Piling

What is a Pile?
A pile is a type of deep foundation through which the load of a structure is transferred. Piling is done in areas where the soil’s bearing capacity is very low. The pile helps distribute the load of the structure. The decision about whether the foundation will be deep or shallow is made based on the soil test report. Piling design is carried out according to the soil test report. Before constructing any building, the site must first be selected. Piling work is generally performed in multi-story buildings based on the nature of the soil at the site.

Piling is a type of foundation for buildings or structures that transfers the load deep into the soil, providing a stable base for the structure. It is typically used in areas where the soil’s bearing capacity is low, especially for multi-story constructions. It can be compared to columns of a structure that are embedded deep into the ground.

When is Piling Done?
Piling is done when water starts to invade an area, such as a pond or coastal region, or when the banks of a river or pond begin to erode and threaten to submerge into the river or pond. It is done to protect one’s homestead from such dangerous conditions, to save lives, to preserve homes, and to safeguard the harvest accumulated over a lifetime. Piling is a type of foundation for buildings or structures that transfers the load deep into the soil, providing a solid base for the structure. Before constructing a building, piling should be done to increase the soil’s load-bearing capacity before proceeding with the construction.

What Are the Types of Piles?
Piles are primarily of two types:

1. According to Usage
2. According to Construction Material

According to usage, there are seven types of piles:

1. Bearing Pile
2. Friction Pile
3. Sheet Pile
4. Anchor Pile
5. Batter Pile
6. Fender Pile
7. Compaction Pile

Piling Types According to Construction Material
Piling can be of several types according to the construction material:

1. Shore Pile
2. Sand Pile
3. Timber Pile
4. Steel Pile

Shore Pile: Shore piles are installed to resist lateral soil pressure. In structures with basements or where excavation is necessary for other reasons, this system is implemented to prevent damage to the adjacent soil. It can be compared to a shear wall. Shore piles can be precast, cast in situ, or timber piles.

Sand Pile: Although the concept of sand piles is relatively new, it can be quite effective in certain situations. Generally, sand piles are used in low-rise structures where the soil’s bearing capacity is low. However, it is not applicable for high-rise buildings. Sand piles are created by excavating a hole in the ground and filling it with sand. This method is employed to increase the bearing capacity, as sand can bear more load than soil. The hole is made using augers or by inserting a hollow pipe with the bottom closed, and pressure is applied to create the hole.

The diameter of the hole typically ranges from 20 cm to 40 cm. After excavation, the hole is filled with sand and compacted firmly. The sand is kept moist during compaction. To protect the pile from lateral pressure or to safeguard the filled sand, the top of the pile is filled with 1 meter of cement concrete. These piles can be constructed from 2 meters to 5 meters deep. Generally, the piles are placed beneath columns.

Timber Pile: Timber piles are made from tree trunks (usually Sal tree trunks) used as piles. They are utilized for low-rise buildings. Timber piles are advantageous for constructing light structures on wet and compressible soils, and they are also cost-effective. The load is distributed by the friction between the soil and the pile surface. Timber piles are primarily used as friction piles. Timber can be sourced from trees such as Sal, Teak, Cedar, Babool, and Khair. Khair timber is used in coastal construction as it does not deteriorate in salinity.

Wooden piles can be square or cylindrical. The diameter of cylindrical wooden piles ranges from 30 cm to 50 cm, while the dimensions of square piles range from 30 cm to 50 cm. The length of wooden piles should generally not exceed 20 times the upper dimension of the pile. The bottom part of the pile is tapered, and a CI shoe is used at the lower end for ease of installation. During installation, a ring with a steel plate is used to protect the upper end of the pile from damage; however, the diameter of the ring should be at least 25 mm smaller than the pile head.

Steel Pile: Steel sheet piles are long structural sections that create a continuous wall with a vertical interlocking system. These walls are often used to retain soil or water. The capacity of a steel sheet pile section depends on its geometry and the soil into which it is driven. The wall transfers pressure from the top of the pile wall to the front soil. Compared to robust concrete walls, construction with steel piles is significantly faster.

Advantages of Steel Piles

• Permanent sheet piling is a narrow form of construction that can be installed close to the site boundaries, maximizing usable site space.
• Steel sheet piles are suitable for all types of soil.
• There is no need for excavation for wall foundations.
• There is no disruption to the existing land for monotonous concrete piling.
• Steel materials have factory quality compared to site quality.
• Steel sheet piles can be easily made aesthetically pleasing.
• Steel sheet piles can be installed in advance for other works.
• Immediate load-bearing capacity is available.
• Steel sheet pile work can be used as a curtain wall to contain the work site.

