Caisson Foundation & Its Types in Construction Process
Caisson foundation is a deep foundation form build above ground level, it submerged to the required level by excavating or dredging material within the caisson.
It often uses in the bridge piers construction and other foundation structures under rivers like other water bodies.
Introduction to Caisson Foundation
The term Caisson derives from the French word Caisse means box. It looks like a box-like structure, round or rectangular, that can sink on the surface of both land and water at some desired depth. It satisfies the purpose of placing the foundation in the correct position underwater. Technically speaking, Caissons can define as water-tight boxes which act as a substructure in the main construction.
Caisson Foundation Requirement
1. Soil contains massive boulders that obstruct the penetration of the piles.
2. A humongous substructure is required underneath the rear bed to offer resistance to the forces that might be dangerous due to floating objects, notch, etc.
3. The foundation subject to a vast lateral load.
4. The depth of water level in river and sea is high.
5. There are river forces involved in load compositions.
6. The groundwater levels are aggressive.
Types of Caisson Foundation
Open Caisson Foundation: Open caisson is unwrap at the top and bottom. It is vacant chambers and cutting-edge at the bottom of the caisson. The shafts sink into place by eliminating soil from within the Shaft or chamber until the bearing reaches the echelon. Typically, an open caisson penetrates it through a dry or wet construction area or an artificial island.
A synthetic sand island formation elevates the ground surface above the water level. Thus a dry area is obtained to submerge the caisson, the sand island dimensions should be sufficient to give a working space around the caisson. In this case, it is impossible to immerse the caisson in the dry areas, built-in spillage, or barge then transported to its final location by floating.
Pneumatic Caisson Foundation: Pneumatic caisson requires when the soil surrounded cannot be excavated satisfactorily. It also works in a steady water flow or tight obstructions occurring during submergence.
Pneumatic caissons are open at the bottom & closed at the top. At the bottom of the pneumatic caisson is a working chamber that maintains compressed air for the stress required to prevent the entry of water and dust into the caisson.
Floating Caisson Foundation: Floating caissons are boxes with large holes open at the top and closed at the bottom. This caisson floats at the base, fills the site with sand, ballast, dry concrete, and gravel. A floating caisson does not infiltrate the soil like the open and pneumatic caisson & remains on the flat bearing surface.
The load-carrying capacity exposes as resultant aspect friction at the bottom resistance. The caisson sinks to its final position. It fills with sand or gravel. A solid cap is created on top to tolerate the structural load to avert rip-off below a rip-tear is pouring across the base. Normally, these caissons are of R.C.C or metal. The Caisson formation may be round, square, rectangular, or elliptical.
Box Caisson Foundation: Box caisson includes containers on four side bottom, and top of these boxes are open & the concrete ground builds at the bottom. The finished box caissons place in the original location to the pre-prepared board position. Once a suitable location decides, the entire void fills with concrete. Box caissons are cost-effective when it is impossible to assemble on site.
Excavated Caisson Foundation: The excavated space positions this caisson, generally cylindrical and then filled with concrete.
The following steps can adopt to construct the caisson foundation as follows:
a) We should first determine the place for the establishment of the caisson. It is 3.7 meters pre-cast.
b) With the help of the towboat, the caisson is taken to the construction site, and anchorage cables tie to the caisson.
c) Concrete uses to make the slips with the area becomes heavy and submerged in water.
d) Anchorage cables are used to hold caissons in place.
e) When the caisson touches the bottom of the river, the anchorage cables remove.
f) Finally, the cap inserts.
Pros of Caisson Foundation
a) Caisson is more economical.
b) The pile reduces the need for the cap.
c) It makes less noise and vibration during construction.
d) They can transfer to different site conditions.
e) It has High axial and lateral loading capacity.
Cons of Caisson Foundation
a) It is highly sensitive to manufacturing processes.
b) They are not good at polluted places.
c) Lack of building experience.
d) Lack of skilled laborers.
Caisson foundation gives a different means to achieve satisfactory installation at intermediate depths to critical depths in both ground and water surroundings.