Types of Pile Foundations and Their Applications in Construction

Building Foundations are a vital step in the construction process. The selection of foundations depends on several factors, which shall discuss below. There are two types of foundations; Deep foundations and shallow foundations.

How is the categorisation made? When the topsoil in a construction site is suitable for supporting superstructures, shallow foundations are used as there is no need for soil extraction. When the topsoil quality is inadequate, engineers will perform soil extraction to find deeper soil strata with the required qualities. Technically speaking, if the Load Bearing Value, soil type (clay, sand, chalk, etc.), and soil properties (moisture content, reaction to climatic changes) can support the weight of the infrastructure, engineers will build shallow foundations. However, if the above attributes are inadequate, engineers must build deep foundations. 

As a simple rule, any foundation whose depth is lower than the footing’s width and lower than 10 feet is categorised as a shallow foundation. However, if the foundation’s depth exceeds the footing’s width, it is classified as a deep foundation.

Types of Deep Foundations

There are three types of deep foundations:

• Pile Foundations
• Well Foundations
• Caissons Foundations

We will be discussing only pile foundations in this article.

Applications of Piling

A Pile foundation or piling, as it is commonly known, is primarily used for transferring the weight of a superstructure through compressible, weak, or highly moist soil strata to less compressible, more compact, and stronger layers of soil or rock located deep under. This technique increases the effective size of foundations and resistance to horizontal loads. Therefore piling is often used for supporting large structures and in situations where the excessive settlement of the surface soil is expected. 

Pile foundations must withstand heavy loads and must be designed with extreme care. A competent engineer will conduct a detailed study of the soil layer to support the piles and prevent overloading them. Engineers must also ensure that the piles are kept apart at the proper distance to ensure uniform weight distribution on the soil below.

Types of Piles

Piles can be categorised based on several aspects. When you consider function, two of the most common types are :

• Friction Piles
• Bearing Piles

They can also be classified based on the material they are constructed from. These include :

• Steel Piles
• Sand Piles
• Concrete Piles
• Timber Piles

Bearing piles are installed for supporting vertical loads by transferring the superstructure’s weight to deeper soil layers below. Bearing piles are usually constructed from steel pipes, and they are prefered in two conditions.

First, when weak surface soil layers cannot support the load of new infrastructure. Second, when the topsoil cannot support the infrastructure regardless of the soil’s LBV( Load bearing value). Bearing piles offer several advantages over other piling types. For instance:

• They can be easily linked to the infrastructure above.
• They are long-lasting and highly durable.
• Piles of any length can be prepared
• They have a relatively easy installation.
• They can be used right after installation.

Some of the few types of bearing piles include box piles, tubular piles, wide flanges, and H-pile. When piles have to be fully sunk into the ground, as in the case of creating railway bridges and roads, wide flange and H-piles are considered more appropriate. Box and tubular piles work best for above-surface support, such as jetty and pier construction. 

Bearing piles are installed either as pre-cast driven or cast-in-place piles. Cast-in-place piles mainly utilise steel tubes which are inserted into the soil by hammering. The soil inside the pipes is removed, and a reinforced steel cage is lowered into the tube, followed by the pouring of wet concrete.

Pre-cast-driven piles are prepared according to the requirements. They can be prepared off or on-site. A pile driver hammers the vertically held pile into the soil. The pile has a temporary cap for avoiding damage while being hammered. The hammering continues till the pile refused to go any farther.

Like bearing piles, friction piling is also an underground piling technique. They create solid foundations supporting heavy buildings such as roads, bridges, and stadiums. As friction piles work like a wedge, they are also known as floating piles. They are ideal for sites where hard soil layers are difficult to reach. Friction piles transfer the weight from the low-quality topsoil to the strata below by friction or adhesion between the soil and the pile.

Friction piles are usually constructed from timber, reinforced concrete, or steel in the shape of columns. The piles extend below the structure by at least three times the width of the structure. They are available in several types, including wide flange and H-pile types. 

The depth and the thickness of the H-piles are both the same. They provide effective weight distribution over wide areas, making them highly suitable for supporting large and heavy structures. Each H-pile can tolerate up to 1000 tons of load.

Classification of Piling Foundations Based on the Effect of Soil:

Driven piles are also called displacement piles, as they displace the soil in lateral directions. They are commonly used when the topsoil does not have sufficient load-bearing value ( LBV ). Driven piles shift the load of the superstructure to deep and suitable strata providing the structure with the support it needs. 

Driven piles can be used to support a variety of structures, such as bridges, walls, towers, tanks, etc. They have other applications as well; these include retaining walls, bulkheads, and embankments. The four most common driven piles include:

• Pre-cast Driven Displacement Piles
• Cast-in-place Displacement Piles
• Cast-in-place Drilled Displacement Piles
• Cast-in-place Screw Displacement Piles

Driven piles are made from steel, timber, pre-cast concrete, and composite materials.

These are also known as replacement piles, as they replace the low-quality soil and transfer the load to more compact and stronger soil strata. Soil is removed/extracted in several ways, including screwing or driving. The spoil removal forms a hole which is filled with a reinforced concrete pile in situ. The pile replaces the spoil, which is why it is called replacement pile. 

Bored piles are primarily used when the soil has high cohesion or when existing buildings may be compromised because of construction activities. Bored piles can be drilled using buckets or augers, which are driven by rotary boring (twisting) or vibratory hammers (percussion boring). Some piling techniques use to carry out boring and pouring simultaneously, this is known as CFA (Continuous flight auger).

Screw piles are screwed/wound into the ground just like you use one on wood. These screws are made from hollow steel and have helices around them. The screw pile cuts through the soil to reach stronger layers. It is left there permanently and acts as an anchor. Concrete is poured over them to make them permanent. Screw piles are screwed into the ground with the help of hydraulic motors. They have many applications, such as roads, lighthouses, residential construction, etc.

Classification of Pile Foundation Based on Materials of Construction

Timber piles have been in use since ancient times. They are more commonly driven and include pre-cast piles. They can be highly affordable, safe, and efficient if properly designed and installed. Many historical buildings with timber piles have stood the test of time.

Steel is the preferred material of construction when it comes to driven piles. They are highly versatile and can range from small to very large diameter tubes. Steel tubes can be open-ended or closed and are driven with percussion or an oscillating hammer.

Concrete piles are common and often used to support offshore structures, including floating airports, oil rigs, and bridges.

Where are Pile Foundations Used?

Following are some of the situations where pile foundations are used:

• Very high groundwater table. (making the soil wet and making construction impossible)
• Non-uniform and heavy loads.
• When other foundations are much costlier to build.
• Highly compressible, loose, and moist soil.
• Sites very close to the seashore river bed or other water sources.
• Near drainage systems and canals
• If soil excavation cannot be carried out.
• They can also be used for reinforcing existing foundations.
• When there are many adjacent buildings which can be affected by noise or vibration, such as hospitals, populated areas, archaeological sites, etc.