The Main Purposes of Steel Piles

Steel piles serve several purposes, particularly in construction and deep foundation work. Below are some of the key purposes of steel piles:

1. High Strength and Durability: Steel piles are extremely strong and durable. They can bear heavy loads and remain stable over long periods.
2. Adjustability in Size and Length: Steel piles can be easily cut and joined to various sizes and lengths, making them adaptable to the needs of construction projects.
3. Reusability: Steel piles are reusable, meaning they can be used again in new projects after their initial use, making them environmentally friendly and cost-effective.
4. Deep Foundation Installation: Steel piles can be used in deep foundations and remain stable in soil or water. They are effective in soil, mud, sand, and soft terrain.
5. Ease of Connection: Steel piles can be easily connected to other piles, making them effective in building tall structures.
6. Variety in Design and Types: Different types of steel piles are available, such as H-piles, pipe piles, and sheet piles. Suitable types of steel piles can be used based on the needs of the project.
7. Earthquake Resistance: Steel piles are earthquake-resistant and help maintain foundation stability during vibrations.
8. Use in Challenging Locations: Steel piles can be used in weak soil or adverse environments where other piling materials may not be as effective.

Due to these advantages, steel piles are widely used in various construction projects, especially for high-rise buildings, bridges, and coastal structures.

What are the methods of pile installation?

The methods of pile installation are primarily determined by the type of soil and the type of pile being used. Generally, the following methods are used for pile installation:

1. Driving Method
   This is the most common method of pile installation. In this method, the pile is driven into the ground using a heavy hammer or vibratory driver. The pile head is repeatedly struck, causing it to gradually penetrate deep into the ground. This method is often used for installing steel, concrete, or timber piles.
2. Vibration Method
   In this method, a vibratory hammer or driver is attached to the top of the pile, and the pile is inserted into the ground through rapid vibrations. This method is effective for soft or sandy soils.
3. Jetting Method
   In this method, high-pressure water flow is used along the sides or under the pile to soften the soil. The water flow loosens the soil, making it easier for the pile to penetrate the ground. This method is suitable for sandy or soft soils.
4. Boring Method
   In this method, a hole is first drilled in the ground, approximately the size of the pile. The pile is then placed into this hole. Boring machines are typically used based on the type of soil. This method is effective for harder soils.
5. Screw Piling Method
   In this method, the pile has a helical blade at the bottom, which screws the pile into the ground like a screw. The resistance of the soil is reduced by the screw pile, allowing it to enter the ground. This method is usually used for light structures.
6. Drop Hammer Method
   In this method, a heavy hammer weighing about 60 to 100 tons is dropped from a specified height onto the pile. The pile gradually penetrates the ground due to the repeated impacts. This method is commonly used for hard soils.
7. Hydraulic Pressing Method
   This method uses a hydraulic machine to slowly press the pile into the ground. It is a silent and low-vibration method of pile installation. It is often used in areas where noise and vibration need to be minimized.

These methods are selected based on the location, soil condition, and structural requirements for the pile installation.

Methods of Casting Concrete Piles:

1. First, a hollow tube or hollow steel pipe casing is driven into the ground by impact. Then, concrete is poured into the hollow tube. Such piles typically range in length from 21 to 24 meters.
2. Even after the concrete has been cast inside the casing pipe, the casing pipe is not removed until other piles within a 3-meter radius have been installed.
3. Reinforcement rods are generally not used in this type of concrete pile. However, if a reinforced concrete pile is required, a steel cage is first placed inside the casing and then filled with concrete.
4. Special care must be taken to prevent rusting on the casing pipe.

