The significance of a foundation goes beyond just being able to support the structure above. It is also considered to be a construction that ensures that the structures are not at all affected by the environmental conditions and maintains the longevity of the structures. However, one thing that most people need to learn about foundations is that there are two main types of foundations: shallow foundations and deep foundations. To help you understand the difference between shallow and deep foundations, this extensive guide on what shallow foundations and deep foundations are could really help.
What is a foundation?
The literal meaning of a foundation in construction is the element that connects the structure to the ground. It is located at the very base of the building, is in direct contact with the soil, and helps to transfer load from the structure to the ground safely.
The foundations are also considered to be the first part of any construction. They are also essential for the durability of the building, and if not completed correctly, they could affect its strength once the construction is over. In short, if the foundation is improper, there is a high chance that the building will be unreliable or will not last for long.
Types of foundations
There are two primary types of foundations available and used in construction: shallow foundations and deep foundations. Each type has unique attributes and applications based on factors such as soil conditions, structural demands, bearing capacity, financial considerations, and site limitations.
Understanding the essential characteristics of the two types of foundations and the difference between shallow and deep foundations can help engineers and architects make informed decisions. It also helps them decide which of the two types would be an excellent match for the project type. Here, we will understand what each of these foundations is and how they differ from each other.
What are shallow foundations?
What are shallow foundations? Well the first of the two types is the shallow foundation. This type of foundation helps to transfer the building’s weight to the soil by being extremely close to the surface instead of deep into the earth. It helps distribute the building’s weight across a much wider space near the surface. The seismic activity, the soil type, and the project type will need to fit the suitability.
There are also a lot of advantages to shallow foundations. Here are a few of them:
- It requires only a shorter construction timeline, which means the project will be finished faster
- They are generally more economical as compared to the deep foundations
- There is less of a requirement for complex instructions, and hence, they are easier to implement.
Types of shallow foundation
Shallow foundations are often the best suited for small buildings. The depth of the foundation is usually less than its width in the shallow foundation type. Here are a few different types of shallow foundations that are often seen in construction.
Strip Footing
A strip footing is added on for a load-bearing wall. A strip footing is also provided for a row of columns that are closely spaced so that their spread footings tend to overlap or almost touch each other. In such a case, it is more economical to provide a strip footing rather than giving many spread footings in a line. A strip footing is also often called a continuous footing.
Isolated Footing
Isolated footing, also called spread footing, individual footing, or pad footing, is added to support a single column. It is usually a square, circular, or rectangular slab of uniform thickness. Sometimes, it is haunched or stepped to spread it over a larger area.
Combined Footing
A combined footing is used when support is needed for two columns. It is used when the two columns are so close to each other that their footings are often seen to overlap. A combined footing could either be trapezoidal or rectangular in plan.
Raft or Mat Foundation
A raft or mat foundation type is nothing but a large slab that supports some columns and walls under a large part of the building. A mat is usually required when the soul pressure is low or when the walls and columns are so close that the individual footings start overlapping or touching each other.
Cantilever or Strap Footing
A cantilever or strap footing consists of two isolated footings connected with a lever or a structural strap. A strap or isolated footing is much more economical than a combined type of footing, especially when the soil pressure is relatively high and the distance between columns is significant.
What are deep foundations?
Next, we need to look at deep foundations. Deep foundations transmit the weight of the structure further down into the depth of the earth than shallow foundations. Typically, the depth-to-width ratio could be anywhere between 4 and 5. In practical terms, if the value of width is W, then the depth could be 4 or 5 times greater than this value.
There are a lot of benefits when it comes to deep foundations, and a few of them could be provided as follows:
- Deep foundations are constructed in such a way that they can carry heavy loads, which makes them strong enough to hold a large building.
- Even if there is the presence of unstable soil conditions, deep foundations could be used.
- Deep foundations offer excellent resistance when it comes to natural solid forces such as winds or earthquakes.
Types of deep foundations?
