Caisson Foundation
- The foundation system of and the soils beneath the building prevent the complex from moving vertically.
- When a load is placed on soil, most soils settle. This creates a problem when the building settles but the utilities do not. Even more critical than settlement is differential settlement.
- This occurs when parts of your building settle at different rates, resulting in cracks, some of which may affect the structural integrity of the building. Conversely, in some rare instances soils may swell, pushing your building upwards and resulting in similar problems.
- Therefore, the foundation system must work in tandem with the soils to support the building.
WHAT IS CAISSONS?
- It’s a prefabricated hollow box or cylinder
- It is sunk into the ground to some desired depth and then filled with concrete thus forming a foundation.
- Most often used in the construction of bridge piers & other structures that require foundation beneath rivers & other bodies of water
- This is because caissons can be floated to the job site and sunk into place
- Basically it is similar in form to pile foundation but installed using different way
- used when soil of adequate bearing strength is found below surface layers of weak materials such as fill or peat
- It’s a form of deep foundation which are
- constructed above ground level, then sunk to the required level by excavating or dredging material from within the caisson
- A caisson foundation consists of concrete columns constructed in cylindrical shafts excavated under the proposed structural column locations
- Caissons are drilled to bedrock or deep into the underlying strata if ageotech eng. find the soil suitable to carry the building load
- It’s created by auguring a deep hole in the ground
- Then, 2 or more ‘stick’ reinforcing bar are inserted into and run the full length of the hole and the concrete is poured into the caisson hole.
- The caisson foundations carry the building loads at their lower ends, which are often bell-shaped.
TYPES OF CAISSONS
- Box Caissons
- Excavated Caissons
- Floating Caissons
- Open Caissons
- Pneumatic Caissons
- Sheeted Caissons
ADVANTAGES & DISADVANTAGES
ADVANTAGES
- Economics
- Minimizes pile cap needs
- Slightly less noise and reduced vibrations
- Easily adaptable to varying site conditions
- High axial and lateral loading capacity
DISADVANTAGES
- Extremely sensitive to construction procedures
- Not good for contaminated sites
- Lack of construction expertise
- Lack of Qualified Inspectors
Caisson Foundations
- A drilled pier is a deep foundation system that is constructed by placingfresh concrete and reinforcing steel into a drilled shaft.
- The shaft is constructed by rotary methods using either a self-contained drill unit or a crane mounted drill unit. The hole is advanced through soil or rock to the desired bearing stratum. Temporary or permanent steel casings may be used to maintain the sides of the drilled excavation if caving soils or water infiltration becomes a problem.
- Drilled shafts can be used to sustain high axial and lateral loads. Typical shaft diameters range from 18 to 144 inches.