We have explained the different types of deep foundation in detail below. But, before this let us see some important terms regarding the foundation.
Foundation is a structure that acts as a medium to safely transfer all the loads from the superstructure to underlying load-bearing strata. It is the lowermost part of the structure. Foundation can be below or above the ground.
The basic requirements of foundation
- To safely transfer a load of superstructure to the load-bearing strata.
- To provide leveled working surface to the above superstructure.
- To ensure the stability of the Structure.
- To distribute a load of superstructure uniformly in large areas.
For any structure type and size of foundation depends upon the following factors.
- Load from the Superstructure.
- The life span of the Structure.
- Geotechnical condition of the underlying soil.
- Ground Water Table
- Soil Profile
- Characteristics of soil
- Importance Factor of the Structure.
- Type of Material being used for the foundation.
- Time and Cost available.
- Constructability of the foundation
Classification of the Foundation
On the basis of Material
On the basis of depth of foundation
1) Shallow Foundation
- Wall Foundation (Strip Foundation)
- Individual foundation (Spread Foundation)
- Strap Foundation (Cantilever Foundation
- Combined Foundation
- Mat Foundation
2) Deep Foundation
- Pile foundation
- Well Foundation
What is Deep Foundation?
When the bearing capacity of soil near the surface is not enough to resist the estimated load from the structure then the depth of the foundation needs to be increased until hard strata are encountered. Therefore, in such cases, deep foundations are constructed. In deep Foundation ratio of depth to width of the foundation is greater than 1.
Deep foundation transfers load in gradually in the vertical direction to the depth of the foundation, unlike shallow foundation which transfers load in a lateral manner.
Types of deep foundation
1) Pile Foundation
Piles are the slender members driven in the soil to transfer loads of superstructure in load-bearing strata. Piles are basically used in groups. Piles are used to transfer load through poor soil or water to suitable strata.
It can also be used as a compaction pile to increase the bearing capacity of the soil and resist lateral forces. Piles also serve as tension pile to resist uplift load or to anchor the structure.
Piles are flexible structure in a sense that its shape and sizes, the material used, mode of Construction, load transfer, mode of installation can be altered according to the requirements of the site.
Advantages of the Pile Foundation
- Speedy Work is possible
- Reduction in excavation, since they are driven into the soil.
- Pile installation is not affected by the groundwater table
2) Well Foundation
These are massive structures in a form of well. The outer wall is pre-casted and sunken in the site is made up of RCC, wood, steel, and sand is filled inside. The Shapes of good foundation need not be mandatorily circular, Double D, Dumbbell twin octagonal, rectangular shape are also used.
They are best suited where heavy uplift forces are encountered like transmission lines and below rivers. The main components of a good foundation are wall steining, Top plug, Bottom plug, well cap, dredge hole, Cutting edge, and Curb. They are also known as caissons.
Well Foundation can be of three types:
- Open type well
- Box Well
- Pneumatic caissons
Advantages of the well Foundation
- Due to its large section and rigidity, it can take large lateral loads moments and can resist scouring better.
- Well foundation construction does not affect the adjacent structure, sinking components of well foundation are sunken than cast.
- The depth of the foundation can be determined as the sinking progress. Well Foundation also acts as a borehole to inspect soil type.
3) Piers Foundation
Piers are the cylindrical column with a large diameter used as a deep foundation. Piers are similar to the piles unlike piers have excessively large diameter than piles. Piers are usually made of masonry or RCC. When the hard rock is available at depth of about 5 m piers are preferred. Piers can be cast in situ and drilled.
Advantages of Pier foundation
- Large excavation is not required which results in economic construction.
- Bearing capacity can be increased by reaming the base of the pier.
- Piers have flexible sizes and designs, which can be used to add aesthetic value to the structure.
So, these are the different types of deep foundation. Now, let us see suitable condition to use deep foundation.
Where to used Deep Foundation?
Following are the areas where deep foundations are feasible
- To support Bridge like structure.
- To support Flyovers
- When the soil near the surface does not have sufficient bearing capacity to resist the structure.
- For the high-rise structures and skyscrapers.
- For underwater construction and construction over water.
Advantages of Deep Foundation
- Constructions are possible in weak soil or water.
- High-rise buildings can be constructed with the use of deep foundation.
- There will be no design constraints for the architects as a deep foundation will facilitate in completion of complex structures.
- There will be proper land use since the marshy land and wetlands also could be converted into commercial use.
Disadvantages of Deep Foundation
- They are a costly structure.
- Construction of a deep foundation might have a negative effect on the nearby structures in the vicinity of it.
- Proper design, supervision, and construction by skilled resources are needed.
- There is a high risk in the construction of a deep foundation.
Different between pile, pier and Caisson
I hope this article on “Types of deep foundation” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Rukshana Shrestha