What Is Caisson Foundation?
Caisson Foundation is a watertight structure that is generally made up of timber, steel, and reinforced cement concrete (R.C.C) and constructed in connection with the excavation for the foundation of piers, bridges, and dock structures etc.
Basically, the word Caisson means a box-type structure. It is a large diameter foundation which is generally adopted in the underwater Construction.
It is a Prismatic Hollow box for the cylinder which is constructed on the ground and then sunk into the ground at the desired depth and filled with the concrete to form a foundation for the Structure. Construction of Caisson is a type of well foundation. Caisson foundation is used for the Construction of a Deep foundation.
Caisson Foundation is widely used in the construction of piers of the bridges and the foundations of structures which are constructed in the rivers or water bodies. The main functions of caissons are soil or water retention and transfer of vertical and horizontal loads into the subsoil strata.
Caisson Foundation
Caisson foundations, also known as pier foundations, are prefabricated hollow substructures designed to be constructed on or near the surface of the ground, sunk to the desired depth and then filled with concrete, thus ultimately becoming an integral part of the permanent structure.
Advantages of Caissons Foundation
- Excavation and the process of concreting can be done in dry conditions.
- Caissons are good in the lateral as well as axial loading capacity.
- Caisson is highly adaptable in different site conditions.
- Caissons are economical as compared to traditional foundation.
- Caisson can be inserted at any place.
- It is strong enough to withstand the moments and loads applied to the structure.
- Caisson does not require pile caps, because it is filled with concrete.
- Caissons have a large cross-sectional area which helps to resist the scouring effect.
- Caissons can be extended up to the large depths in the ground.
Disadvantages of Caisson Foundation
- The Inspection and cleaning at the bottom of the Caisson are difficult.
- There is a lack of skilled workers which are required for the construction of the Caisson Foundation.
- Caissons can not be construed in the contaminated sites.
- Caissons are required to be constructed under the supervision of the Experts.
- There may be a risk to the workers to get affected by the caisson diseases. So the proper health control is essential.
- The limit for the depth of the penetration of the Caisson is up to 35 m.
Application of Caisson Foundation in Civil Engineering
- It is used in the construction of piers of the bridges in the water bodies.
- Caisson is also used in the construction of large and Multi-Floor Buildings.
- Caissons provide a platform for the installation of machineries and pumps below the ground level.
- Pneumatic Caissons are used in the construction of railway bridges.
- Caissons are also used to provide access to the shaft and tunnels.
Types of Caisson Foundation
The Shape and the size of the Caisson is depended upon the structure for which it is constructed. Caissons are classified mainly into three types.
- Open Caisson.
- Box Caisson.
- Pneumatic Caisson.
1. Open Caisson
Open Caisson is a box-type hollow structure which is generally open at both top and bottom side. Open Caisson is suitable for the sandy soils and the soil having soft strata where a solid or firm stratum is not available.
Open Caisson is constructed in reinforced cement concrete (R.C.C) and the middle portion filled with sand or gravel and the lower portion is filled with the concrete which acts as a concrete plug.
The Construction of the Open caisson is generally preferred in the dry condition or dewatered area. If it is not possible on the site to construct the Caisson in the dry conditions then it is constructed in the barges or slipways. According to the shape of the Open Caisson are classified as
- Single Wall Open Caisson
- Cylindrical Open Caisson
- Open Caissons with Dredging Wells.
2. Box Caisson
The Box Caisson is the same as the open Caisson. The only difference between open and box Caisson is that box Caisson has its bottom side closed. It is made up of timber, steel, and reinforced cement concrete ( R.C.C). Box type of Caisson foundation is generally used where the bearing stratum of the soil is available at the shallow depth.
3. Pneumatic Caisson
Pneumatic Caisson is open at the bottom side and closes at the top side. Pneumatic caisson is specially used at the place where it is not possible to construct well.
