Underwater construction requires specialized techniques to create a dry environment for building in conditions of high water pressure. Common methods include using caissons or cofferdams to exclude water from the construction site, and placing concrete must be done using tremie pipes or pumps to prevent contamination. The shape of underwater structures is influenced by withstanding immense water pressure, with domes and arches able to support large spans. Major tunnels built through this method include the Holland Tunnel under the Hudson River and the submerged floating tunnel in Tokyo Bay.

1. UNDERWATER CONSTRUCTION

2. INDTRODUCTION
• During the construction of bridges, dams or any
other structure where the foundation part of the
structure is most likely to lie underwater , we have
to opt for underwater construction
• Construction in water poses many difficulties
especially in the places where there the depth is
considerable.
• During underwater construction our main objective
is to create dry and water free environment for
working in such a manner that the structural
stability of the structure is not compromised.

3. HOW IT ACT AS FOUNDATION
• Underwater construction works as observed by the
engineers and designers are considered as the most
difficult work. Caissons are sunk through ground or water
to exclude water and semi-fluid material during the process
of excavation of foundations and which subsequently
becomes an integral part of the substructure.
• Underwater foundations, also known as
subaqueous foundations, may be used in situations where
the use of a cofferdam or caisson is prohibitively expensive
or unfeasible. ... If the foundation is relatively short and in
shallow water, bagged concrete or cement placed in layers
may be used as formwork and left in position.

4. UNDERWATER CONSTRUCTION
TECHNIQUES
• Dry Construction
• Wet Construction

5. DRY CONSTRUCTION
1.CAISSON
• Water tight retaining structure.
• Permanent in nature.
• Used in construction of bridges,
piers,dams,etc.
• Constructed in a way
water can pumped out.
TYPES :
1. Open Caisson
2. Box Caisson
3. Suction Caisson

6. ADVANTAGES OF CAISSON
• Economic.
• Slight less noise and reduced vibrations.
• Easily adaptable to varying site conditions.
• High axial and lateral loading capacity.

7. 2.COFFERDAMS
•Temporary structure.
•Built across body of water.
•Involves interection of
structure,soil and water.
•Creates a dry work
environment.
COMPONENTS:
1. Sheet Piling
2. Brace Piling
3. Concrete Seal

8. ADVANTAGES OF COFFERDAM
• Provides safe environment to work.
• Contractors have design responsibily.
• Steel sheet piles are easily installed and
removed
• Materials typically reused on other projects.

9. WET CONTRUCTION
• Evaculate the overall cost of the work.
• Considering time
• Equipment needs
• The capability of a diver to accomplish the
specific task.
• A more gross than fine nature.

10. TECHNIQUES FOR CONCRETING
UNDER WATER
• Use pre-cast concrete units and lower into
place
– Light enough to place
– Heavy enough to stay in place – or anchor
• Place wet concrete inside sacrificial bag
• Use a hopper with a bottom gate & skirt
• Use tremie pipe or flexible hose

11. TREMIE PIPE –
FOR SMALL QUANTITIES ONLY
• Crumpled paper used to
block tube initially
• Fresh concrete placed
within existing mass
• Formwork required – can
be pre-cast units
• Scour may be a problem
• Cofferdams can provide
protection
• Can use flexible hose &
pumped concrete
Water
level
Sea bed
level
Fresh
concrete in
hopper

13. PUMP METHOD
• Pumping concrete directly
into its final position ,
involving both horizontal
and vertical delivery of
concrete.
• Operational efficiency
with potential savings of
time and labour.
• For massive underwater
concrete construction of
navigation structures , the
method is prohibited.

14. TOGGLE BAGS
• Used for the placement of
small amounts of
concrete.
• Bag is filled in dry
condition with wet
concrete.
• Used mainly for repairing
works.
• Concrete is squeezed out
from the bag by the diver.

15. SHAPE RELATED TO PRESSURE
• The biggest challenge for
an underwater structure is
withstanding the constant
water pressure.
• To understand how these
structures solve this
problem we have to have
a better understanding of
the forces at play.

16. • Pressure is a force divided by the
area the force is acting on.
• The force of this pressure is
exerted perpendicular to the
surface on the object.
• The illustrations on the right are
based on a gas pressure from
inside the object, but the
principles work the same with
water pressure from the outside.
• The amount of water above the
object and the resulting pressure
on the object have a linear
relationship.
• Domes and arches are derived
from a spherical shape and are
therefore used in architecture
when dealing with large spans or
high carry loads.