When the soil pressure is not good enough, you need a proper foundation that can hold the weight of the building well. In such cases, a deep foundation is the right way forward. However, various types of deep foundations are commonly used in construction and can be found in the following:
Pile Foundations
Pile foundations are a type of deep foundation that involves vertical piles or columns that are either drilled, driven, or cast into deep ground. These piles tend to transfer the structure’s heavy loads to the deeper layers of the soil. However, their suitability will depend highly on climatic conditions, soil types, and the construction project site.
Basement Foundation
A structure with more than one floor below ground level uses a basement foundation. All foundations, except for the basement foundation type, are partially hidden. The special feature of a basement foundation is the ability to build a completed basement that can serve as a multipurpose space or regular room beneath the main building.
Well, or Caisson Foundation
Wall or Caisson foundations are structural elements that mainly support massive constructions such as bridges or piers. They are usually cylindrical and are often immersed underwater during construction to provide support and stability in difficult situations.
Shaft Foundation
Shaft foundations, often called drilled piers, are versatile building elements used worldwide. In its most basic form, a drilled shaft foundation is built by boring a cylindrical hole into the ground, adding a reinforcement cage, and filling the borehole with concrete.
Buoyancy Rafts
A foundation type that is dependent on the principle of buoyancy is the buoyancy raft foundation. Because of this, the foundation’s differential and total settlements are reduced by lowering the total load on the soil.
There are quite a few contrasts between deep and shallow foundations. The concept, the thickness of the foundation, the price, and even the method of load transfer differ a lot. To understand the difference in depth, here are a few points that highlight it.
| Criteria | Shallow foundation | Deep foundation |
| Depth of foundation | It is no more profound than the footing or not more than three meters deep | It is thicker than the thin foundation |
| Complexity of construction | Simple type of construction | Much complex construction with the need for specialised equipment |
| Cost | Much more economical | Typically expensive due to specialised equipment being involved |
| Load bearing capacity | Much suited for lighter structures | Better suited for heavier structures and structures with high vertical loads |
| Time efficiency | Require shorter timelines for construction | Requires longer timelines for construction |
Factors affecting the choice of foundation
The right foundation is essential for ensuring a structure’s stability and longevity. Here are a few of the factors that affect the foundations chosen for each type of structure.
Soil Type and Bearing Capacity
Soil is the most fundamental connection between the structure and the earth, which makes its properties very significant when choosing the foundation design. Different types of soil have varying strengths, expansion potential, and compressibility.
Project Load Requirements
The magnitude and nature of the weight imposed by the structure are also factors, apart from external factors such as seismic activity and wind, that affect the decision of which type of foundation is best.
Budget and Time Constraints
Comparing the financial effects of deep and shallow foundations is essential since every project in the construction line is based on a fixed budget and timeline. Deep foundations are a bit more expensive and time-consuming than their counterpart.
Environmental Impact
The environmental impact of construction activities has become one of the major concerns and needs to be considered. Areas with elevated water tables require a particular type of foundation that prevents groundwater contamination. Similarly, in ecologically sensitive sites, it is essential to keep the disturbance to a minimal amount.
Structural Design
It is also essential to consider the project’s structural design requirements, including the type and amount of loads being exerted. The overall design could also affect whether you require a deep or a shallow foundation.
Regulatory Approval
Checking the local building codes and regulations is essential to ensure that the foundation’s standards are being diligently met. Specific rules may also influence the type of foundation you choose.
Application in Construction
Shallow foundation types are best suited for lighter structures. The closeness of the bedrock to the surface is often what determines the use of shallow foundations. When the bedrock is much nearer, it can provide the necessary support for the structure while eliminating the need for a much deeper foundation. Deep foundations, on the other hand, are best suited for heavy structures or in situations where the upper soil layers are too inconsistent or weak to bear the load of the structure. In such cases, the foundation should be able to bypass these layers and transmit the overall weight to a much deeper and stronger layer.
FAQs:
When you are working with shorter and lighter structures, you only need a shallow foundation.
There are a few disadvantages when it comes to deep foundations, and they can be provided as follows:
They are generally expensive due to the complex process
It tends to have a more time-consuming process
Not suitable for lighter structures or projects that have strict budgets
One of the main reasons why there is a higher expense in deep foundation installation is the requirement for a large number of materials and labour for construction.
Yes, most foundations can often be repaired. It could be a minor crack repair or even water seepage issues.
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