It is suitable where the depth of water is more than 12 m. In the construction process of the pneumatic Caisson, the compressed air is used to remove water from the working chamber and the foundation work is carried out in the dry condition.
The process of the Construction of the pneumatic Caisson is the same as the open Caisson. The Quality Control in the Pneumatic Caisson is good because the work is done in the dry conditions. Pneumatic Caissons are more expensive as compared to the Open Caisson.
Construction Method of Caisson Foundation
There are various methods by which Caissons are installed into the ground.
Prefabrication of Caisson
- Firstly, the caissons are generally prefabricated near the Construction site or at any other suitable location.
- After prefabrication of the Caissons, they are tested for water tightness.
- In the tests, the Caissons are check for any leakages and, if found they are repaired immediately.
Transportation of the Caisson
- Then the Caissons are transported to the required location.
- The transportation of the Caisson should be done by following all precautionary measures.
Positioning and Immersion of Caissons
- It is very important that Caisson should be properly positioned at the desired place.
- The final positioning of a caisson is achieved with the help of tug boats or with cables from floating equipment and anchors or dead-man beds.
- When the caisson is ready, the soil is dug from the work chamber which causes the caisson to subside into the ground.
- Traditionally the excavation is done by the hand but nowadays sand pumps and other machinery are used for the excavation.
- The excavated soil is removed with the help of a hydraulic transport system.
- The Caisson is subsided under its own weight.
- When the caisson has reached the desired depth, then the work chamber is completely filled with Concrete. This prevents further sinking of the Caisson.
Ballasting
- After the immersion of the Caisson, they are ballasted.
- The main function of the dump of rubble at the side of the caisson is to prevent it to slide away and helps to maintain maximum stability.
Frequently asked questions (FAQ) that could be included in your article about caisson foundations:
What is a caisson foundation?
A caisson foundation is a watertight structure typically made of timber, steel, or reinforced concrete. It’s used in underwater construction to create a sturdy base for bridges, piers, and other structures.
What are the advantages of caisson foundations?
Caisson foundations allow for dry excavation and concreting, making them suitable for various site conditions. They offer excellent lateral and axial load capacity, are adaptable, economical compared to traditional foundations, and can be placed almost anywhere.
What are the main types of caisson foundations?
Caisson foundations are classified into open caissons, box caissons, and pneumatic caissons. Each type has specific applications based on soil conditions and depth of water.
How are caisson foundations constructed?
Caissons are typically prefabricated, tested for watertightness, transported to the site, and positioned using tugboats or cables. They are then submerged into the ground, filled with concrete, and ballasted to ensure stability.
What are the challenges or disadvantages of using caisson foundations?
Challenges include difficulty in inspection and cleaning, the need for skilled labor, limitations in contaminated sites, and risks associated with caisson-related health issues. Depth penetration is also limited to around 35 meters.
Where are caisson foundations commonly used in civil engineering?
Caisson foundations are essential for constructing bridge piers over water bodies, large multi-floor buildings, and for providing underground platforms for machinery and pumps.
What are some key differences between open, box, and pneumatic caissons?
Open caissons are open at both ends, suitable for sandy or soft soil conditions. Box caissons have a closed bottom and are used where shallow bearing strata are present. Pneumatic caissons are sealed at the top and open at the bottom, used in deeper water where dry conditions are needed for construction.
What are the safety measures involved in constructing pneumatic caissons?
Pneumatic caisson construction involves using compressed air to maintain a dry working environment underwater. Strict safety protocols are essential to prevent decompression sickness and ensure worker safety.
How do caisson foundations contribute to environmental sustainability?
Caisson foundations can minimize environmental impact by reducing disturbance to surrounding soil and water during construction, compared to traditional methods that may require extensive dewatering and excavation.
What future trends are influencing the design and use of caisson foundations?
Advances in materials technology, construction methods, and environmental regulations are influencing the development of more efficient and sustainable caisson foundation designs for future infrastructure projects.