17. SHAPE RELATED TO MATERIAL
• Pressure from the outside compresses the material
while pressure from inside of the object stretches
the material.
• This difference is very important, because materials
have different compressive and tensile strengths.
• Material used
• Steel concrete
• acrylic glass

18. SUBMERGED FLOATING TUNNEL
• LOCATION : Tokyo Bay Aqua – Line ( 9.6 km )

19. • Submerged floating tunnel is basically making a tunnel
to float underwater which is balanced by its buoyancy,
self weight and constraint forces resulted from cable
system and thus submerged to a certain depth
underwater.
• The tube is placed underwater, deep enough to avoid
water traffic and weather, but not so deep that high
water pressure needs to be deal with, usually 20 m to
50 m is sufficient.

20. CONSTRUCTION
• A trench is dredged in the bed of water
channel.
DREDGING :
• 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 waterway.

21. PROCEDURE
• Construction of tunnel
segments on dry dock.
• Transporting the tunnel
segmenets to their final
places and placing the
underwater.
• Joinning of different tunnel
segments by using rubber
gasket.
• Anchoring the tunnel to
the cables.

22. STEP 1 : PRECASTING
• Huge tunnel section are constructed on dry dock.
• The procedure consists same as that of precast
construction.
• Dry dock is flooded and the panels are transported to
their respective places.
• Sinking of tunnel is controlled by the use of ballast
tank as in case of submarines.

23. STEP 2 : JOINTS
• After the submersion of different panels in
water they are connected with one another by
using a rubber gasket.
• Another procedure includes trapping of water
between the joints and then removing it
afterwards.

24. STEP 3 : FOUNDATION
• The application consists same as that of in caission
foundation.
• A hollow chamber is penetrated down the sea bed as
shown which evacuates the water trapped inside it
by a valve present on its top surface.
• Such type of foundations are been used for the
offshore oil rig plants.

25. STEP 4 : ANCHORING OF CABLES
• After the foundation work is completed, the
cables are anchored to the floating tunnel
which will avoid its movement and will place it
firmly in alignment.
• This operation can be carried out by drivers.
• Finally the tunnel will be in position and ready
to use.

26. MATERIAL USED
• As the tunnel is situated at a depth of 30 m.
• It should be perfectly water tight and secondly it
should resist the salty sea water thirdly it should
withstand against hydrostatic forces coming on it.
• It made of 4 layers.
• Outermost layer is constructed of aluminium to
resists the salty sea water.
• Second and third layer is made of the foam to float
the tunnel easily in water.
• Fourth layer is of concrete which gives strength to
the tunnel.

27. •The holland tunnel was built (1920-1924) by
pneumatically pushing cylindrical shields through the
river bottom.
• The shields not only dug through mud but also served
as the shell beneath which the actual tunnel walls (built
of iron rings filled with concrete) were constructed.
THE HOLLAND TUNNEL

28. • The Holland Tunnel opened in 1927 as the first
underwater vehicular crossing of the Hudson River
between Manhattan and Jersey City, New Jersey.
• It is the first tunnel constructed with a ventilation
system specifically designed to handle automobile
and truck exhaust fumes.
• By the 20th century, trains and cars had replaced
canals as the primary form of transportation
• The Holland Tunnel, completed in 1927, was one of
the first roadway tunnels and is still one of the
world's greatest engineering projects.
• Named for the engineer who oversaw
construction, the tunnel ushers nearly 100,000
vehicles daily between New York City and New
Jersey.

29. • Eleven different plans for the
tunnel were proposed,
including a design by General
George W. Goethals that
included a single tube lined
with concrete blocks having
two levels, each containing
three traffic lanes.
• experiments were conducted
to provide the data necessary
to design the special
ventilation system for motor
vehicle exhaust.
• Holland's plan called for twin
tubes lined with cast iron, each
containing two lanes of traffic
on a single deck, and was
ultimately selected.

30. • This type of longitudinal system would not work in
a vehicular tunnel because it would require gale
force winds of more than 70 miles per hour (113
km/h)
• a new type of ventilation system was devised in
which clean air would be supplied throughout the
tunnel through a fresh air duct located below the
roadway with openings.
• An exhaust duct would be located above the
roadway with openings at regular intervals to
remove the diluted exhaust fumes out of the
tunnel.
• large cylinder driven by 30 hydraulic jacks with a
total force of 6,000 tons (5,400 t).
• excavated, 2.5 foot (76 cm) thick cast iron rings are
added to support the walls.

