Foundation is one among the foremost vital elements of the structure. Foundation is outlined as that a part of the structure that transfers the load from the structure moreover as its own weight over an
outsizes space of soil in such how that the load doesn’t exceed the final word bearing capability of the soil and therefore the settlement of the whole structure remains inside a tolerable limit. Foundation is that the a part of a structure on that the building stands. The physical object on that the muse rests is termed the muse bed.
Why a Foundation is Provided ?
Foundation ought to fulfil the subsequent objectives:
1.Distribute the burden of the structure over an outsized space of soil.
2.Avoid unequal settlement.
3.Prevent the lateral movement of the structure.
4.Increase structural stability.
Why There square measure differing types of Foundation ?
As we all know that there square measure differing types of soil and bearing capability of the soil is completely different for every individual variety of soil. therefore reckoning on the profile, size and cargo of the structure, engineers selected differing types of foundation.
In general, all foundations square measure divided into 2 classes, like SHALLOW FOUNDATIONS and DEEP FOUNDATIONS. The terms Shallow Foundation and Deep Foundation visit the depth of the soil at that the muse is placed. Generally, if the breadth of the muse is bigger than the depth of the muse it’s labelled as “Shallow Foundation” and if the breadth of the muse is smaller than the depth of the muse it’s referred to as as “Deep Foundation.”
Several types of shallow foundations are listed below:
1. Isolated Spread Footing
This is the most common type of foundation and most economical foundation system. They are generally used for ordinary buildings up to five stories. Isolated footing consists of footing at the column base. The footing directly transfers the loads form the column to the earth surface. The footings having different shape such as rectangular, square or circular in shape. The size of the footing can be calculated by dividing the total load at the column base by the allowable bearing capacity of the soil.
Isolated Spread Footing is economical when the load of the structure is comparatively low, spacing of column is very far from each other and the maximum Bearing capacity of the soil at a shallow depth.
2. Wall Footing or Strip footing
This type of footing is utilise to distribute loads of load-bearing structural walls to the ground. Wall foundation constructed along the direction of the wall. The width of the wall foundation is generally 2-3 times of the width of the wall.The wall footing is continuous slab act as a strip along the length of the wall. Stone, brick, reinforced concrete is used for the construction of wall foundations.
Wall footing is very economical when the load need to be transmitted are in small magnitude and the footing is placed on dense sand and gravels.
The combined footing is same as to the isolated footing bur the difference is the more than one column are attached in one footing. When the columns of the structure are closely placed and the bearing capacity of the soil is low and their footing overlap such time combined footing is provided. Rectangular trapezoidal are the various types of the combine footing.
4. Cantilever or Strap Footing
In Strap footing the footings under the columns are built individually and link column by strap beam. Generally, when the edge of the footing cannot be extended beyond the property line the exterior footing is connected by beam with internal footing.
5. Raft or Mat Foundation
Raft or Mat foundations are implemented where other shallow foundation or pile foundation is not suitable. It is also suggested in situations where the bearing capacity of the soil is very poor and the load of the structure is distributed over a big area or structure is constantly subjected to jerks.
Raft foundation consists of a reinforced concrete slab ,T-beam slab placed over the entire area of the structure. In this type of foundation the overall basement floor slab work as the foundation. The total load of the structure is distributed evenly over the entire area of the structure.
Raft foundations are economic when the soil is weak and the load has to be spread over a big area, also the structure includes a basement and columns are closely placed.but due to this differential settlement are prevented.
Written By : Parag Kamlakar Pal
B.E (Civil Engineering), NICMAR (Advance construction management)