CivilNotePpt

Safety Precautions in Tunnelling

Maintenance of Railway Tunnels

18 Safety Precautions in Tunnelling

Tunnelling is an underground construction and there are many types of risks during construction. Therefore, it is essential to take measures to protect the workers from accidents. Following are the 18 Safety Precautions in Tunnelling.

1. The floor of the tunnel should be kept dry and clean.
2. Open flames, electric short-circuiting should be avoided by providing proper covering over the power line and light.

3. Medical equipment and doctors should always be available at the site.

4. Fire fighting equipment with an excellent operator and sufficient water supply should be available at the site at all times.

5. Light and electric lines need to be entirely secured and insulated.

6. Unnecessary machines, tools, and construction material should be avoided to store in the tunnel.
7. All the machines and tools should be maintained in usable condition.

Read Also: Basic Construction Tools List

8. Working platforms should be checked periodically.

9. The communication system (like; a telephone) should be installed inside the tunnels for receiving and sending important information about tunnel conditions.

10. All the internal systems like communication systems, power systems, safety devices, and lighting should be checked periodically.

11. The double power supply should be provided so that the power from the standby unit can be restored during the power failure of one power supply.

12. Removal of rock protrusions by immediate hammering in the wake of blasting is known as scaling. The hammer stroke sound must be hard, not hollow. The hollow sound means loose rock.

13. Every worker must be aware of their safety.

14. Protective clothing, steel helmet, rubber gloves, goggles, etc. should be put on by every worker during their work.

15. The proper ventilation system should be provided in the tunnel as required.

16. Proper drainage must be provided.

17. Safety signboards should be provided at various places along the tunnel.

18. Without permission, no unauthorized person should be permitted to enter the tunnel.

Read More:

Classification of tunnel Drainage System

Maintenance of Railway Tunnels

Generally, P.W.I. inspects every tunnel in his section, and he is personally responsible for maintaining the track through tunnel in perfect running condition. The following points should be noted in connection with the maintenance of railway tunnels.

1. It should be noticed whether the structure of the tunnel has weakened, cracked or deteriorated.

2. Any type of movement of the masonry parts should be noticed.

3. Under the safety of engineering signals, the maintenance of tunnels should be carried out.

4. The track through the tunnel should be in line and level.

5. The P.W.I is liable for the safety of trains and the protection of men who are employed for the maintenance of railway tunnels.

6. The dimensions of the tunnel section should conform to the original dimension.

7. The tunnel tracks’ renewal work should be performed with the utmost priority.

8. The side drains of the tunnel should be cleaned periodically.

9. Light and power lines should be checked to ensure they are properly insulated.

10. It should assure that the tunnel ventilation system is working properly.

11. All weep holes should be cleaned properly.

12. The ventilation shaft should be kept free from growth of vegetation.

13. The precautions to prevent any leakage through masonry joints should be taken.

14. The position of level pillars should be monitored periodically.

15. To avoid the effect of corrosion of rails and sleepers should be examined periodically.

16. The lining of the tunnel should be examined.

17. It should be concerned that unwanted machines, tools, and construction materials are not stored in the tunnel.

Different Shapes of Tunnels

Safety Precaution in Tunnelling

Classification of Tunnel Drainage System

Tunnel Drainage systems are classified as:

(1) Drainage system provided at the time of construction or temporary drainage system.
(2) Drainage system provided in completed tunnels or permanent drainage system.

Classification of Tunnel Drainage System

(1) Temporary Drainage System

This is provided to remove groundwater from the tunnel at the time of construction. In this system, water is removed either by (i) Open-ditch drainage system or (ii) Pumping system.

a) Open Ditch Drainage System:

In this system, water is collected and removed in open ditches, laid with proper slopes at some distance away from the place of work. The open drains or ditches are constructed along the tunnel on both sides at the invert. This drainage system is suitable for rock bases and water-resistant soil.

b) Pumping System:

In this system, sumps are constructed at regular intervals of around 300 m to 500 m. The water is collected in the sumps and is pumped out. For pumping the water, any types of centrifugal pump could be used.

