Underwater Construction Techniques

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

Underwater Construction Techniques:

1. Caissons
2. Cofferdams

Underwater Concreting

Placement Methods

1. Tremie
2. Pump Method
3. Toggle Bags
4. Bag Works

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

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.

Cofferdams

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

Types of Cofferdams

1. Dikes
2. Cellular cofferdams
3. Rock-filled crib cofferdams
4. Concrete cofferdams
5. Suspended cofferdams

Components of Cofferdam

1. Sheet Piling
2. Bracing Frame
3. Concrete Seal

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

Comparison Between Caisson and Cofferdam

Caisson

1. Permanent structure
2. Plan of small area
3. Water height more than 12m

Coffer Dam

1. Temporary structure
2. Plan of larger area
3. Water height up to 12m

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.