Foundation is the structural component of a building that safely transfers loads from the wall or columns to the ground below. It is a part of the substructure or a lower part of a structure.
When foundation of houses or buildings is well built, structures may last for long. To achieve the long service life of a constructed structure, it is essential to design the related foundation as per the standard codes of design.
Foundation should also be safe against the effect of sliding and overturning. It is important to build it safe against the risk of settlement or differential settlement. To protect against these unwanted probabilities, a foundation should meet some basic requirements. To know the basic criteria, read the requirements of the foundation system here.
The stability of a good foundation system depends on multiple factors. Hence, selection of the right foundation system is very important.
Generally, foundation systems are of two types. It can be either a shallow foundation or a deep foundation. As the name suggest, a shallow foundation has a lower depth as compared to a deep foundation.
The shallow and deep foundation system includes various types of foundation to add stability, balance, and endurance to a structure. It is not that difficult to select the right foundation system or right footing for your house, provided you know the factors actively or passively responsible for the quality and stability of a specific foundation. If you want to learn about the best foundation system and the relation of these factors with the stability feature, read here.
Factors Affecting the Selection of Foundation
Choices of the foundation will depend on manifold factors. Apart from the factors discussed below, it also depends on the closeness of the trees, drain and stability of slope, etc.
01. Utility of the Building
We use buildings for different purposes i.e. industrial or residential or institutional purpose. If the building is of more importance like schools or hospitals, it needs better and long-lasting foundation system support.
02. Lifespan of the Structure
Building a strong foundation leads to longer life span of a building. If you want to expand the service life of the foundation, you need to construct a building with a solid foundation. Proper planning and use of right material can lead to the longer life span of a building.
03. Number of Floors: Height of the Building
Height of the building is one of the major criteria for selecting the right foundation. Furthermore, if the building has more number of floor, you have to construct a stronger foundation.
04. Loads from the Structure
Gravity and lateral loads act on a house or on a building. It is an important and remarkable consideration for the final selection of the construction. Based on the location of the houses or buildings, a combination of dead loads and live loads are considered. Other loads like wind loads, snow loads, earthquake loads, etc. need to be also considered.
05. Materials of Construction
Number of trending construction materials are available nowadays. Selection of material such as bricks, stone, steel, concrete, etc. for construction also affect the selection of foundation.
06. Understanding the Soil Type is Important
There are various types of soils such as sandy soil, loose soil, clayey soil or expansive soils, etc. The soil nearer to the soil surface is called topsoil and next 3.00 m depth from the surface is called as subsoil. These subsoils are used for back filling the foundation of buildings.
Each soil has different nature, and hence, different soil bearing capacity (SBC).
As per the engineering manual “Engineering and Design Bearing Capacity of Soils” by the Department of the Army, U.S. Army Corps of Engineers, Washington, DC (1992), the Bearing capacity is the ability of soil to safely carry the pressure placed on the soil from any engineered structure without undergoing a shear failure with accompanying large settlements.
Soil Bearing Capacity (SBC) affects the selection of foundation. Lower SBC soil needs stronger foundation as compared to the soil with higher SBC.
Furthermore, when the structure exerts the load to the soil through the foundation, the upcoming load tends to consolidate the soil. It results into the settlement of the concerned foundation system. The major cause of foundation cracks in a construction is due to the settlement of the house or structure. Eventually the foundation may fail and this can be the reason of collapse of a constructed structure. To know about it in detail, kindly read various reasons of building collapse.
07. Water Table Level
A foundation system depends on the depth of the water table. A foundation should rest either on fully dry soil or on fully wet soil. Avoid a soil layer that dries and wet alternately with change in the seasons. To know more, read how to do foundation in water.
08. Building Location
Natural disasters like the earthquake, cyclone, flood, volcano, etc. often exert destructive impact on the foundation of a structure. That is why, the effects of these inevitable natural calamities are to be counted at the time of the selection of a foundation.
Furthermore, we must consider local zones while designing the foundation like local climate, rainfall percentage, soil type, frequency of having storm, seismic mapping etc. If there is a history of natural disaster or extreme weather, the selection of the foundation should be made based on the past data of natural calamity and climactic variance in that locality.
09. Adjoining Structure/Water Bodies/Slopes
In building a construction, selection of foundation also depends on the neighboring structures. If the foundations of an adjoining structure are very near to the target foundation, it may affect the choice as the safety of adjoining structure is of paramount importance. Furthermore, if the adjoining structure is a high-rise or an old property or is built with lesser/compromised depth of foundation, the selection often becomes challenging.
Also, the factors like proximity to a river, lake, or any other water body or closeness to a natural drain or close vicinity to a slope should be taken in counting. If anything, similar is found, it needs thorough investigation and sound engineering judgment to pacify the adverse effect if any. In such case, experts should be final decision taker about the best foundation for the building.
10. Choosing the Right Kind of Construction
There are different varieties of foundations and every option has it pros and cons. You must know at least the outline details of all the varieties in order to decide the best for a foundation.
At a glance, followings are the options of foundation in hand majorly used for constructing a house or building.
- Wall footings
- Isolated footings
- Combined footings
- Strip footings
- Raft footings
Selection of foundation should be based on the technical suitability and related financial budget also.
As stated in the thesis cum research paper “Building Construction” by ‘P. C. Varghese’, the average percentage cost of the civil work of foundation system for residential building is normally 10 to 15%. Hence, cost of the construction of a foundation is quite important while you choose the types of foundation system for the house. However, when you spend more on interiors, it is a bad idea to cut cost in foundation.
Thus, it can safely be said that selection of the foundation is not a matter of personal discretion but it is a logical proposition based on data of soil analysis, evaluation of the water table level, detailed knowledge of the concerned locality, its climate, etc. Likewise, detailed data about the depth of soil layers and the safe bearing capacity of the soil at different levels is also a matter of concern. Only based on these data, you can select the right type of foundation for the best endurance and safety.
There are 10 major factors that generally create active impact on the selection of a foundation for a stable and planned construction be it is a house or a commercial property. Without knowing these 10 factors, one should not select the foundation for any structure. The right choice of foundation type is one of the most important judgments that a structural engineer has to work out in the gamut of his job responsibility. Summing up, remember never economize on foundation costs. It is the worst place to control your cost. Hence never do it, never.