Construction Method:

1. Formwork should be prepared according to the size and shape of the pile. If there are multiple piles, it is better to use metal formwork. Before filling the form with concrete, oil or a soap solution is applied to prevent sticking.
2. Reinforcement rods are used in the pile according to the design, not only to bear the structural load but also to facilitate handling and installation. Typically, 4 to 8 longitudinal rods with diameters between 20 mm to 50 mm are used, while the tie rods range from 6 mm to 10 mm in diameter. The tie rods are placed either horizontally or spirally. The spacing between the tie or spiral rods at the top and bottom 1 meter of the pile should be 80 mm to 100 mm, while the spacing in the middle section should be 300 mm. A 50 mm concrete cover is maintained. For easier installation, cast iron shoes and steel straps are used at the pile ends.
3. Concrete is poured into the form and vibrated properly for compacting. Generally, a concrete mix of 1:2:4 is used with a maximum coarse aggregate size of 19 mm. However, for piles needing to bear higher loads, a 1:1.5:3 concrete mix is used. Since the pile’s top part gets damaged during installation due to impact, higher-grade concrete of 1:1:2 mix is used for the top 0.6 to 0.9 meters.
4. Formwork is removed after 3 days of casting, followed by curing at the site for at least 7 days. The pile is then moved to a curing tank, where it is cured for 4 weeks before being driven into the ground.

In Bangladesh, primarily two types of piles are used:

In the case of permanent structures, where additional load-bearing capacity is required, concrete piles are used. The RCC (Reinforced Cement Concrete) piles are made by combining cement concrete with MS rods, which have gained popularity recently. Concrete piles can be mainly classified into three categories:

1. Precast Piles: These piles are generally manufactured at a convenient location away from the construction site. The design of the pile is prepared in advance, and concrete is cast accordingly. Later, they are installed at specific locations by applying load according to the layout. The shape of the piles can be circular or square, with a side cover of 50-75 mm. They are then driven into the ground at the site using machinery or hammering.

Precast concrete piles are used in permanent structures where additional load-bearing capacity is required. These piles are cast and cured at a convenient location away from the construction site before being brought to the site for installation. The piles can be round, rectangular, square, or octagonal, with diameters ranging from 35 cm to 65 cm and lengths varying from 4.5 meters to 30 meters.

• Cast-in-Situ Piles: These piles are constructed by first boring a hole to a specified depth according to the design layout. An iron cage is then inserted into the bore, followed by pouring concrete. The shape of these piles is always circular, with a side cover of 75 mm. Cast-in-situ piles are the most commonly used in Bangladesh because they can be easily constructed anywhere.

When concrete piles are cast using only cement, sand, and gravel or stone chips, they are referred to as plain concrete piles. If they are made with reinforcement, they are called reinforced concrete piles. Among these, cast-in-situ piles are the most prevalent. They are generally cylindrical, with diameters ranging from 18 inches to 30 inches, though they can be larger in some cases. The length depends on the soil layers, as indicated in the soil test report. Most multi-story buildings in Bangladesh have used this piling method.

Reasons for Piling:

1. When the weight of the superstructure is excessive and there is a need to distribute the load unevenly.
2. When the load-bearing capacity of the upper layer of soil is low. Piling serves as a type of foundation for buildings or structures that transfers the load deep into the ground, providing a solid base. It is typically done in areas where the soil’s load-bearing capacity is low, but the structure is multi-storied. This can be compared to the columns of a structure that are installed deep into the ground.
3. When the water level of the subsoil is consistently variable.
4. When a canal or deep drainage line is located next to the foundation.
5. When there is a possibility of water scouring the foundation in river or coastal areas.
6. When there is a need to resist lateral pressure.
7. When the upper layer of soil is expansive in nature.
8. To prevent soil erosion.

Detailed Discussion on Pile Caps:

1. The pile cap is a crucial part of a building.
2. The pile cap transfers all the loads of the building to the piles.
3. A pile cap with equal length and width is called a square pile cap, while one that is longer in length than in width is referred to as a rectangular pile cap.
4. The thickness of the pile cap depends on the soil’s bearing capacity and the load of the building.
5. The rods in the pile cap are generally single-layered, but in many cases, they are double-layered.
6. The rods in the pile cap are subjected to tension or compression.
7. Before pouring the pile cap, we break the top of the piles to expose the rods. We then perform dressing and leveling with sand under the pile cap, compact it with water, and place a polyethylene sheet before pouring concrete (during the concrete pouring, care should be taken not to spill onto the top of the piles). Afterward, the rods are bound, and formwork is done for pouring.
8. Due to the greater thickness of the pile cap, it should be well-vibrated to ensure that there are no voids inside.
9. During the pouring of the pile cap, care should be taken to ensure that the alignment of the columns is not affected.
10. Proper curing must be done.
11. When removing the formwork, care should be taken to avoid any damage to the pile cap.

What is a Pile Cap?

A pile cap is a robust concrete plate or panel that is placed on top of multiple piles. It connects the piles and helps distribute the load of the building’s structure evenly across the piles.

Why is a Pile Cap Used?

