SUBMERGED TUNNELUNDERWATER TUNNELING

BY RIJWI GHOSH1EW10CV060

Under the Guidance ofMr. Nagaraja Gupta MS

Associate ProfessorDept. of Civil Engineering

East West Institute of Technology

Bangalore-560091

UNDER WATER TUNNELLING

An underwater tunnel is a passage, gallery, or roadway beneath a body of water. Underwater tunnels are used for highway traffic, railroads, and subways; to transport water, sewage, oil, and gas; to divert rivers around dam sites while the dam is being built; and for military and civil defence purposes.

Modern underwater tunnelling begins by constructing an immersed tube within a pre-dug trench on the river or sea floor. To do this, prefabricated sections of steel tube are floated into position and strategically sunk into the trench.

Types of Underwater Tunnels

Soft Ground Tunnel or Bored Tunnel

Immersed Tunnels or Submerged Tunnels

Submerged Floating Tunnels

Overview of forces acting on each type:

What is a SUBMERGED TUNNEL???What is a SUBMERGED TUNNEL???

A Submerged Tunnel is a tunnel that floats in water, supported by its buoyancy(specifically, by employing the hydrostatic thrust, or Archimedes' Principle).The tube is placed underwater, deep enough to avoid water traffic and weather, but not so deep that high water pressure needs to be dealt with—usually 20–50 m (60–150 ft.) is sufficient. Cables either anchored to the Earth or to pontoons at the surface prevent it from floating to the surface or submerging, respectively.

Why this ?Why this ?

The big advantage of a floating submerged tunnel compared to a bridge is the lightly loaded constructionlightly loaded construction. . Under water a weight reduction takes place which lowers the loads to be carried by the tunnel.

Flexible submerged tunnel has much less problems with less problems with earthquakesearthquakes which can happen in this area.

Floating tunnel can be built fast from both shores having no no problems with wind or high seasproblems with wind or high seas.

Another possible advantage is space: the downward ramp leading to a tunnel leaves a smaller footprint compared to the upward ramps required by most bridges.

Moreover traffic can run very fast through this tunnel compared to ferry link.

Due to lesser contact with the sea bed it has lesser possibilities of chemical reaction with the construction material & the sea bad soil strata.

Submerged tunnels can be placed immediately beneath a waterway. In contrast, a bored tunnel is usually only stable if its roof is at least its own diameter beneath the water. This allows Submerged tunnel approaches to be shorter and/or approach gradients to be flatter - an advantage for all tunnels, but especially so for railways.

How this is constructed…….

A trench is dredged in the bed of the water channel.

DREDGINGDredging technology has improved considerably in recent years, and it is now possible to remove a wide variety of material underwater without adverse effects on the environment of the waterway.

Tunnel elements are constructed in the dry, for example Tunnel elements are constructed in the dry, for example in a casting basin, a fabrication yard, on a ship-lift in a casting basin, a fabrication yard, on a ship-lift platform or in a factory unit.platform or in a factory unit.

casting basin fabrication yard

ship-lift platform factory unit

Materials used:As the tunnel is situated at a depth of 20-50m, it should be perfectly water tight and secondly it should resist the salty sea water and thirdly it should be withstand against hydrostatic forces coming on it.  

It is made of 4 layers. Outermost layer is constructed of aluminium to resist the salty sea water. Second and third layer is made of the super-buoyant foam to float the tunnel easily in water. Fourth layer is of concrete which gives strength to the tunnel.

After Casting…..After Casting…..

After casting the ends of the element are then temporarily sealed with bulkheads.

Each tunnel element is transported to the tunnel site - usually floating, occasionally on a barge, or assisted by cranes.

The immersion of the tunnel element is carried out after the tunnel element has been moved and the element has been ballasted as necessary to provide adequate loads in the immersion tackles.

The tunnel element is lowered to its final place on the bottom of the dredged trench.

The new element is placed against the previous element under water. Water is then pumped out of the space between the bulkheads. Water pressure on the free end of the new element compresses the rubber seal between the two elements, closing the joint.

Backfill material is placed beside and over the tunnel to fill the trench and permanently bury the tunnel, as illustrated in the figures.

Approach structures can be built on the banks before, after or concurrently with the Submerged tunnel, to suit local circumstances.

Submerged tunnels are sometimes perceived by newcomers to the technology as "difficult" due to the presence of marine operations.

In reality though, the technique is often less risky than bored tunneling and construction can be better controlled. The marine operations, though unfamiliar to many, pose no particular difficulties.

Case Study:

Seikan Tunnel

Channel Tunnel

Tokyo Bay Aqua-Line

Eiksund Tunnel

Seikan Tunnel (53.9 km)- world's longest undersea railway tunnel, with a 23.3 km long portion under the seabed. The track level is about 100 metres below the seabed and 240 m below sea level. It connects Aomori Prefecture on the main Japanese island of Honshu with the northern island of Hokkaido.

The Operating speed is The Operating speed is 140km/hr140km/hr

Channel Tunnel( 37.9 km)-the tube rail between ENGLAND & FRANCE world's longest undersea portion railway tunnel. The tunnel carries high-speed Eurostar passenger trains, the Eurotunnel Shuttle for road vehicles—the largest such transport in the world —and international freight trains. 

The Operating speed is The Operating speed is 160km/hr160km/hr

Tokyo Bay Aqua-Line (14 km) - With an overall length of 14 km, it includes a 4.4 km bridge and 9.6 km tunnel underneath the bay—the fourth-longest underwater tunnel in the world & world's longest undersea portion road tunnel

Eiksund Tunnel(7.7 km), world's deepest undersea road tunnel, it reaches a depth of −287 metres

Regular vs. Underwater TunnelsRegular vs. Underwater Tunnels

Regular Underwater

Average CostsAverage Costs $ 787,500,000

$6,349,500,000

Average LengthAverage Length 3.5 miles= 5.63 km

4.5miles= 7.24 km

Years BuildYears Build 1-3 3-6

http://www.eurotunnel.com/uk/

Tunnels required for higher costs of security and construction than bridges. This may mean that over short distances bridges may be preferred rather than tunnels (for example Dartford Crossing).

Bridges may not allow shipping to pass, so solutions such as the Oresund Bridge have been constructed.

Implementation of this project is very tough & requiring skilled labours & heavy machinery & facing very adverse situations.

THANK YOUTHANK YOU