Underwater construction

1 Presented by:Abira Rather 7th sem Civil Eng. Dept.R.no: 07/10

Underwater construction

DEPT. OF CIVIL ENGINEERING GCET JAMMU

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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


3 Introduction:

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.DEPT. OF CIVIL ENGINEERING GCET JAMMU

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UNDERWATER CONSTRUCTION

Construction techniques

Caissons

Cofferdams

Methods of Placing of concrete

Tremie method

Pump method

Toggle bags

Bag worksDEPT. OF CIVIL ENGINEERING GCET JAMMU

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Underwater construction techniques:

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.DEPT. OF CIVIL ENGINEERING GCET JAMMU


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Working inside a caisson

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Control post

pontoon

Ballast watergrab

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


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.

12Cofferdams:

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.DEPT. OF CIVIL ENGINEERING GCET JAMMU


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Working inside a cofferdam

14Components 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


Bracing frame

Sheet piles

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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


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.

17UNDERWATER 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.


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.


Laying of concrete by using Tremie 19


Basic principle behind Method

of underwater concreting -

Tremie method

Method of underwater concreting— Tremie method (inside view)

http://4.bp.blogspot.com/-xHzca8gtbqE/T5MJS-esDkI/AAAAAAAABzA/Tt-tkeZuh3Y/s1600/Method_of_underwater_concreting_Tremie_method.jpg

20Specifications of concrete to be used in Tremie method:


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.


PUMP METHOD OF

LAYING CONCRETE

22TOGGLE 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.


Used only in special cases like repair works, etc.

23CONCLUSION:

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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ANY QUESTIONS??


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THANK YOU!!


Education

Underwater construction