The purposes of using a pile cap are:

1. Load Distribution: The pile cap helps distribute the weight or load of the building evenly across the piles, ensuring stability and safety.
2. Increased Stability: The pile cap enhances the stability and strength of the structure. It creates a solid foundation based on the soil, protecting it from any future loads or movements.
3. Integral Connection: The pile cap connects various piles, resulting in a sturdy structure capable of supporting multiple piles.
4. Weather Resistance: The pile cap protects the piles from the effects of soil changes and weather conditions.
5. Facilitated Construction: The pile cap simplifies the construction of other parts of the building, such as columns and beams.
6. Precise Positioning: The pile cap ensures the correct positioning of the columns, which is essential for the overall stability of the building.
7. Compact Space Management: It helps in utilizing the construction site effectively, especially in areas with limited space.

The use of a pile cap ensures the safety and stability of the building, providing a lasting foundation.

Why is the head of the pile broken?
The head of the pile is broken for various reasons, which are outlined below:

1. Installation of Pile Cap: The head of the pile is broken to level the upper part of the pile, making it easier to install the pile cap or other components.
2. Achieving Required Height: Sometimes, the head of the pile may be broken to increase its height so that it aligns with the specific height required for construction.
3. Ensuring Quality: Breaking the head of the pile ensures that there are no cracks or weaknesses in the upper part of the pile, which could affect its stability in the future.
4. Load Distribution: Breaking the head of the pile ensures that the load is distributed evenly across the pile.
5. Preparation for Concrete Pouring: Breaking the head of the pile ensures the correct shape and configuration for concrete pouring.

These reasons are essential for ensuring the functionality of the pile and the quality of the construction site.

Pile Cap Check List

• Remove any weak concrete from the top of the piles.
• Seal all holes or gaps in the shuttering.
• Ensure that all site levels are plumb (vertically straight).
• Check the support of the shuttering properly to prevent it from collapsing during pouring or to avoid thick concrete.
• Mark the concrete pouring level on the shuttering.
• The horizontal supports of the column’s reinforcement bars must be above the concrete level.
• Check the clear cover thoroughly.
• Ensure that no part of the binding wire for the reinforcement bars goes inside the concrete cover.
• Install column rings at the bottom, middle, and top, placing one ring four inches above the concrete.
• Keep the column’s reinforcement bars plumb (vertical/upright).
• Clean the area thoroughly before pouring the concrete.

If the diameter of the pile is 20 inches, what will be the size of the chisel or cutter?
Answer: If the diameter of the pile is 20 inches, the chisel or cutter is generally 2-3 inches smaller than the pile diameter. Therefore, the size of the chisel or cutter will be approximately 17 to 18 inches.
The size of the chisel depends on the width of the excavated hole and the need to ensure the proper placement of the pile, so this measurement may vary slightly.

· What is the bottom covering or the lower CC of the pile?
Answer: It will be 1.5 to 2 feet.
For the bottom covering or lower CC (concrete) of the pile, the following rules are generally followed:

· Bottom Covering: The concrete covering below the pile is typically between 2 inches (50 mm) and 3 inches (75 mm). This is necessary to protect the lower part of the pile.

· Depth of CC: The depth of the CC can vary based on the construction project. Generally, at least 4 inches (100 mm) of CC is provided for the lower level of the pile.

· Requirements: The covering and depth of the CC should be determined based on local construction regulations and the specific requirements of the project.
It is advisable to consult local construction codes and engineers for accurate information for your project.

3. What is the formula for the spiral?
Answer: Nπ(D+d) +8dN\pi(D+d) + 8dNπ(D+d) +8d

4. What is the wash time for piles?
Answer: 30 minutes or until clean water stops flowing out.

5. What is the formula for the volume of a pile?
Answer: πD24×H\frac{\pi D^2}{4} \times H4πD2​×H

6. What is the typical clear cover for piles?
Answer: It is usually 3 inches.

State the dimensions of the inner ring of the pile.
Answer: The formula for determining the dimensions of the inner ring of the pile is: πD\pi DπD (where DDD is the diameter after excluding the side cover, spiral, and main rod diameter).

The formula for determining the length of the spiral is: πDHS\frac{\pi DH}{S}SπDH​ (where DDD is the diameter after excluding the pile diameter, HHH is the height of the pile, and SSS is the distance along the spiral).

