Pile Foundations

Foundations provide structural support and load transfer from the structure to the soil. However, the layer through which the load is transferred by the foundation must have adequate bearing capacity and settlement characteristics. The two types of foundations are shallow foundations and deep foundations.

When the surface soil's bearing capacity is adequate to withstand the loads imposed by a structure, shallow footings are frequently used. On the other hand, deep foundations are often used when the surface soil's bearing capability is insufficient to withstand the loads imposed by a structure. The loads must therefore be transferred to a deeper level where the soil layer can support them better. The pile foundation is one of the deep foundation types.

A pile foundation Is a form of deep foundation used to support a structure and transmit stresses by end bearing or skin friction at chosen depths. It is a long, thin column made of steel or concrete. The use of foundation piles is often necessary for large constructions and situations where shallow soil cannot effectively withstand excessive settlement, uplift, etc.

Types of Pile Foundations

Pile foundations can be categorized according to their purpose, materials, installation method, etc. The classifications include the following:

• Classification based on usage.

• Classification based on materials and construction techniques.

• Classification based on effect of the piles on the soil.

Sheet Piles

The primary purpose of these piles is to offer lateral support. They typically withstand lateral pressure from things like water flow and loose soil. They are typically employed for shore protection, trench sheeting, and cofferdams. They are not employed to support the structure vertically. They typically provide the following functions:

• Building walls.

• Protection against erosion of riverbanks.

• Keeping the loose dirt in the vicinity of the foundation trenches.

• For separating the foundation from nearby soils.

• To contain soil and so boost the soil’s bearing ability.

Load Bearing Piles

The primary purpose of this kind of pile foundation is to transfer vertical loads from the structure to the ground. These load-bearing pile foundations transfer loads from a layer that is able to carry the load onto a layer of soil with weak supporting properties. Load-bearing piles can also be categorized as flowing depending on the method of transferring weight from the pile to the soil.

• End Bearing Piles

Loads travel via the pile’s lower tip in this type of pile foundation. The end-bearing piles’ bottom ends rest on a solid foundation of rock or dirt. The pile typically lays between a weak and strong slayer’s transition layer. The load is therefore safely transferred to the sturdy layer by the pile acting as a column.

The size of the pile's tip and the bearing capacity at the specific soil level where the pile is buried can be multiplied to determine the total capacity of an end bearing pile foundation. The diameter of the pile is computed while taking an acceptable safety factor into account.

• Friction Pile

The friction pile uses the frictional force between its surface and the soil surrounding it, such as stiff clay, sandy soil, etc., to transfer load from the structure to the earth. Depending on the underlying layers, friction may develop over the full length of the pile or along a specific length of the pile. In general, the entire pile surface contributes to the transfer of loads from the structure to the earth in friction piles.

The pile's capacity Is calculated by multiplying the surface area by the safe friction force created per unit area. While building a skin friction pile, it is important to consider a reasonable safety factor as well as the skin friction that will develop at the pile surface. In addition to this, one can raise the pile diameter, depth, number of heaps, and roughen the pile surface to boost the friction pile’s capacity.

Based On Materials And Construction Techniques

Timber Piles

Pile foundations that are buried beneath the water line typically use timber piles. They last for roughly 30 years on average. Both rectangular and circular shapes are possible. Their diameter or size might range from 12 to 16 inches. Typically, the pile’s length is 20 times its top width. Typically, they are made to support 15 to 20 tons. By fastening fish plates to the side of the piles, more strength can be obtained. An advantage of timber piles is that After installation, timber pile footings can be trimmed to any required length. Timber stacks can also be simply removed if necessary.

Concrete Piles

• Precast Concrete Piles

If the precast concrete piles are rectangular in shape, they are cast in a pile bed with a horizontal form. Generally, circular heaps are cast in vertical configurations. Steel reinforcement is typically added to precast piles to avoid breakage as they are moved from the casting bed to the site of the foundation. After the piles are cast, the required curing must be carried out. Pre-cast piles typically require 21 to 28 days to cure. These piles have high strength and possess high resistance to biological and chemical attack.

• Cast in Place Concrete Piles

This kind of pile footing is built by drilling a hole in the earth to the necessary depth, adding freshly mixed concrete there, and allowing it to cure. Cast in situ concrete pile foundations are built by either driving a metallic shell into the ground, filling it with concrete, and then either pulling the shell out while the concrete is being poured, or both. Cast-in situ piling frequently employs round piles.

• Steel Piles

Steel piles can be made of hollow pipes or I-sections. They are concrete-filled. The diameter can range from 10 inches to 24 inches, and the typical thickness is 34 inches. The piles are simple to drive because of their tiny sectional area. Most often, they serve as end-bearing piles. Even though they can be prone to corrosion, steel Piles are easy to install, can reach greater depth and they can penetrate hard soil layers with much ease when compared with the other types of pile foundations.

