3. 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.
5. UNDERWATER CONSTRUCTION
TECHNIQUES
CAISSONS
Watertight retaining structure
Permanent in nature
Used to work on foundationof bridge pier, construction of
concrete dam or for therepair of ships
Constructed in such a manner so that the water can be
pumped out
Keeps working environment dry.
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9. TYPES OF CAISSONS
OPEN CAISSON
BOX CAISSON
PNEUMATIC CAISSON
SUCTION CAISSON
10. OPEN CAISSON
Similar to box but does not have bottom face .
Used in soft clays not having large obstructions
beneath.
It may fill with water during sinking.
14. BOX CAISSON
Prefabricated concrete box , it is set down on
prepared bases.
Once in place it is filled with concrete to
become part of the permanent works.
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17. PNEUMATIC CAISSON
Large inverted box on which pier is built.
Compressed air is used to keep the water and
mud out.
Used to work on riverbed or quicksands.
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21. SUCTION CAISSON
More suitable for off shore construction.
Upturned bucket embedded in marine sediment.
Embedment achieved by pushing or bycreating
negative pressure.
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28. ADVANTAGES OF CAISSONS
Economic.
Slightly less noise and reduced vibrations.
Easily adaptable to varying site conditions.
High axial and lateral loading capacity.
Minimal handling equipment is required for
placement of reinforcing cage.
Placement is sometimes possible in types of soil
that a driven pile could not penetrate.
29. DANGERS ENCOUNTERED
CAISSON DISEASE is so named since it appeared
in construction workers when they left the
compressed atmosphere of the caisson and
rapidly reentered normal (decompressed)
atmospheric conditions.
Construction of the Brooklyn Bridge , which was
built with the help of caissons , resulted in
numerousworkers being either killed or
permanently injured bycaisson diseaseduring its
construction, including thedesigners son and Chief
Engineer of the project.
33. COFFER DAM
Coffer dams are temporary enclosures to keep out
water and soil so as to permit dewatering and
construction of the permanent facility in the dry
Meaning of Coffer Dam :Coffer=Box
To take up the foundation works in the Marine
Region, it is necessary to obstruct the water
f low by means of Coffer Dam.
34. PURPOSE TO USE COFFER DAM
STRUCTURE
To retain Soil & Water
Can be used as either Temporary or Permanent
Main purpose is to provide dry working area for
workers
It is constructed to facilitate piledriving operations.
theraft
It is used to place grillage as well as
foundation
It is used, whenthe foundation for piers and
abutments of a bridge , dams, locks, etc.. are tobe
constructed.
Some times it is also provided to storewater
temporarily
35. Cofferdams can be used in the all
sectors as explained below
A. Civil Engineering: Underground Car Parking,
Foundation, Basement Construction
B. Transport Engineering: Bridge Pier, Support Wall,
Ramps, Ground Water Retention, Tunnel Worketc.
C. Water Engineering: Weirs, Culverts, Flood
Protection Walls, Scour Protection Walls,Securing
Embankmentetc..
D. Port Construction: Dock Works, Jetty Worksetc..
36. TYPES OF COFFERDAM
1. Earth fill cofferdams: Mainly for low level water
2. Sand Bag Coffer Dam: Todivertcoarse of water
3. Rock fill cofferdams
4. Timber Cribor Rock filled cribcofferdams
Construction on land and than f loated into place,
which is also known as Gravity Dam
5. Braced/Sheet Pile Coffer Dam: Consisting of Sheet Piles,
mainly used in shallow water depth
a) Single wall cofferdams
b) Double wall cofferdams
c) Cellular cofferdams
6. Movable or Suspendedcofferdams
37. UNDERWATER CONCRETING
It is a process in which the prepared concrete is
poured below the water surface by using suitable
methods.
PLACEMENT METHODS
TREMIE METHOD
PUMP METHOD
TOGGLE BAGS
BAGS WORK
38. TREMIE METHOD
A Tremie is a watertight pipe
Generally 250mm in Dia
Funnel shaped hopperat its upper end and a
loose plug at the bottom
It is supported on a working platform above water
level
39. PUMP METHOD
Pumping concrete directly into its final position,
involving both horizontal and vertical delivery of
concrete.
Pumping concrete has the advantage of operational
efficiency with potential savings of timeand labour.
For massive underwater concrete construction of
navigation structures , the pump method should
be prohibited.
40. TOGGLE BAGS BAG WORK
Toggle bags are ideal for
small amounts of concrete
placement.
The bag is filled in the dry
with wet concrete.
Used for repair work.
The concrete is squeezed
out by a diver.
Bags are made of open
weave material.
Diver- handled bags are
usually of 10 to 20 litres
capacity but 1cub . m bags
can be placed using a
crane.
41. CONCLUSION
Cofferdams are temporary structures and used in
cases where the plan area of foundation is very
large, depth of water is less and for the soft soils,
where soils allow easy driving of sheet piles.
Caissons are permanent structures and becomes
economical in cases where the plan area of
foundation is small, large depth of water and for
loose soils.
Suction caisson anchors are gaining considerable
acceptance in the offshore industry.
42. At present, the Tremie placement method is the
standard way of placing high-quality concrete.The
other placement method are not able to reliably
place high- quality underwater concrete for major
structures, although they may find application in
special cases.
For massive underwater concrete construction of
navigation structures, the pump method should be
prohibited.