UNDERWATER CONSTRUCTION

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1UNDERWATER CONSTRUCTION

NATIONAL INSTITUTE OF CONSTRUCTION MANAGEMENT & RESEARCH, PUNE

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2INTRODUCTIONUNDERWATER CONSTRUCTION TECHNIQUES:CAISSONSCOFFERDAMS

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

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3CAISSONS

The term caisson has been derived from the French word CAISSEE, meaning BOX.Watertight retaining structure, permanent in nature.Large & hollow that is sunk down through the earth.

Constructed in such a manner so that the water can be pumped out.Used to work on foundation of bridge pier, building columns, construction of concrete dam or for the repair of ships.

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Working inside a Caisson

5BOX CAISSONOPEN CAISSON5

Control postPontoonBallast waterGrabGround water levelCircumferential gapShoeTYPES OF CAISSON

6SUCTION CAISSONPNEUMATIC CAISSON6More suitable for off shore construction.Upturned bucket embedded in marine sediment.Embedment achieved by pushing or by creating negative pressure.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.

7ADVANTAGES OF CAISSONSEconomic. 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

Dangers encountered:Caisson diseaseis 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 theBrooklyn 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.8

9COFFERDAMSTemporary structure, designed to keep water and/or soil out of the excavation area.

9TYPES OF COFFERDAMS

DikesCellular cofferdamsRock-filled crib cofferdamsConcrete cofferdamsSuspended cofferdams

10DEPT. OF CIVIL ENGINEERING GCET JAMMU

Working inside a Cofferdam

COMPONENTS OF COFFERDAMSheet pilingSheet 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. Bracing frameConcrete seal

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Bracing frameSheet piles

12ADVANTAGES OF COFFERDAMAllow 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.

13Comparison Between Caisson And CofferdamCAISSONPermanent structurePlan of small areaWater height more than 12m

COFFER DAMTemporary structurePlan of larger areaWater height up to 12m13

14UNDERWATER CONCRETINGPLACEMENT METHODS:14Tremie MethodPump MethodToggle BagsBagworkIt is a process in which the prepared concrete is poured below the water surface by using suitable methods.

15TREMIE METHODA 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

16PUMP METHODPumping 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.

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 1cum bags can be placed using a crane.

17Used only in special cases like repair works, etc.

UNDERWATER CONSTRUCTIONDEPT OF CIVIL ENGINEERING GCET JAMMU17

18 A CASE STUDY ON BRIDGE FOUNDATIONAkashi Kaikyo Bridge, Japan(Completed in 1998)

The two main tower foundations are large double-wall steel caissons filled with tremie concrete.

19The 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 50,000 cum of concrete was placed in the steel caisson.21

22CONCLUSION

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 casesFor massive underwater concrete construction of navigation structures, the pump method should be prohibited.

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23 THANK YOU!Presented By:

SUNAY JAISWALAP14101ANKUSH SINGHAP14125SIDDESH HUPRIKAR AP14126NITIN KUMAR AP14137AMIT SINGHAP14192