Tunnelling is a difficult, hazardous, and time-consuming process and the whole operation has to be done systematically so that safety is ensured at all times. Normally accidents in a tunnel occur under the following circumstances.
(a) Falling rocks
(b) During the loading and hauling of muck
(c) Poor handling of explosives
(d) During shaft operations
(e) Cramped working space
The following tips are suggested for preventing accidents during tunnelling operations.
(a) Equipment and tools should be in good working condition.
(b) Regular and detailed inspections should be carried out during tunnelling operations.
(c) Visual inspections should be done to detect seams and planes of weakness so as to avoid the falling of rocks.
(d) There should be provision of sufficient support by ensuring that tunnelling is done properly in order to avoid the collapsing of the tunnel as well as falling rocks.
(e) There should be provision of good lighting and non-slippery walkways, which partially help in relieving the strain of a cramped working space.
(f) Provisions should be made for the removal of extra debris and refuge as well as for good drainage in order to avoid accidents. Efforts should also be made to provide good ventilation.
(g) Telephone facilities should be provided, particularly inside the shaft and at other places in the tunnel, to ensure smooth and accident-free operations.
(h) Firefighting equipment should be provided at all key points.
(i) Safety sign boards should be provided at all key locations.
(j) All workers should be medically fit to work inside the tunnel and they should be examined periodically. Doctors and first aid facilities should be available at the site.
(k) Wearing of helmets by all workers employed in a tunnel should be made mandatory.
Tunnels are required in special circumstances as in when the track cannot be laid on natural ground or when it is not economical. The construction of a tunnel is very tedious and specialized work and, therefore, a very judicious decision is required when it comes to tunnel selection. The method and equipment required to construct a tunnel would depend on the nature of the soil. The tunnel should be provided with adequate light, ventilation, and other safety features.
1. Discuss the points to be considered when determining the shape and size of tunnels.
2. Why are railway tunnels necessary? Draw a sketch to illustrate a single-track railway tunnel.
3. Briefly describe the construction cycle for tunnelling. How are drainage and ventilation facilities provided in railway tunnels?
4. Why is a tunnel necessary? Describe the advantages and disadvantages of constructing a tunnel.
5. Name the various methods of tunnelling in hard and soft rocks. Describe one in each case.
6. What do you understand by shield tunnelling? Discuss the various methods of shield tunnelling adopted in different types of soils.
7. What is the importance of ventilation during tunnelling? Describe the various methods of providing ventilation in a tunnel.
8. Write notes on
(a) Lighting of tunnels
(b) Drainage of tunnels
(c) Lining of tunnels
(d) Compressed air tunnelling
9. Why is it necessary to maintain a tunnel? Describe the various inspections carried out to ensure that tunnels are properly maintained.
10. Describe the various points to be kept in mind to ensure the safety of tunnels. What are the causes behind accidents in tunnels?
11. Differentiate between the following.
(a) Full face method and drift method of tunnelling
(b) Heading and bench method and plot tunnel method