In this article we will discuss what factors need to be considered when choosing the type of foundation. Choosing the type of foundation is not based on a single factor. Let's discuss how to determine the type of foundation based on the key factors discussed below.
Foundations can be divided into shallow foundations and deep foundations.
Shallow foundations
Foundations built at shallow depths fall into this category. The following list of foundations could be considered.
- Individual foundations
- Combined foundations
- Slab foundations
- Strip foundations
Deep foundations
Deeper foundations fall into this category.
- Molded-in-place plate files
- Driven piles (prefabricated piles)
- Micropiles
The selection of each type of foundation is based on the following factors.
- Significance of the building
- Buoyancy of the structure
- Superstructure loads
- Soil type
- Adjacent structures
- Available foundation types
- construction costs
Significance of the building
The importance of the building is taken into account when choosing the type of foundation. For structures that are not as important or do not need to last as long, foundation design may be less demanding.
For example, when considering a temporary structure, we may disregard foundation settlement. The highest setting may be allowed.
Furthermore, a structure constructed to protect banners/poles should not be designed to limit settlement like a building. The choice of the type of foundation depends on these factors and their importance.
Life of the structure
When choosing the type of foundation, the planned service life of the structure is of great importance.
| Design work life category | Shaping professional life | Example structure |
| 1 | <10 | Temporary buildings |
| two | 10 to 25 | Interchangeable construction parts, portal supports, bearings |
| 3 | 15-30 | Agricultural and similar structures |
| 4 | 50 | Building structures and other similar structures |
| 5 | 100 | Monumental buildings, bridges and other engineering structures |
| 6 | > 100 | Special constructions |
Eurocode 1 contains the above table for specifying structural classes. There are six structural classes based on the designed service life of the structure.
For example, structures that last less than 10 years fall into the category of temporary structures. When choosing the type of foundation, we don't need to pay as much attention as we would with a structure that will last 50 years.
Therefore, when selecting an appropriate foundation type, the importance and intended service life of the structure must be taken into consideration.
Superstructure loads
There are two main types of loads placed on foundations. There are vertical and horizontal loads. The article Types of Loads in Structures Discuss stresses in structures in more detail.
Additionally, the type of structure also affects the loads placed on the foundation.
- Type of structure: Whether the structure is a building, dam, retaining wall, steel tower, etc., it may affect the structural loads.
- Structure height: Especially in buildings, height is a crucial factor that influences the load on the foundation. As the number of floors increases, the permanent and dynamic loads on the foundation increase proportionately. Furthermore, increasing building height leads to increased wind load. Additionally, the number of floors increases the mass of the building, resulting in greater shear at the base of the foundation.
- When considering a retaining wall, the condition of the soil and the type of stability method affect the structural loads. Whether we consider active pressure or rest pressure is one of the main factors that affect the loads on foundations. The article Stability Analysis of Structures AND Lateral Earth Pressure Coefficients discusses this in more detail.
Effects of soil type on foundation type selection
One of the most important factors to consider when choosing foundation types is the type of soil.
Whether it is a shallow or deep foundation, the condition of the soil determines the type of foundation and the dimensions of the foundation.
Once the superstructure loads have been assessed, a decision can be made whether a shallow or deep foundation should be installed.
Soil investigation is carried out and recommendation is obtained from geotechnical engineers for a suitable type of foundation based on superstructure loads.
The type of foundation and the soil's support capacity are determined by the geotechnical recommendation used to construct the foundation.
When we consider a shallow foundation, it can be footings or slab foundations. The permissible load capacity and settlement depend on the terrain conditions.
For deep foundations such as in-situ concrete piles, micropiles, driven piles, etc., the soil type and nature of the rock must be taken into consideration when selecting the appropriate foundation type.
Influence of adjacent structures on the selection of the type of foundation
If buildings are arranged very densely, construction must be carried out in such a way that the existing structure is not damaged.
For example, if a basement is built in an area where the water table is very close to the ground, drainage is necessary for the construction of the basement.
If the adjacent building is built on a shallow foundation, drainage will lower the water table, which can cause the adjacent building to settle. The building may have cracks and neighbors will take measures to stop the work and receive compensation.
In these locations, care must be taken when building foundations in this way.
Available foundation types
Foundation type consideration depends on the foundation types available. At the beginning of this article, we discussed the available foundation types that could be considered.
Once the superstructure loads have been determined, we can consider the most suitable type of foundation depending on the nature of the soil on which the structure will be built.
Influence of construction costs on the selection of the type of foundation
Construction cost is an important factor to consider when deciding on a suitable foundation type.
Whether a structure should be built on shallow or deep foundations depends on the nature of the soil. However, there are other ways to select or suggest a suitable foundation type.
For example, imagine a building that needs to be built on weak ground, and that ground is weak up to a depth of 2.5 m. In this case, you can choose deep foundation types such as cast-in-place concrete piles, driven piles or micropiles.
Another option is to improve the soil to a height of 2.5 m and build a shallow foundation.
Selection of an appropriate method in an occasion of this nature could be based on construction costs.
Article, Ground Improvement Methods AND Ground Improvement for Low-rise Buildings Discuss the methods available for ground improvement on a smaller and larger scale.
