UNDERWATER CONSTRUCTION

PRESENTED BY MOHAN KUMAR.P 8th Sem CIVIL ENGG 1

INTRODUCTION UNDERWATER CONSTRUCTION TECHNIQUES: 1.CAISSONS 2.COFFERDAMS

UNDERWATER CONCRETING Placement Methods 1. TREMIE 2. PUMP METHOD

3. TOGGLE BAGS 4. BAG WORKS

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

TYPES: 1. Box caisson 2. Open caisson 3. Suction caisson 4. Pneumatic caisson 3

BOX CAISSON

OPEN CAISSON

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PNEUMATIC CAISSON

SUCTION 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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COFFERDAMS temporary structure, designed to keep water and/or soil out of the excavation TYPES OF COFFERDAMS • • • •

Dikes Cellular cofferdams Rock-filled crib cofferdams Concrete cofferdams

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Suspended cofferdams

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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 11

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 • 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 Bagwork 13

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.

BAGWORK 1. 2.

Bags are made of open weave material. 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 17

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

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• 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. 21

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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THANK U

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