Pier Foundation [what when types how]
Pier foundation is types of foundations that are constructed from small scale to larger in scale when compared to the other types of foundations.
As the name implies, a pier foundation is a combination of large diameter piers constructed to support the structure to transfer its loads to the ground.
Classification of the foundation is made based on the method of construction or considering the nature of the structure.
Types of Pier Foundation
There are three main types of pier foundations.
- Masonry Piers
- Concrete Piers
- Drilled Caissons
Masonry Piers
Masonry piers are constructed when there are hard soil layers at the shallower depths. The depth of the masonry pier could be continued up to 4-5m.
When the depth to the hard soil layer increases, it is very difficult to construct the foundation of this nature.
The masonry pier foundation could be constructed in different shapes such as circular, rectangular, hexagonal, etc.
There are many old structures constructed as pier foundations in old-time even where the concrete was not invented. Further, the construction of pier foundations was common earlier to 1950.
Concrete Piers
Concrete piers were also constructed to serve the same purpose as masonry pier foundations.
The size or the diameter of the concrete pier is comparatively smaller when compared to the masonry pier due to its high load-bearing capacity.
Mostly the concrete piers are in circular, square, or rectangular shapes due to the difficulties in constructing other shapes.
There are different types of pier foundations.
- Structure directly supporting on pier foundation rested on the hard soil layer. Piers constructed at regular spacing could be observed in these types of foundation systems.
- Structure supported on the combination of piers. That is piers rest on the hard soil or rock connected by the bases slab and start another set of piers based on the supporting requirement of superstructures.
Drilled Caisson
Drilled caisson are cylindrical shape foundations that are constructed from concrete. The intention is to use the concrete or caisson types of foundation to carry higher axial loads applied from the superstructures.
Drilled caissons are constructed up to the deeper depth when compared to the masonry/concrete pier foundations. Further, excavation for these types of foundations could be done with mechanical means.
Mainly there are three types of foundations.
- Drilled caissons with enlarged bottom constructed from concrete
- Concrete caissons are constructed by filling concrete into the steel pipe
- Concrete caissons with concrete and steel core in the steel pipe
The following figure indicates the three main types of concrete caisson foundation in addition to the masonry pier foundation.
Pier Foundation Design and Construction
- Types of material sued for the construction
- Brick
- Concrete
- Timber
- Steel as caisson
- Shapes of Pier foundation
- Circular
- Rectangular
- Square
- Other shapes such as helical shapes found in old structures
- Construction of Reinforced Concrete Piers
Reinforced concrete piers are constructed where the applied axial loads are comparatively higher. Provided reinforcement increases the axial capacity as well as the bending capacity.
Therefore, not like masonry or concrete pier foundation, reinforced concrete piers have higher structural capacity.
- When and where to construct Pier Foundation
When there are adequately strong hard soil strata or bedrock is closed, these types of foundations can be used for the construction.
Depending on the nature of the structure, the type of foundation could be selected. For example, for structures having low weight, simpler foundations like timber piers could be used. When with the increase of the load, concrete or reinforced concrete pipes could be constructed.
In addition, when the structure is constructed on sloping ground, a pier foundation could be more suitable as they do not require are area to cover like pad footings.
Advantages of Pier Foundation
- Required less skilled labor for most types of foundations
- Less time-consuming when compared to the other types of foundations.
- Pires can be used to build structures above the ground and there are many added advantages like running the building services in this gap.
- There are no vibrations like driven pile foundation