(2) Permanent Drainage System

Permanent Drainage System is provided in one of the following methods:

a) By providing a central Drain

In this system, a central drain is provided between two railway tracks or under the road pavement. It should have sufficient capacity to control the expected water in the tunnel. It should be provided with facilities for inspection and clearing. Inspection manholes should be provided at a distance of 30 m to 50 m.

b) By providing Side Drains

This system is effective for single lane road or railway tunnel where the volume of water to be drained is small. In this system, drains are constructed on either side of the railway track or on the road.

c) By providing corrugated iron shed and side drains

This is provided in tunnels in which water leaks from the roof and side walls of tunnels. By providing corrugated iron shed, shaped to the contour of the roof, water is prevented from dropping on the pavement or railway track. The corrugated shed guides the water to the side drains and is drained out.

Read More:

Methods of Ventilation in Tunnels – CivilNotePpt

Methods of Ventilation in Tunnels

The following methods are implemented for ventilation in tunnels:

Natural Method
Mechanical Method

1. Natural Ventilation

When a tunnel receives fresh air and automatically removes the dust without the use of mechanical appliances, this sort of ventilation is called natural ventilation. This type of ventilation can be improved by providing shafts at regular intervals along the length of the tunnel during its construction.

2. Mechanical Ventilation

When the ventilation in tunnels is done with the help of mechanical devices is known as mechanical ventilation. Mechanical ventilation is done by any one of the following methods:

(i) Blowing

This type of ventilation method is suitable for short-length tunnels. In this system of ventilation, Fresh air is blown by a blower installed in the input shaft. Blowers provide a uniform distribution of fresh air at the workplace, and the vitiated air is pushed out through the portals.

(ii) Exhausting

In this method of ventilation, vitiated air is sucked from the tunnel by using exhaust fans, and fresh air is drawn into the tunnel through the inlet shaft. This method rapidly removes dust and foul air from the working face of the tunnel but does not provide proper ventilation.

(iii) Combination of Blowing and exhausting

A combination of blower and exhaust fan is the most reliable ventilation system. This combined system utilizes the advantages of both blowing and exhausting. Immediately after blasting, the exhaust system is operated for 10 to 25 min to drop smoke and dust, and then the fan is reversed for blowing fresh air.

Factors

The method of ventilation depends on the following factors:

Length of tunnels
Size of Tunnels.
Frequency of blasting and the amount of explosive.
Amount of the heat that is produced by humans, animals, and light.
Amount of carbon dioxide present in the atmosphere due to human breathing and explosives.
The temperature inside the tunnels.
Percentage of humidity present inside the tunnels.

Requirements of Good Ventilation System in Tunnels

A good tunnel ventilation system should meet the following requirements:

1. It should reduce the dust produced by the tunnel activities to a safe limit.

2. It should quickly clear the fumes generated by blasting from the working face.

3. A good ventilation system should be such that, it can prevent the accumulation of dangerous fumes along the length of the tunnel.

4. It should give a working environment at the face of the tunnel.

Read Also:

Classification of Tunnels

7 Shapes of Tunnels – Advantages & Disadvantages

Shapes of Tunnels

Commonly used tunnel shapes(Shapes of Tunnels) are discussed below:

Polycentric
Circular
Rectangular
Egg-shaped
Horseshoe type
Elliptical
Segmental

Shapes of Tunnels - Advantages & Disadvantages

1. Polycentric Shaped of Tunnels

This sort of tunnel shape has a number of centers and provides a sufficient flat base for traffic movement.

Advantages:

It can be used for road and railway traffic.
It can resist external and internal pressure for their arch shape.

Disadvantages:

The construction of these tunnels is difficult.
The lining of this type of tunnel is difficult.

