Tunnel drainage systems are classified as temporary systems used during construction like open ditch drainage or pumping systems, and permanent systems like a central drain or side drains. Tunnel ventilation can be done naturally with shafts or mechanically using blowing fans, exhaust fans, or a combination to control air quality, smoke in fires, and temperatures. The type of ventilation system depends on factors like tunnel length and size, amount of blasting, heat sources, carbon dioxide levels, temperatures, and humidity.

1. Unit No. 3
Tunneling
Modern developments in tunnel drainage &
ventilation
Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon-423603
(An Autonomous Institute affiliated to sppu, pune)
Department of Structural Engineering
PROF. S. M. Gunjal
ASSISTANT PROFESSOR, STRUCTURAL ENGINEERING DEPARTMENT

2. Tunnel Drainage
• Good drainage of the tunnels is very essential in order for them to operate safely and
smoothly during the construction period as well as afterwards. The sources of water for
this purpose include ground water and water collected from the washing of bore holes
• Road tunnels are equipped with a drainage system to deal with surface water from
portals, groundwater infiltration through the lining, wall washing water, spillages from a
road tanker and fire fighting water. Some authorities specify the use of slot gutters in order
to maximize drainage performance.

3. 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.
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.

4. 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.

5. 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.

6. Methods of Ventilation in Tunnels
Tunnel ventilation is critical for a variety of reasons. Typically, ventilation ensures an
adequate air quality, controls the spread of smoke in case of fire, and reduces air
temperatures to acceptable limits. ... Cable tunnels require cooling, smoke control and a
certain amount of air exchange.
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 shaft in regular interval along the length of the
tunnel during its construction.

7. 2. Mechanical Ventilation
• When the ventilation in tunnels done by 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 tunnel. In this system of
ventilation, Fresh air is blown by 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 inlet shaft. This method rapidly removes dust
and foul air from the working face of the tunnel but does not provide proper ventilation.

8. 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
fan are reversed for blowing fresh air.

9. Factors and necessity of tunnel ventilation
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 which are produces by human, 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.