The foundation is the most important part of any structure because if we make a small mistake in foundation design it will reflect huge impact.
Function of Foundation
The foundation has received the all loads like dead load, live load, seismic load, etc., which is distributed to column & it transfer to the ground. The entire pressure of the structure should not greater than the safe bearing capacity of soil (SBC).
We have to consider the following factor while designing the foundation
The foundation has classified two major types Shallow Foundation & Deep Foundation.
The types of shallow foundation classified as below
1. Isolated footing 2. Combined footing 3. Strip footing
When a depth of foundation is less than or equal to the breadth of the foundation is called Shallow foundation. The shallow foundation has classified into three main categories.
Isolate – Alone
If each column has an individual footing is called Isolated footing. Most of the small size building has constructed by this type of foundation because it is simple & economical.
Generally, the isolated footing is placed when the soil has the low safe bearing capacity. The common shape of the footings is square, rectangular & circular section.
There is no big difference between the isolated & combined footing. When more than one columns are placed at a distance below 2 m then it was designed as a combined footing. The combined footings are having a shape Rectangle or trapezoidal.
The Strip footing have slight differ compares to other types of shallow foundation. This footing has placed where the soil having good bearing capacity available at below 3m from the ground level.
Another name of Strip footing is Wall footing because the width of the footing is 3 times greater than the depth of footing.
There are two types of Strip footing mentioned below
1. Simple Footing 2.Stepped Footing
If the structure shall carry a small amount of load then the footing was designed as simple footing.
Mostly stepped footing is designed when the ground is slope unless if we provide for the normal ground level it becomes uneconomical.
Raft & Mat foundations both are same. When the soil bearing capacity is low but the same time the large structure has planned to construct in that area then we have to recommend the Raft foundation (Depth above 3m).
If the selected construction area is very large & type of soil is different from one place to another place. So we excavate the entire area fully & placing Raft foundation.
You Shall ask why we are not using Pile foundation instead of Raft foundation!. because economically it was too high.
In mat foundation, the column has placed at a minimal distance to distribute the load to ground.
Once again remind you, as above said based on the soil bearing capacity the design will differ. If the bearing capacity is good & the structure was small size then we recommend isolated footing.
We must interpret about the one more type of footing that is Strap footing.
Mostly these type of footing has placed when the construction area is not having much space to give proper foundation. So that in this condition, the Strap footing was provided & the column shall be designed as an eccentrically loaded column.
When the depth of foundation is greater than its width, it is called Deep Foundation. When the depth is greater than 6m then design recommends the deep foundation. Mostly pile foundations are called deep foundation.
The main purpose why we use the pile foundation! When the soil has the low bearing capacity or water logged area (Loose soil). Mostly pile foundation have designed when the soil has a low bearing capacity, highly water log area at the same time the foundation to accommodate the large load.
Types of Depp Pile of Foundation.
- Bearing piles 2. Friction pile
End Bearing Pile
End bearing pile shall use when the hard soil (Rock) strata found at a reasonable depth not less than 40m. The End bearing pile simply acts like Column, the entire load of the structure has distributed to the hard surface area. Piles are driven into the soft soil & it will stop when it reaches the hard surface area.
There is no major difference between the bearing & Friction pile. Friction pile has used at the depth greater than 40m. The same methodology has used to execute the pile work but the friction pile has transfer the entire load of the structure to soil through by Friction between the Surrounded Soil & pile. The load was transferred downward & laterally to the soil.
We just see a glance of pile foundation. In the upcoming post, we shall discuss briefly pile foundation.