Under water construction

1. Presented by:
Abira Rather
7th sem
Civil Eng. Dept.
R.no: 07/10
Underwater
construction
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DEPT. OF CIVIL ENGINEERING GCET JAMMU

2. Contents:
 Introduction
 Underwater construction techniques
 Caissons
 Types
 Advantages
 Dangers encountered
 Cofferdams
 Types
 Components
 Advantages
 Underwater lying of concrete
 Tremie method
 Pump method
 Toggle bags
 Bagwork
 Conclusion
 References
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DEPT. OF CIVIL ENGINEERING GCET JAMMU

3. During the construction of brides , 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.
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DEPT. OF CIVIL ENGINEERING GCET JAMMU

4. UNDERWATE
R
CONSTRUCTI
ON
Constructi
on
techniques
Caissons
Cofferdam
s
Methods
of Placing
of concrete
Tremie
method
Pump
method
Toggle
bags
Bag works
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DEPT. OF CIVIL ENGINEERING GCET JAMMU

5. Caissons:
Watertight retaining structure .
Permanent in nature.
Used to work on foundation of bridge pier,
construction of concrete dam or for the repair of
ships.
Constructed in such a manner so that the water can be
pumped out.
Keeps working environment dry.
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6. 6
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Working inside a caisson

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Control post
pontoon
Ballast water
grab
Ground
water
level
Circumferential
gap
shoe
Box caisson
Open caisson
TYPES OF CAISSONS

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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 quicksand's.

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• More suitable for off shore construction.
• Upturned bucket embedded in marine sediment.
• Embedment achieved by pushing or by creating negative
pressure.
Suction caisson

10. 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
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DEPT. OF CIVIL ENGINEERING GCET JAMMU

11. Dangers encountered:
Caisson disease is so named since it appeared in
construction workers when they left the compressed
atmosphere of the caisson and rapidly re entered
normal (decompressed) atmospheric conditions.
Construction of the Brooklyn Bridge, which was built
with the help of caissons, resulted in numerous
workers being either killed or permanently injured by
caisson disease during its construction, including the
designer's son and Chief Engineer of the project.
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DEPT. OF CIVIL ENGINEERING GCET JAMMU

12. Cofferdams:
Temporary structure
Built within or in pairs across a body of water
Allows the enclosed space to be pumped out, creating a dry
work environment .
Enclosed coffers are commonly used for construction and
repair of oil platforms, bridge piers and other support
structures built within or over water.
A cofferdam involves the interaction of the structure, soil,
and water. The loads imposed include the hydrostatic forces
of the water, as well as the dynamic forces due to currents
and waves.
Used for shallow constructions having depth less than 10m.
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DEPT. OF CIVIL ENGINEERING GCET JAMMU
Working inside a cofferdam

14. Components of cofferdam:
 Sheet piling
Sheet piling is a manufactured
construction product with a
mechanical connection
“interlock” at both ends of the
section. These mechanical
connections interlock with one
another to form a continuous
wall of sheeting.
 Brace piling
 Concrete seal
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DEPT. OF CIVIL ENGINEERING GCET JAMMU
Bracing frame
Sheet piles

15. COFFERDAM CONSTRUCTION SEQUENCE:
1. Pre-dredge to remove soil or soft sediments and level the area of the
cofferdam
2. Drive temporary support piles.
3. Temporarily erect bracing frame on the support piles
4. Set steel sheet piles.
5. Drive sheet piles to grade.
6. Block between bracing frame and sheets, and provide ties for sheet
piles at the top as necessary
7. Excavate inside the grade or slightly below grade, while leaving the
cofferdam full of water
8. Drive bearing
9. Place rock fill as a levelling and support course.
10. Place Tremie concrete seal . DEPT. OF CIVIL ENGINEERING GCET JAMMU
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16. ADVANTAGES OF COFFERDAM:
Allow excavation and construction of structures in
otherwise poor environment.
Provides safe environment to work.
Contractors typically have design responsibility.
Steel sheet piles are easily installed and removed.
Materials can typically be reused on other projects.
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DEPT. OF CIVIL ENGINEERING GCET JAMMU

17. UNDERWATER CONCRETING
PLACEMENT
METHODS:
Tremie method. Pump method. Toggle bags. Bags work.
It is a process in which the prepared concrete is
poured below the water surface by using
suitable methods.
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DEPT. OF CIVIL ENGINEERING GCET JAMMU

18. TREMIE METHOD
A Tremie is a watertight pipe
Generally 250mm in dia.
Funnel shaped hopper at its upper end
and a loose plug at the bottom.
It is supported on a working platform
above water level.
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19. Laying of concrete by using Tremie
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Basic principle behind Method
of underwater concreting -
Tremie method
Method of underwater
concreting— Tremie
method (inside view)

20. Specifications of concrete to be
used in Tremie method:
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 Coarse Aggregate: Gravel of 3/4” (20mm) max. size. Use 50-55 %
of the total aggregate by weight.
 Sand, 45-50% of the total aggregate by weight.
 Cement: Type II ASTM (moderate heat of hydration), 600 lbs./yd3
 Water/Cement Ratio: 0.42 (0.45 Maximum).
 Water-Reducing Admixture (preferably it is also plasticizer): Do not
use super plasticizers.
 Air-Entrainment Admixtures: To give 6% total air.
 Retarding Admixture: To increase setting time to 4-24 hours, as
required.
 Slump: 6 1/2" ± 1"
 This mix will develop compressive strength in the range of 5,600 –
7,000 psi at 28 days.

21. 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 time and labour.
 For massive underwater concrete
construction of navigation structures,
the pump method should be
prohibited.
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PUMP METHOD OF LAYING
CONCRETE

22. TOGGLE BAGS:
• 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.
BAGWORK:
• 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.
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Used only in special cases like repair works, etc.

23. 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.
 At present, the Tremie placement method is the standard way of placing
high-quality concrete underwater. 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.
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24. ANY QUESTIONS??
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25. THANK YOU!!
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