2. Circular Shaped Tunnels

Circular tunnels are used to carry water under pressure. These are not appropriate for traffic tunnels because more filling is needed to make the base flat.

Advantages:

Best to resist the external or internal force.
It provides the greatest cross-sectional area for the least perimeter.

Disadvantages:

More filling is required to form a flat base for designing a road or railway track.
In circular tunnels, lining work is very difficult.

3. Rectangular Shaped Tunnels

For pedestrian traffic, rectangular shapes of tunnels are appropriate. These tunnels are sometimes accepted if pre-constructed R.C.C caissons are used. These types of tunnels are not suitable to resist external pressure due to their rectangular shape and these are not in use these days.

4. Egg-Shaped Tunnels

This tunnel shape has a number of centers and radius length. These are suitable as sewer tunnels to carry sewage water.

Advantages:

It is mostly adopted for carrying sewage water.
Due to their small cross-section at the bottom, it can maintain the self-cleaning velocity of flow of sewage in dry and rainy seasons.
It can resist external and internal pressure due to its circular walls.

Disadvantages:

This type of tunnel is not suitable for traffic tunnels.
The construction process of these types of tunnels are very difficult.

5. Horseshoe Shaped Tunnels

A horseshoe-shaped tunnel is a combined shape of arches and circular tunnel. These types of tunnel shapes are quite popular.

6. Elliptical Shaped Tunnels

For carrying water, elliptical-shaped tunnels are appropriate. These are suitable for softer materials. For better resistance to external pressure, the major axis of these tunnels is maintained vertically.

7. Segmental

Segmental tunnels are suitable for traffic tunnels. It is a section with an arched roof and straight sides. These are generally used for subway or navigation tunnels.

Advantages:

It is the most suited in rock tunnels.
It is suitable to resist external load due to its arch-shaped roof.
It has a flat floor which is helpful for driving and moving any equipment.

Read Also:

20 Types of Classification of Tunnels

Tunnels are generally classified on the basis of their purposes, types of material, and according to their position:

A. Classification Based on The Purpose

Based on purpose tunnels are classified as:

a. Traffic Tunnels

Traffic tunnels are of the following types:

Highway tunnels
Railway tunnels
Navigation Tunnels
Pedestrian tunnels
Subway tunnels

b. Conveyance Tunnels

Conveyance tunnels are of the following types:

Water supply tunnels
Hydroelectric power tunnels
Sewer tunnels
Tunnels for intake and conduit of public utilities
Transporting tunnels in industrial plant

B. Classification Based on Type of Material

Based on the type of material through which they pass, tunnels are classified as:

Tunnels in hard rock
Tunnels in soft rock
Tunnels in loose sand
Tunnels in quicksand
Open-cut tunnels
Tunnels in the river bed

C. Classification based on position or alignment

Based on position or alignment, tunnels are classified as:

Spiral tunnels
Saddle and base tunnels
Off-spur tunnels
Slope tunnels

Read Also:

Requirements of Good Ventilation System in Tunnels

8 Necessity of Tunnels

Necessity of Tunnels

The necessity of tunnels are as follows:

1. Tunnels are necessary, to avoid the long road and railway track construction along the surface of the hill to reach out the other side of the hill.

2. Tunnels are constructed for connecting the two terminal stations, which separated by a mountain.

3. To avoid more depth of open-cut to reach the other side of a mountain. It will be hard to build and maintain if the required depth of the open-cut exceeds 20 m.

4. To protect the road or railway from blockage at high altitudes due to landslides or snowfall.

5. To provide traffic safety from the climatic disaster at high altitude.

6. To save time, so they can use that time for another purpose.

7. To provide a fast and continuous transportation system in large towns, and to avoid holding traffic for a long time due to traffic congestion.

8. To avoid the use of valuable land and property for a road or railway project.

Read Also:

Method of Ventilation in Tunnels