It is a process in which the prepared concrete is poured below the water surface by using suitable methods.
Underwater Construction Techniques:
- Pump Method
- Toggle Bags
- Bag Works
- Permanent structure.
- Large hollow structure that is sunk down through the earth
- Used in the construction of bridge piers, building columns, dams.
- Box caisson
- Open caisson
- Suction caisson
- Pneumatic caisson
Advantages of Caissons
- 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.
Temporary structure, designed to keep water and/or soil out of the excavation.
Types of Cofferdams
- Cellular cofferdams
- Rock-filled crib cofferdams
- Concrete cofferdams
- Suspended cofferdams
Components of Cofferdam
- Sheet Piling
- Bracing Frame
- 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
- Permanent structure
- Plan of small area
- Water height more than 12m
- Temporary structure
- Plan of larger area
- Water height up to 12m
- 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.