What are the type of foundation? And how to choose it.

Foundation is the low part of the structure which transmits the load of the structure to the ground. The foundation is a buried structure and we cannot see it directly as superstructure. This fact creates bias-ness in designer towards the superstructure which foundation remain given less importance.

So, before designing the foundation it is necessary to know the factors which affect the foundation. Also, it is necessary to know the basic requirements of foundations.

1. Types of foundation

As per the depth of the base of foundation level, foundations are divided into two types:

A) Shallow foundation

In Shallow foundations, the ratio of the width of the foundation is greater than its depth. Or in other words, the ratio of depth/breadth is less than unity. When the structure is small and bearing capacity can withstand it, the shallow foundation is recommended. The cost of shallow foundation is less than deep foundation.

B) Deep foundation

In Deep foundations, the ratio of width to depth of foundation is greater than unity. Usually in loose soil and when the bearing capacity of a soil is not suitable to built structure on it, deep foundations are recommended.

Know More about: Types of Deep Foundation

2. Engineering process of foundation design

These steps are followed in the design process of the foundation.

1. First of all, field visits and site investigations are done.
2. Detail about the site is collected and necessary soil test at the field is done and samples for a laboratory test are taken.
3. At the laboratory, the sample is properly tested and a detailed analysis of the nature of soil with idealize profile and problem is listed.
4. After finding out the problems, a detailed analysis is done and the solution is to find out.
5. If it was okay to construct on such a site then the design process is started.
6. At last, the construction process is started.

3. Factors affecting the selection of foundation

The following factors affect the selection of the foundation.

1. The function of the structure.
2. The load the foundation carries.
3. The sub-surface conditions.
4. Cost of foundation in comparison to the cost of super-structure.
5. Construct-ability
6. Service life
7. Needs of client or owner
8. Type of super-structure
9. Environmental considerations
10. Margin of safety
11. Risk level

4. Basic requirements of the foundation

1. The primary requirement of a foundation is to maintain the stability of the superstructure without impairing its intended use. In both deep and shallow foundations, the following requirements are necessary.
2. The depth of the foundation must be adequate. The foundation must be properly located with respect to any future influence, which could adversely affect its performance. It involves many different factors, some of which cannot be evaluated analytically and must be selected by proper engineering judgment.
3. The foundation must be stable or it should not overstress the supporting soil. This requirement is specific. It is analogous to the need that a beam within the construction should be safe against breaking under its own load.
4. The foundation should not undergo excessive settlement or it should not damage the structure or impair its intended use. This requirement is both specific and nebulous. This is analogous to the requirement that a beam in superstructure must not deflect more than a specified value which cannot be ascertained accurately.
5. The foundation must not over-stress the underlying soft soils.

5. Some Common Problems With Foundation

Settlement of foundation occurs due to:

1. Consolidation of soil particles.
2. The heaving of the soil.
3. Reduction of moisture content (due to drying evaporation).
4. Earth movement (mining operations, earthquakes, etc).

Effects of unequal settlements:

Distortion of the structure.
Failure of the structure.

Prevention of unequal settlement

1. Proper soil investigation.
2. Proper foundation design.

Causes of foundation settlement are:

1. Unequal settlement of sub-soil.
2. Nearby building construction.
3. The horizontal movement of soil adjoining the structure.
4. Unequal load distribution.
5. Lateral pressure tending to overturn the structure.

Also Read: Excavation of Earthwork In the Foundation