Based on Effect on the soil

• Driven Piles

Driven piles, often referred to as displacement piles, are a popular kind of building foundation that supports structures by transferring their weight to strata of rock or soil that are strong enough to hold the weight and have the right settlement properties. Driven piles are frequently employed as the most economical deep foundation method to support buildings, tanks, towers, walls, and bridges. Moreover, they can be utilized in projects like cofferdams, retaining walls, bulkheads, anchorage structures, and embankments.

• Bored Piles

Replacement piles, often referred to as bored piles, are a type of construction foundation that is frequently used to support structures by shifting the weight of the structure to layers of rock or soil with adequate bearing capacity and proper settling characteristics. Bored piles are piles where the removal of debris creates a hole for an in-place pour of reinforced concrete. The term “replacement” pile refers to a pile that replaces the spoil as opposed to a displacement pile, which forces soil away by driving or screwing the pile. For the construction of friction piles and pile foundations adjacent to existing structures in cohesive subsoils, bored piles are generally used. They are well-liked in cities because there is little vibration and little headroom there.

• Screw Piles

For the purpose of screwing the piles into the earth, a helix is present near the pile toe in screw pile foundations. The method and idea are comparable to screwing into wood. Depending on the purpose and the ground circumstances, a screw pile may contain more than one helix, also known as a screw. If a heavier load is necessary or softer ground is encountered, more helices are typically supplied.

When To Use Pile Foundations

The following circumstances call for the use of pile foundations:

• When a thin layer of porous soil is present at the surface. The loads of the building must move beyond this layer and onto the layer of firmer soil or rock that is beneath the weak layer since it is unable to hold the weight of the building.

• When a structure, such as a high-rise skyscraper, bridge, or water tank, is subject to exceptionally heavy, concentrated loads.

• When scouring is a possibility since it is close to a riverbed, the beach, etc.

• When a deep drainage system or canal is located close to the structure.

• When unfavorable soil conditions prevent soil extraction from reaching the specified depth.

• When the amount of seepage makes it impossible to pump or take any other action to keep the foundation trenches dry.

Spread footings cannot support the same loads as pile foundations. The foundation engineer must select a foundation for the structure from among the several forms of pile foundation whenever one of the aforementioned conditions—where pile foundations are appropriate—occurs.

Factors Considered When Selecting Type of Pile Foundations

There are various pile foundation types that can be used for a certain project. A select few parameters determine which kind of pile foundation is used. These factors are noted below:

• Type and superstructure loads.

• Features of soil.

• The depth of the soil layer beneath the piles that can support them.

• Required variations in pile length.

• Materials are readily available.

• Durability of the foundation.

• Obtainable tools for driving piles.

• Budget.

• The level of water below earth and how strongly it is flowing.

• Types of surrounding structures.

Causes of Failure in Pile Foundations

When bad soil conditions are present at a short depth and a structure is heavily laden, pile foundations are one of the most preferred options. Yet, pile foundations can fail for a variety of causes. Before developing pile foundations, suitable safety measures must be taken to minimize the risk of such failure. These are some reasons why pile foundations fail:

• The pile’s suggested load is higher than its intended load.

• End bearing pile on soft strata.

• Incorrect soil analysis.

• Choosing the incorrect kind of pile.

• The pile is not adequately reinforced.

• A piles-decay. (such as pest invasion, rust, etc.)

• Pile deformation brought on by lateral stresses.

• Incorrect pile capacity estimation.

• Not taking into account lateral stresses while designing piles

Machinery For Driving Piles Into The Ground

There are several equipments used for driving piles into the ground. They include:

Pile Drivers

Pile drivers are construction equipment used to force piles into the ground for foundational support in structures like buildings and bridges. They can be operated using different methods such as mechanical, hydraulic, or vibratory, depending on the specific requirements of the project.

• Diesel hammers

Diesel hammers are impact pile drivers powered by diesel fuel. They generate force through the combustion of diesel and an air mixture, driving piles into the ground with repeated, high-energy impacts.

• Hydraulic hammers

Hydraulic hammers are pile driving equipment that use hydraulic systems to generate force for pile installation. These hammers offer precise control and are suitable for a variety of soil conditions and pile types.

• Vibratory pile drivers

Vibratory pile drivers are machines that utilize high-frequency vibrations to drive or extract piles with minimal soil displacement. They are particularly effective in granular soils and can be used to install sheet piles, H-beams, and other pile types.

• Press-in pile drivers

Press-in pile drivers are silent, low-vibration equipment that installs piles through steady hydraulic pressure. They minimize noise and vibration, making them ideal for use in urban environments or sensitive areas.

Universal drilling machines

Universal drilling machines are versatile drilling equipment designed to handle various ground conditions and adaptable for multiple drilling methods. They can perform tasks such as rotary drilling, auger drilling, and core drilling, making them essential for a wide range of construction and geotechnical projects.

Sectional flight auger

The sectional flight auger is a helical tool used in continuous flight auger (CFA) drilling, which removes soil while simultaneously installing piles. This method combines drilling and pile installation in a single operation, reducing construction time and improving efficiency.

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