8. 8
8
Underground water conduits are
built for water supply and water
power plants. For hydroelectric
purposes the water is conducted
from an elevated reservoir to a
low lying powerhouse.
The conduit is generally
subdivided in a more or less
horizontal headrace tunnel and
an inclined or vertical shaft.
Underground water conduits
Turbo
pumps
11. 11
11
An aerodynamic pressure rise
causes discomfort of the passengers (unless
the cars are pressure-tight), and,
Produces noise near exit, and,
constitutes a load acting upon the lining.
12. 12
12
Comparison
between one-tube with two tracks and twin tubes
Cost
Enveronment
Big
Small
Aerodynamic
Easier in case of fire,
stop operation only in
one tube
Difficult in case of fire,
fully stop operation
Disaster
prevention
and rescue
Helpful from piston wind
No help from piston wind
Ventilation
Bigger section, bigger
deformation, higher risk
Difficulty
and risk
Two-tube with one track
one-tube with two tracks
Comparison
Smaller section, smaller
deformation, lower risk
Small Big
Lower Costs 20-40% more
Tunnel length <10km: one-tube with two tracks
Tunnel length >20km: Two-tube with one track
13. 13
13
Warning：
With respect to double tracks in one tube, one should
take into account that a high speed train should not
encounter a freight (货运) train inside a tunnel, because it
could be endangered by falling items.
Flying block
14. 14
14
Choice of tunnel alignment
1. Depends on geotechnical conditions, traffic, hydrological,
risk management, excavation method (drill & blast or
TBM).
2. To minimize the disturbance of the environment, aspects
of vibration (e.g. due to blasting), noise and ventilation
should be considered.
3. In road tunnels, straight alignments longer than 1,500m
should be avoided, as they could distract the driver.
4. Furthermore, to avoid excessive concentration on one
point, the last few meters of a tunnel should have a
gentle curve in plan view.
15. 15
15
A high level tunnel is much shorter and reduces
geological risk (because of the reduced cover). On the
other hand, the operation is more expensive because
of increased power consumption and increased wear of
the waggons. Velocity is reduced and traffic
interruptions or delays during winter must be factored
in.
A base tunnel is much longer and, therefore, much
more expensive and difficult to construct. But it offers
many operational advantages.
Choice between a high level tunnel and a base tunnel
16. 16
16
Cost of tunneling
The reasons behind the success of Madrid are:
good and extremely lean management (enabling
decisions in 24 hours), own project management
(solution of disputes before they arise), and,
the appropriate selection of construction methods (full
face methods forbidden, open faces no greater than 5
m2, selection of extremely powerful EPB tunnelling
machines).
17. 17
17
Installations in tunnels：
Installation for traffic control
Installation for telecommunication
Ventilation
Fire protection
Illumination of road tunnels
Drainage
18. 18
Costs in tunneling of Plabutsch western tube (road
tunnel, 9.2km long)
%
8.5
70.5
1.8
13.9
4.5
0.8
19. 19
Installation for traffic control
Road signs
Traffic lights
Traffic guide equipment (floor labelling, side reflectors)
Traffic census. Peak of maximum allowable traffic
Height control to catch oversized vehicles before they enter the
tunnel (measured e.g. with photo-sensors)
Video-monitoring of those tunnels longer than 1,500 m or with a
high traffic density.
Modern sensors provide warning of traffic slow down (e.g. due to
a fire).
20. 20
Accidents in tunnels
The frequency of accidents in road tunnels is reduced by
ca 50% compared with open roads. The reasons are:
Speed limits in tunnels are, in general, accepted by
the users.
Snow, ice, wind, rain and fog are rarely encountered
in tunnels.
One should, however, take into account the
consequences of accidents in tunnels which are
much more severe than on open roads.
21. 21
Installations for telecommunication
Equipment for emergency calls: These have to be
provided in tunnels of more than 500 m length with a
spacing of 150 m. Portals and U-turn niches should
also be equipped with emergency call facilities.
Telephone boxes should be provided with glass doors
that can be opened toward the tunnel.
Service telephones: These telephones have to be
provided in tunnels of more than 1000m in length at
every service station and also in every control room.
They are dispensable if radio communication facilities
are provided.
Radio communication: In those tunnels longer than
1000m or with a high traffic density, radio
communication should be provided for fire brigade,
police and road administration as well as for traffic
announcements via radio. Radio re-broadcasting
22. 22
Ventilation
Two different systems of ventilation:
Ventilation during construction (i.e. during the heading
of the tunnel) ;
Service ventilation (i.e. during the operation of the tunnel).
Expenditures on the latter amount occupies up to 30% of
the total construction costs.
23. 23
Ventilation during construction
Supply with oxygen: The O2-content of air should not
fall below 20 vol.%. Below 18 vol.%2 breathing is not
possible and protection masks should be used. The
lack of oxygen is due to:
Combustion motors
Breathing
Oxidation of wood, coal etc.
Ground water dissolves more O2 than N2
Cleaning-up of air: The following pollutants have to be
removed
Dust from rock excavation and shotcreting
Combustion motors
Blasting fumes
Gas egression from rock
Radon decay products.
26. 26
Ventilation during operation (Service ventilation)
Four types of ventilation techniques:
1-Natural longitudinal ventilation: This ventilation is
accomplished by the pressure difference between the
portals and also by the piston action of the vehicles.
2-Fans: These produce a longitudinal ventilation. The
blowing direction is reversible. Large ventilators
achieve a higher thrust related to installation costs.
27. 27
3-Semi-transverse ventilation: Fresh air is supplied from
special pathways perpendicular to the tunnel’s longitudinal
axis, whereas the polluted air escapes from the portals
(supply system). This is appropriate for tunnels with 2 to
4km length and medium traffic load.
Alternatively, the used air is extracted through special
ducts, while fresh air enters through the portals.
28. 28
4-Transverse ventilation: Fresh air is introduced and
polluted air (which moves upwards) is extracted
perpendicular to the tunnel axis.
31. 31
Fire protection
Because of the confined space, fires in tunnels can be
disastrous.17,18 In 1995 a fire in the metro of Baku
caused 289 casualties.
Other disastrous fires in metros occurred 1903 in Paris
(84 casualties) and 1987 in London (Kings cross station,
the fire cost 31 lifes).
Between 1978 and 1999, 97 casualties resulted from
accidents in tunnels.
In 1999 12 people died in the Tauern-tunnel and the
Montblanc-tunnel disaster claimed 41 lives.
Reasons of the Montblanc disaster :
Obsolete (old) ventilation system
Inefficient warning systems
Insufficient communication between the French and the
Italian sides
When the fire broke out only one fireman was on duty.
32. 32
Illumination of road tunnels
Road tunnels must be sufficiently illuminated. The
luminance is gradually reduced from the portal towards
the interior of the tunnel.
33. 33
Drainage
The interaction of a tunnel with the groundwater via its
drainage is a very important issue The following waters
should be collected and diverted:
Groundwater (for ecological reasons the withdrawal of
groundwater should be as low as possible)
Day water (precipitation or melting ice entering from
the portals)
Service water (e.g. from washing).
