Immersed tube tunnel is an alternative to bridges and bored tunnels for the crossing of harbors/rivers. Different strategies were considered for the construction of the immersed tunnels in India from different projects around the world during the project.

1. K

2. INTRODUCTION
TUNNEL:
• A tunnel is an underground or underwater passageway, dug
through the surrounding soil/earth/rock and enclosed except for
entrance and exit, commonly at each end. A pipeline is not a
tunnel.
• A tunnel may be for foot or vehicular road traffic, for rail
traffic, or for a canal.
• Some tunnels are used to to supply water for consumption or
for hydroelectric stations or are sewers. Utility tunnels are used
for routing steam, chilled water, electrical power or
telecommunication cables, as well as connecting buildings for
convenient passage of people and equipment.

3. WHAT ARE IMMERSED TUNNELS?
 An immersed tube(IMT) is a kind of underwater tunnel composed
of segments, constructed elsewhere and floated to the tunnel site
to be sunk into place and then linked together.
 They are commonly used for road and rail crossings of rivers,
estuaries and sea channels/harbours.
INTRODUCTION

4. IMMERSED TUNNEL

5. CONSTRUCTION STEPS:
 DESIGN AND CASTING OF TUNNEL
 DREDGING
 TOWING
 INSTALLATION OF IMT IN TRENCH
PROFILE
 BACKFILLING AND COVERING OF IMT
 MAINTENANCE

6. CASTING:
 Casting is done on the dry
dock with suitable design
required at the tunnel site
After casting tunnel
elements are temporarily
closed with bulkheads

7. DREDGING:
 The dredging method is selected to reduce the extent of
sedimentation spill and to ease handling of obstacles, such as
rock in the trench most of the dredging process is done by
mechanical process.

8. TOWING:
operational safety The EIA Sydhavnsgade Station.
 Casted tunnels at dry dock are towed to the tunnel site with
the help of tug boats before towing a system of ballast
tanks are installed inside the element

9. IMMERSION OF TUNNEL ELEMENT:
 The immersion starts by filling
the ballast tanks with water
 During the immersion
operation, the tunnel element is
held in position by the two
pontoons using suspension
wires
Gravel bed is
provided for to
reduce sediment
particles

10. BACKFILLING WITH SAND:
Once a tunnel element has been installed in the trench it is
backfilled with suitable materials and a protection layer of
approximately 1.2 m on top is provided so that it can resist to
any environmental damages and also it can tightly held in one
position .

11. TYPE OF CROSS SECTIONS:
 Circular section
 Binocular section
 Rectangular section

12. DEVELOPMENT OF CASTING
TECHNIQUES
 Steel Immersed Tube Tunnel
 Concrete Immersed Tube Tunnel
 New Technique of Full Face Casting

13. ADVANTAGES :
 The main advantage of an immersed tube is that they can be
considerably more cost effective than alternative options i.e. a
bridge
 Their speed of construction
 Minimal disruption to the river/channel, if crossing a shipping
route
 Resistance to seismic activity
 Safety of construction (for example, work in a dry dock )

14. CASE STUDY:
 The Busan – Geoje Fixed Link is a road connection between the
metropolis of Busan and Geoje Island.
 The total length of the immersed tube is 3.24 km and the water depth
is over 35 m.
 It divided into 18 elements of about 180m in length. The tunnel width
is 26.5 m and the height is 9.75 m.
 The tunnel cross section is made up of three cells in which two-lane
traffic tubes in each direction and one for the road ventilation and the
electrical and mechanical systems.
Busan – Geoje Fixed Link

15.  The casting yard is located at Anjeong inside the Jinhae Bay and
it can cast four elements at a time with full section casting.
Mooring area is provided for mooring up to 8 elements in order
to have a continuous production of tunnel elements in the casting
yard

16. Drogden Tunnel
 The connection between the artificial island of Peberholm and the
artificial peninsula at Kastrup on Amager island – the nearest
populated part of Denmark – is through the Drogden Tunnel
(Drogdentunnelen).
 The 4,050 m (13,287 ft) long tunnel comprises a 3,510 m (11,516
ft) undersea tube tunnel plus 270 m (886 ft) entry tunnels at each
end.
 The tube tunnel is made from 20 prefabricated reinforced concrete
segments – the most massive in the world at 55,000 tonnes each –
interconnected in a trench dug in the seabed.
 Two tubes in the tunnel carry railway tracks; two more carry roads
while a small fifth tube is provided for emergencies.

17. AERIAL VIEW OF THE DROGDEN
TUNNEL

18. CONCLUSION:
 The overall comparison of the immersed tunnel with the other
technical alternatives highlights the advantages of the immersed
tunnel. The immersed tunnel is the best solution because:
 There is no potential collision risk for shipping during its operation,
because it runs underneath the seabed. Furthermore, it will not affect
the water exchange across the Sea.
 It constitutes a safe and comfortable solution for traffic, offering
escape routes every 100 metres along all four tunnel tubes. Use of
the tunnel will constitute a higher safety level for road as well as for
rail compared to the safety level in the open land
 Its main environmental effects are confined to the construction
period, which means that it has little long-lasting or permanent effect
on the environment and that no severe environmental detrimental
effects can be expected