31. Tunnel Construction: Soft Ground
and Hard Rock
• Workers generally use two
basic techniques to
advance a tunnel.
• In the full-face method,
they excavate the entire
diameter of the tunnel at
the same time.
• The second technique, is
the top-heading-and-bench
method.

32. • In this technique, workers dig a smaller tunnel
known as a heading.
• Once the top heading has advanced some distance
into the rock, workers begin excavating
immediately below the floor of the top heading;
this is a bench.
• One advantage of the top-heading-and-bench
method is that engineers can use the heading
tunnel to gauge the stability of the rock before
moving forward with the project.

33. Soft Ground (Earth)
• Workers dig soft-ground tunnels through clay, silt,
sand, gravel or mud.
• In this type of tunnel, stand-up time -- how long the
ground will safely stand by itself at the point of
excavation -- is of paramount importance.
• Because stand-up time is generally short when
tunnelling through soft ground, cave-ins are a
constant threat.
• To prevent this from happening, engineers use a
special piece of equipment called a shield.

34. • It carves a perfectly round
hole and supports the
surrounding earth.
• While workers remove debris
and install a permanent lining
made of cast iron or precast
concrete.

35. Hard Rock
• Tunnelling through hard rock almost always involves
blasting.
• Workers use a scaffold, called a jumbo.
• The jumbo drills mounted to make several holes in
the rock.
• The depth of the holes can vary depending on the
type of rock, but a typical hole is about 10 feet deep
and only a few inches in diameter.

36. • Then they repeat the process.
• Fire-setting is an alternative to blasting.
• In this technique, the tunnel wall is heated with fire,
and then cooled with water.
• In this environment, extra support for the tunnel roof
and walls may not be required.
• However, most tunnels pass through rock that
contains breaks or pockets of fractured rock, so
engineers must add additional support in the form of
bolts, sprayed concrete or rings of steel beams. In
most cases, they add a permanent concrete lining.

37. Tunnel Construction: Soft Rock
and Underwater
• Tunneling through soft rock and
tunneling underground require
different approaches.
• Blasting in soft, firm rock such
as shale or limestone is difficult
to control.
• The circular plate is covered
with disk cutters -- chisel-
shaped cutting teeth, steel disks
or a combination of the two.

38. • As the circular plate slowly rotates, the disk cutters
slice into the rock, which falls through spaces in the
cutting head onto a conveyor system.
• TBMs don't just bore the tunnels -- they also provide
support.
• As the machine excavates, two drills just behind the
cutters bore into the rock. Then workers pump grout
into the holes and attach bolts to hold everything in
place until the permanent lining can be installed.
• The TBM accomplishes this with a massive erector arm
that raises segments of the tunnel lining into place.

39. • Tunnels built across the bottoms of rivers, bays and
other bodies of water use the cut-and-cover method,
which involves immersing a tube in a trench and
covering it with material to keep the tube in place.
• Construction begins by dredging a trench in the riverbed
or ocean floor.
• Long, prefabricated tube sections, made of steel or
concrete and sealed to keep out water, are floated to the
site and sunk in the prepared trench.
• Then divers connect the sections and remove the seals.
• Any excess water is pumped out, and the entire tunnel is
covered with backfill
Underwater

40. • One of the most important
concerns is ventilation -- a
problem magnified by waste
gases produced by trains
and automobiles.
• His solution was to add two additional layers above and
below the main traffic tunnel.
• The upper layer clears exhaust fumes, while the lower
layer pumps in fresh air.
• Four large ventilation towers, two on each side of the
Hudson River, house the fans that move the air in and
out.
• Eighty-four fans, each 80 feet in diameter, can change
the air completely every 90 seconds.
Tunnel ventilation tower

41. Tunnel planning
• requires very different techniques than tunneling through
hard rock or soft rock, such as shale, chalk or sandstone.
• For New York City officials, the
solution was clear: Build an
automobile tunnel under the river
and let commuters drive
themselves from New Jersey into
the city.
• 51,694 vehicles made the crossing
• an average trip time of just 8
minutes.
• the challenge was an obsolete ferry system that strained to
transport more than 20,000 vehicles a day across the Hudson
River.

42. CONCLUSION
• Cofferdams are temporary structures and used in
cases where the plan area of foundation is very
large depth of water and for loose soils.
• At present,the tremie placement method is
standard way of placing high quality concrete
underwater.
• Underwater construction is useful for power
generation,bridges,ship husbandry,water
utilities,mining,pipeline,power and gas
trasmission.
• And attracting places for tourits.