Caissons

Definition

Caissons are large, watertight structures used as foundations for bridges, buildings, and other heavy structures, typically constructed underwater or in areas with high water tables. They are designed to support the weight of the superstructure and prevent settlement by transferring loads to stable soil or bedrock beneath the water surface. Caissons can be open or closed at the top, and their construction involves excavation and placement of concrete or other materials to create a robust foundation.

5 Must Know Facts For Your Next Test

1. Caissons are often used in underwater construction projects because they can withstand water pressure and allow for dry working conditions during installation.
2. There are two main types of caissons: open caissons, which are filled with water during construction, and pneumatic caissons, which use air pressure to keep the working area dry.
3. The depth of a caisson is determined by the load it must carry and the bearing capacity of the underlying soil or rock.
4. Caissons are particularly effective in areas with unstable soil conditions, as they can provide a strong and stable foundation even in challenging environments.
5. Construction of caissons requires careful planning and engineering to ensure proper sealing against water ingress and to manage excavation safely.

Review Questions

• How do caissons function as deep foundations compared to piles and drilled shafts?
  • Caissons function as deep foundations by transferring loads from structures to stable soil or bedrock, similar to piles and drilled shafts. However, caissons are typically larger and often constructed in wet conditions, making them suitable for underwater projects. Unlike piles, which are driven into the ground, caissons involve excavating a large hole that is then filled with concrete. This allows for greater load-bearing capacity in certain applications, particularly where soil conditions may be less than ideal.
• Discuss the advantages of using caissons in construction projects over other foundation types.
  • Caissons offer several advantages over other foundation types, including their ability to provide stability in loose or saturated soils where other foundations might fail. Their large diameter allows them to support heavier loads, making them ideal for tall structures like bridges or skyscrapers. Additionally, because caissons can be built underwater, they enable construction in environments where traditional foundation methods may not be feasible. The use of caissons can also minimize settlement issues compared to shallow foundations.
• Evaluate the potential challenges faced during the construction of caisson foundations and how these might impact project timelines.
  • During the construction of caisson foundations, several challenges can arise, including water ingress that complicates excavation and increases costs. The need for specialized equipment and skilled labor adds complexity to project management. Additionally, variations in soil conditions can lead to unexpected changes in design or additional excavation requirements. These factors can significantly impact project timelines, causing delays if not adequately planned for. Proper risk assessment and contingency planning are essential to mitigate these challenges.

Related terms

Piles: Long, slender columns driven into the ground to transfer loads from structures to deeper, more stable soil or bedrock.

Drilled Shafts: Deep foundation elements created by drilling a hole into the ground and filling it with concrete to support heavy loads.

Soil Bearing Capacity: The maximum load per unit area that the soil can support without failure, crucial for determining the type of foundation to use.