Essay Example: Types of Foundations for Construction

The type of foundation varies depending on the type of the building to be put up, the type of ground and the climate of the region where the building is to be constructed. Residential and commercial buildings require strong and firm foundations to enhance stability and security. However, based on budget and construction goals, the construction may be put up with different types of foundations.

Broadly, foundations are categorized into shallow and deep foundations. The terms shallow and deep define the depth that the soil is dug to make the foundation. A depth which is less than 3 feet (1metre) is considered to be shallow whereas deep foundations range between 60 and 200 feet (20 65m). Shallow foundations accommodate small and light buildings while deep foundations are for huge and heavy buildings (Allen, Thallon & Schreyer 2017).

Shallow foundations

These foundations are also referred to as spread or open footings. These foundations are made starting by excavating the top layer of the ground or earth to the base of the footing. At the start, the foundation can be seen, and the foundation is hence called open foundation. Ideally, each footing in the shallow foundation is to spread the weight concentrated on each column and spreads it across a large area to reduce pressure and so that the actual building weight does not exceed the safe carrying capacity of the particular soil.

Shallow foundations are protected from freezing in the cold climatic areas. This is because water demonstrates anomalous behavior in expansion and contraction. Water in the soil around the found can freeze and expand unusually thereby destroying the foundation. In these areas, foundations are made below the frost line contrary to which the foundation should be insulated. Insulation allows some heat to permeate into the soil from the building.

Types of Shallow Foundations

Shallow foundations are the raft foundations, strip footings, and, individual footings.

Individual Footing

These are the most common and the simplest type of foundations. They are applied where the building load is carried by use of columns. Each column will eventually have its footing. The footing is constructed by a square or rectangular pad made of concrete where the column sits. The engineer takes the total load of the column and divides by the safe bearing capacity (SBC) of the soil to arrive at the size of the footing. For instance, if the column has 20T and the SBC of the soil is 10Tm-2 then the area of the footing 2m2. However, the designing engineer will have to consider many other factors before coming up with a construction design for the footing. Individual footings are always connected to the plinth beam.

Individual footings connected by a plinth beamIndividual footings: concreting stage of the footing column.

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Strip Footings

These are commonly found on in load-bearing masonry constructions. The strip footings act as a long strip that holds the weight supported on the entire wall. The strip footings are used where building loads are to be supported by the entire wall as opposed to individual columns. These footings are suitable for most sub-soils with light structural loadings like those found in low to medium rise domestic houses where mass concrete is used.

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Raft Foundations

These foundations are also called Mat Foundations and are often used when basements are to be put up. It is referred to as raft because the building appears to float on the surface of the earth. In these foundations, the basement floor slab acts as the foundation where the weight of the building will be concentrated and evenly distributed to cover the whole footprint of the building. Raft foundations are adapted to spread the load of the structure being constructed over a surface area to reduce load per square units (pressure). These foundations are useful in low bearing capacity soils and where the individual column loads are heavy or closely spaced. The raft foundations are majorly applicable where commercial buildings that require large open spaces under the main building (Rogers et al., 2015).

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Deep Foundations

The main type of deep foundation is the pile foundation. A pile is a long cylindrical concrete material that penetrates deeply in to the ground such that the building the pile's support is held on top of it. The pile foundations are useful in the circumstances that either the layer of the soil is weak at the surface or the building is very heavy. When the layer of soil cannot support the load of the building, the load of the building is transferred to the stronger layer of rocks below the subsoil or the stronger soil beneath the weak layer of soil. Pile foundations can hold higher loads than open footings that are associated with high rise structures.

Pile foundations are classified into two types: End Bearing Pile and Friction Pile. The pile foundations are regarded to be a series of columns constructed or inserted into the grounds to transmit the load or loads of a building to lower levels of the subsoil. Pile foundations are used when suitable foundations are not present at or near ground levels thus making the use of deep traditional foundations uneconomical.

End Bearing Piles

In this pile foundation, the base end of the pile penetrate through the weak soil and rest on the strong soil below or rock. The pile transfers the weight of the building to the strong layer of soil below. In essence, the pile is the column of the building. In principle, the load of the high rise structure rests just on the intersection surface between the weak and the strong layers of soils. The load thus cuts through the weak layer to be held on the strong layer (Chudley & Greeno 2013).

Friction Piles

Unlike the end bearing piles, friction piles work on the principle that transfers the load of the building throughout the entire pile height by friction. The forces resulting from the building are transferred into the soil by the pile. The deeper the pile into the soil, the higher the weight it can support. Practically, each pile resists the amount of load through a combination of friction and the end bearing.

In conclusion, the type of foundation that a constructor will adopt will largely depend on the kind of climate experienced in that particular area, the type of soil as well as the building to be constructed.

There are majorly two types of foundations, shallow and deep foundations. There are also sub-types between these two types. The type of foundation chosen requires the builder to study carefully the soil type and climate so that measures to protect the foundation can be employed. For instance, if the foundation is in a place that experiences freezing and contraction, insulation is necessary to protect the foundation.

References

Allen, E., Thallon, R., & Schreyer, A. C. (2017). Fundamentals of residential construction. John Wiley & Sons.Rogers, N., van Ballegooy, S., Williams, K., & Johnson, L. (2015, November). Considering post-disaster damage to residential building construction-is our modern building construction resilient. In Proceedings of the 6th International Conference on Earthquake Geotechnical Engineering. Christchurch, NZ: ISSMGE.

Chudley, R., & Greeno, R. (2013). Building construction handbook. Routledge.