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.

What is this???What is 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.

Why this ?Why this ?

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.

Sydney Harbour Tunnel(2.8 km)

Seikan Tunnel (53.9 km)- world's longest undersea

railway tunnel

Channel Tunnel( 37.9 km)-the tube rail between ENGLAND &

FRANCE world's longest undersea portion railway tunnel

Marmaray (ISTANBUL) connecting Asia and Europe

Tokyo Bay Aqua-Line (9.6 km) world's longest undersea

portion road tunnel

Eiksund Tunnel(7.7 km), world's deepest undersea road

tunnel

Cross Harbour Tunnel- Hong Kong, a busy road tunnel

Regular vs. Underwater Regular vs. Underwater TunnelsTunnels

Regular UnderwaterAverage 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/

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

How this is constructed…….

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

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

The new element is placed against the previous The new element is placed against the previous element under water. Water is then pumped out element under water. Water is then pumped out

of the space between the bulkheads. of the space between the bulkheads. Water pressure on the free end of the new Water pressure on the free end of the new

element compresses the rubber seal between the element compresses the rubber seal between the two elements, closing the joint. two elements, closing the joint.

Backfillmaterial 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.

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.