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PRESENTED BYMOHAN KUMAR.P8th Sem CIVIL ENGG

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INTRODUCTIONUNDERWATER CONSTRUCTION TECHNIQUES:1.CAISSONS2.COFFERDAMS

UNDERWATER CONCRETINGPlacement Methods1. TREMIE 3. TOGGLE BAGS2. PUMP METHOD 4. BAG WORKS

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CAISSONSPermanent structure.Large hollow structure that is sunk down through the earth Used in the construction of bridge piers, building columns, dams.

TYPES:1.Box caisson2.Open caisson3.Suction caisson4.Pneumatic caisson

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BOX CAISSON

OPEN CAISSON

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SUCTION CAISSON

PNEUMATIC CAISSON

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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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Working inside the caisson foundation

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COFFERDAMStemporary structure, designed to keep water and/or soil out of the excavation

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TYPES OF COFFERDAMS• Dikes• Cellular cofferdams• Rock-filled crib cofferdams• Concrete cofferdams• Suspended cofferdams

DRY WORKING AREA

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COMPONENTS OF COFFERDAM

o SHEET PILING

o BRACING FRAME

o CONCRETE SEAL

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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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Comparison Between Caisson And Cofferdam

CAISSON• Permanent structure• Plan of small area• Water height more

than 12m

COFFER DAM• Temporary structure• Plan of larger area• Water height up to

12m

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UNDERWATER CONCRETING

PLACEMENT METHODS:

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• Tremie method• Pump method• Toggle bags• Bagwork

• It is a process in which the prepared concrete It is a process in which the prepared concrete is poured below the water surface by using is poured below the water surface by using suitable methodssuitable methods

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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.

Fig: schematic of a tremie method

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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 labor.

• For massive underwater concrete construction of navigation structures, the pump method should be

prohibited.

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TOGGLE BAGS 1. Toggle bags are ideal for small amounts of concrete placement. 2. They are bag is filled in the dry with wet concrete 4. Used for repair work. 3. The concrete is squeezed out by a diver.

BAGWORK1. Bags are made of open weave material.2. Diver-handled bags are usually of 10 to 20 litres capacity but 1

m3 bags can be placed using a crane.

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A CASE STUDY ON BRIDGE FOUNDATION

Akashi Kaikyo Bridge, Japan

(Completed in 1998)

The two main tower foundations are large double-wall steel

caissons filled with tremie concrete

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• The project required that a large volume of tremie concrete be placed up to 57m below the water surface

CASE STUDY

• All the tremie concrete was produced on a floating batch plant • Each tremie placement was carried out

continuosly day and night for 3days.• Each tremie pipe covered a 100-m2 area.

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• The total of 50,000m3 of concrete was placed in the steel caisson.

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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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REFERENCES

1) “ underwater concrete”- by Dr Jagadish.R.2) “ Foundation engineering”- by R. B. Peck, W. E Hanson, T.H.

Thornburn.3) “Concrete technology” – by M S Shetty.

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