What is this???
∗ A Submerged Tunnel is a tunnel that
floats in water, supported by
its buoyancy(specifically, by employing
the hydrostatic thrust, or Archimedes'
∗ 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 ?
∗ The big advantage of a floating submerged tunnel compared to a bridge is the
lightly 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 earthquakes which can
less problems with earthquakes
happen in this area.
∗ Floating tunnel can be built fast from both shores having no problems with wind
or high seas.
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
∗ 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.
Cross Harbour Tunnel- Hong Kong,
a busy road tunnel
Regular vs. Underwater Tunnels
= 5.63 km
= 7.24 km
How this is constructed…….
∗ A trench is dredged in the bed of the water channel.
Dredging 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
∗ Tunnel elements are constructed in the dry, for example in a casting basin, a
fabrication yard, on a ship-lift platform or in a factory unit.
∗ After casting the ends of the element are then temporarily sealed
∗ 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
Water pressure on the free end of the new element compresses
the rubber seal between the two elements, closing the joint.
and over the
tunnel to fill
the trench and
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.