made with drills worked by compressed air. the depth of the holes varies from 2 to 3 metre.
2. Loading of holes :- Charging the holes with explosives is known as loading of holes. It is the operation performed to loosed the rock, each holes is charged and loaded with explosive.
3. Blasting :- After loading the holes next step is blasting. warning signal are sounded for safety.
4. Scaling :- At the end of Blasting some rock fragments hang loosely from ceiling and walls of tunnels .removing of such loose rock fragments and hammering off projecting rock is known as scaling.
5. Mucking :- It refers to the operation of loading and removing the excaved or blasted material and dumping it at the selected place.
6.Secondary blasting :- Main blasting may not gives desired profile to the tunnel. therefore to achieve proper shape of tunnel the process of secondary blasting is done.
7. Tunnel supporting :- The interior surface of the blasted portion is supported by timbering to avoid accidents immediately after mucking.
8. Grouting and lining :- Before the tunnel is finally lined , it is necessary to grout the weaker section with cement slurry so that the weaker strata is stabilized. finally the tunnel is lined .