Foundations are the crucial elements of any construction that offer structural support and help in effectively distributing loads. Without a stable foundation, the building cannot withstand for a long time. While various foundations are available to fulfil different construction needs, caisson foundations stand out for the value they serve in both dry and underwater environments. This blog will take an in-depth look at different types of caisson foundations.
What is a Caisson Foundation?
A caisson foundation is a strong structure that is built to withstand heavy buildings or bridges. It’s like a big box or tube built on land or in water and then sunk into the ground until it reaches solid soil or rock, to hold up the structure above. It’s used when the ground near the surface isn’t strong enough to hold the building.
Importance of Caisson Foundation
- Used to bear heavy loads, especially for large structures such as bridges, tall buildings, and piers.
- Offers stable layers of soil or rock when the surface soil isn’t strong enough to withstand the overlying structures.
- Crucial for the construction of underwater structures, offshore platforms, and bridges, where regular foundations cannot be constructed.
- The solid base it offers helps in preventing the structure from settling or shifting over time.
- It offers versatile applications due to its adaptability in different environments like underwater, soft soil, or rocky terrain.
Types of Caisson Foundation
Box Caissons
Box caissons are large, rectangular or square boxes made from reinforced concrete or steel. These boxes are sunk to the desired depth and are used for soft, deep soil or underwater environments, to support bridges and offshore structures. They are easy to construct, inspect, and don’t require compressed air.
Excavated Caissons
Excavated caissons are constructed by creating a shaft or tube on the surface and excavating it to the desired depth. This caisson is most commonly used in places with soft and unstable surfaces or in places that require a deep foundation. It is ideal for large-scale industrial projects and marine structures.
Floating Caissons
Floating caissons are big, hollow structures that float on the water’s surface. These caissons are built away from the site and are placed deep into the water. It is primarily used in marine environments for the construction of foundations in deep waters. These foundations hold structures like bridge piers, large marine structures, and offshore platforms.
Open Caissons
Open caissons are open-bottomed structures that are used to dig into the ground as they sink. They allow continuous excavation, which is suitable for deep excavation as the caisson moves down without the need for heavy machinery. They are ideal for areas with waterlogged, soft soils and marine environments.
Pneumatic Caissons
Pneumatic caissons are similar to open caissons, but they involve an air pressure system to prevent water and soil from entering. They are widely used in marine or underwater environments, where open caissons are ineffective due to water pressure. They work in underwater environments and areas with high water tables, for the construction of bridge foundations, tunnels, and underwater constructions.
Compressed Air Caissons
As the name suggests, compressed air caissons use compressed air to remove water and allow workers to safely excavate in waterlogged or underwater areas. They are similar to pneumatic caissons, but higher pressures are used to counter harsh digging conditions. These caissons are effective in waterlogged or deep underwater environments for the construction of underwater foundations, bridge piers, and docks.
Monolithic Caissons
Monolithic caissons are solid structures made of concrete or steel. Unlike other caissons, they do not have joints and are mostly built as a single piece. They are used in places where a strong and solid foundation is crucial and needs to withstand corrosion and wear. These caissons are used for the construction of large and high-load-bearing structures, bridges, and offshore platforms.
How to Choose the Right Type of Caisson Foundation?
Soil and Ground Conditions
If the soil surface is too soft or unstable to support the structure, a pneumatic or open caisson can be used. These caissons help to sink through the unstable layer to reach the solid ground surface for a stable foundation.
In places of rocky or strong soil layers, a box caisson or monolithic caisson can be used. These caissons provide a stable foundation and are easier to install in harder conditions.
Water Table and Underwater Construction
For places with high water tables or if the construction needs to be carried out underwater, a pneumatic caisson or compressed air caisson can be used. These caissons use pressurised air to prevent flooding and make the place safe and secure for excavation.
If the site is near shallow water or waterlogged, an open caisson or floating caisson can be used. These caissons are designed to sink and work in water-clogged environments.
Depth of the Foundation
For shallow foundations, a box or excavated caisson can be sufficient, as they provide adequate stability at moderate depths. If the foundation is too deep into the ground, then floating or monolithic caissons can be used, particularly in watery or unstable soil environments.
Load-Bearing Requirements
For places where heavy load-bearing capacity is crucial, monolithic caissons can be used to provide a strong, solid, and continuous structure. For moderate load-bearing places, box caissons or excavated caissons can be used to provide adequate support.
Project Timeline and Cost
If the project needs to be completed within a tight deadline, floating caisson can be used, as they can be prefabricated and floated to the site. If the budget is a concern, box caissons or excavated caissons can be used, based on the site conditions.
Environmental Conditions
For marine environments and places that are prone to saltwater corrosion, monolithic caissons or box caissons can be used. These caissons are more durable to resist corrosion over time. For urban environments with no underwater challenges, excavated caissons can be more practical.
Conclusion
In summary, caisson foundations are an essential part of construction that requires deep or underwater support. There are numerous types of caisson foundation options that serve different purposes. Soil conditions, water table, load-bearing requirements, and environmental conditions determine the right type. The choice needs to be specific to ensure the stability, durability, and longevity of the structure.
Mithali Konety