Caisson (engineering)

Caisson_Schematic

FMIB_49991_Fixed_Apparatus,_supplied_with_Compressed_Air

Caisson (pronounced /ˈkeɪsən/) is a watertight retaining structure used in engineering and construction projects to work on the foundations of a bridge, pier, or other structures. Caissons are used when construction must occur in or near water, providing a dry working environment below the waterline.

Types of Caissons

There are several types of caissons, each suited to different construction needs and environments:

• Open Caisson: This type is open at both the top and bottom and is sunk into place by removing material from within the caisson. It is commonly used for bridge piers and other structures requiring deep foundations.
• Box Caisson: A prefabricated concrete box with a closed bottom and open top, which is floated to the site and then sunk into place by filling it with concrete or other heavy material.
• Pneumatic Caisson: This type is used in situations where the water depth is significant. It is a watertight chamber with compressed air to keep water out, allowing workers to excavate and work at the bottom.

Construction Process

The construction process of caissons involves several steps:

1. **Design and Planning**: Engineers design the caisson based on the specific requirements of the project, including the type of soil, water depth, and load-bearing needs. 2. **Fabrication**: The caisson is fabricated, often off-site, and transported to the construction location. 3. **Placement**: The caisson is placed in position, either by floating it to the site or by using cranes and other heavy machinery. 4. **Sinking**: The caisson is sunk into place by excavating material from within (open caisson) or by adding weight (box caisson). 5. **Sealing and Construction**: Once in place, the caisson is sealed, and construction can proceed within the dry environment it provides.

Applications

Caissons are used in various construction projects, including:

• Bridge foundations
• Pier construction
• Dock and harbor construction
• Underwater tunnels

Advantages and Disadvantages

Advantages

• Provides a dry working environment in underwater construction.
• Can be used in deep water and difficult soil conditions.
• Offers a stable and secure foundation for heavy structures.

Disadvantages

• High cost and complexity of construction.
• Requires specialized equipment and skilled labor.
• Potential risks to workers, especially in pneumatic caissons due to decompression sickness.

Related Pages

• Bridge
• Pier
• Dock
• Underwater tunnel
• Foundation (engineering)