What is meant by a pile cap?
Answer: A pile cap is necessary to connect the tops of the piles to the main foundation. If the main foundation is built on top of the piles, any movement can cause the foundation to shift. This can lead to lateral displacement or uneven settling of the foundation. Therefore, the tops of the piles need to be leveled and embedded in the foundation, and then covered with concrete. The structure created at the connection point between the piles and the main foundation is referred to as the pile cap.

Things to Consider During Piling

Important considerations must be taken into account during piling. These are as follows:

1. Ensure the work is being done according to the structural design.
2. Check that the necessary equipment and materials are properly available on-site.
3. Confirm that wash boring is being carried out until mud comes out with water.
4. Ensure that the minimum distance between two piles is at least 6 feet.

Some important factors to keep in mind during piling include:

1. Pile Position: Ensure the correct positioning of piles so that they align with the construction design.
2. Soil Testing: The soil’s characteristics should be examined before piling to understand its strength and load-bearing capacity.
3. Soil Depth: Ensure the appropriate depth for driving or installing the piles.
4. Equipment Inspection: Ensure the equipment and machinery used for piling are functioning properly.
5. Concrete Quality: Ensure the quality of the concrete used for constructing the piles.
6. Covering: Before pouring concrete over the piles, ensure proper covering (soil or pile cap) is in place.
7. Vibration: Ensure that air bubbles are removed from the concrete during pouring by applying vibration.
8. Curing: Proper curing should be done after pouring the concrete to ensure it gains strength.
9. Leveling: Ensure proper leveling of the pile heads so that they are installed correctly.
10. Safety Measures: Ensure safety measures are in place at the worksite so that workers can work safely.

By observing these factors, it is possible to ensure the quality and durability of the piling work.

Importance of Piling in Multi-Story Buildings

Piling is a crucial part of constructing multi-story buildings, as it helps establish and secure the foundation’s stability. Given the significant weight typically associated with tall buildings, piling is essential for anchoring this weight deep into stable ground layers. The importance of piling in such projects includes:

1. Ensuring Stability and Strength
   Piling enhances the building’s stability and strengthens its foundation. This ensures that the building remains firmly anchored and is not easily impacted by ground movement.
2. Increasing Load-Bearing Capacity
   Different soil layers have varying capacities to bear pressure. Piling transfers the building’s load to deeper, more stable layers, essential for high-rise structures.
3. Preventing Ground Settlement
   During construction, there is a risk of soil shifting or settling. Piling minimizes this risk, protecting the building from potential ground settlement.
4. Proper Load Distribution
   Piling distributes the building’s weight to deeper layers, preventing unnecessary stress on surface soil layers and providing long-term stability.
5. Earthquake Resistance
   In earthquake-prone areas, piling creates a secure foundation, improving building stability during seismic activity.
6. Adaptation to Soil Conditions
   Urban areas may have diverse soil types. Piling is crucial in soft or marshy soils where the ground cannot provide a strong foundation for buildings.
7. Increasing Building Longevity
   Correct piling extends the building’s durability and lifespan, ensuring a secure foundation that supports the structure’s long-term usability.
8. Cost Savings
   Although piling may increase initial costs, it reduces future repair expenses and risks, making it cost-effective in the long run.

Conclusion:
Piling is indispensable for multi-story buildings as it ensures the building’s stability, safety, and durability. It safeguards against natural calamities and stabilizes the foundation, enabling the building to remain reliable for many years.

Why Pile Caps are Used?
The main reasons for using pile caps are as follows:

1. Aid in Load Distribution
   Pile caps help distribute the structure’s weight evenly across multiple piles. This prevents unnecessary pressure on individual piles, safeguarding them from cracking or shifting.
2. Increase Stability of Piles
   Pile caps bind piles together, increasing their stability. This unification protects the piles against natural forces, such as earthquakes and ground pressure.
3. Strengthen and Stabilize the Foundation
   Pile caps enhance the strength and stability of a building’s foundation. They provide a solid base, independent of the underlying soil layers, especially useful in weaker soil conditions.
4. Earthquake Resistance
   In earthquake-prone areas, pile caps firmly connect the piles, maintaining foundation stability during seismic events.
5. Improve Building Foundation
   Pile caps play a vital role in ensuring a well-constructed foundation beneath the structure. They provide a solid support for the long-lasting stability of the entire structure.

Conclusion
Pile caps are essential structural components that secure the foundation. They are critical for bearing the load and enhancing stability. Without pile caps, the foundation of high-rise buildings may be weakened, posing future risks.