Deep Foundation

Contents

**Recall the necessity of the Pile Foundation** 2

**Describe the Driven Cast-in-Situ concrete Piles** 4

**Recall the concept of Negative Skin Friction** 5

**Describe Under-Reamed Piles in the Clay** 6

**Recall Dynamic Formula for the Driven Piles** 8

**Recall the concept of Group Action of Piles** 9

**Recall the efficiency of the Group of Piles** 11

**Describe Pile-Groups in Sand, Gravels, and Clay** 12

**Recall Settlement of the Pile Group** 14

**Describe Sharing of Loads in the Pile Group** 15

**Define the term Pile**

A pile is a long, cylindrical, and vertical foundation member used to transfer the load from a structure to a deeper and stronger soil layer. It is commonly used in situations where the surface soil is not strong enough to support the weight of a building or structure. Piles can be made from various materials such as concrete, steel, timber, or a combination of these materials.

The term pile is also used to refer to a group of similar elements driven into the ground for the purpose of supporting a structure. The piles are typically spaced at regular intervals and connected to the structure by a cap or a beam.

In summary, a pile is a long and narrow foundation element used to transfer the load of a structure to a deeper and stronger soil layer. It is commonly used in situations where the surface soil is not adequate to support the weight of a building or structure.

**Recall the necessity of the Pile Foundation**

Pile foundation is necessary in situations where the surface soil is not strong enough to support the weight of a building or structure. This is often the case in areas where the soil is soft, marshy, or prone to settlement. In such situations, pile foundations are used to transfer the load of the structure to a deeper and stronger soil layer.

Another situation where pile foundations are necessary is when a structure needs to be built on an unstable soil layer, such as an area prone to landslides or erosion. Piles can be used to stabilize the soil and prevent movement of the structure.

In addition, pile foundations are also used in areas with high water tables or areas that are prone to flooding. Piles can be driven into the ground to a depth below the water table to prevent the structure from floating or being damaged by water.

Finally, pile foundations are also used in areas where the soil is unable to support the heavy loads from large structures such as bridges, offshore platforms, or tall buildings.

In summary, pile foundations are necessary in situations where the surface soil is not strong enough to support the weight of a structure, in areas prone to landslides or erosion, in areas with high water tables, and in areas where the soil is unable to support heavy loads from large structures.

**Classify the Pile**

Piles can be classified into several types based on their materials, method of installation, and shape. Some of the common classifications of piles are:

- Based on Material: Concrete piles, Steel piles, Timber piles, and Composite piles (made from a combination of materials)
- Based on Installation method: Driven piles (installed by impact or vibration), Bored piles (installed by drilling), Screw piles (installed by rotating into the ground), and Jetted piles (installed by high-pressure water)
- Based on Shape: Round piles, Square piles, Rectangular piles, and H-piles (shaped like the letter H)
- Based Function: End-bearing piles (transfer load to a bearing stratum), Friction piles (transfer load by skin friction), and Compression piles (designed to resist compressive loads)
- Based on Load-transfer mechanism: Bearing piles (transfer load through end-bearing), Friction piles (transfer load through skin friction), and Expansion piles (expand in the ground to transfer load)

These are some of the common classifications of piles. Understanding the different types of piles and their functions is important in choosing the right type of pile for a specific project.

In summary, piles can be classified based on their materials, method of installation, shape, function, and load-transfer mechanism. Some of the common types are concrete, steel, timber, and composite piles, driven piles, bored piles, screw piles, and jetted piles, round, square, rectangular, and H-piles, end-bearing, friction, and compression piles, and bearing, friction, and expansion piles.

**Describe the Driven Cast-in-Situ concrete Piles**

Driven Cast-in-Situ concrete piles are a type of pile foundation used to transfer the load of a structure to a deeper and stronger soil layer. As the name suggests, these piles are made from concrete and are cast in place, which means that the concrete is poured into the pile form while it is being driven into the ground.

The piles are usually cylindrical in shape and are installed using a pile driver. The pile driver is a machine that delivers repetitive blows to the top of the pile to drive it into the ground. The pile is driven until it reaches the desired depth or until it encounters a bearing stratum that can support the load of the structure.

The advantage of driven cast-in-situ concrete piles is that they are very strong and can support heavy loads. They are also very versatile and can be used in a variety of soil conditions, including hard, rocky soils and soft, marshy soils.

However, the installation process can be noisy and disruptive, and it requires specialised equipment and skilled labour. Additionally, the concrete in the pile needs to cure for several days before the pile can be used to support the structure.

In summary, driven cast-in-situ concrete piles are a type of pile foundation made from concrete and installed using a pile driver. They are strong and versatile but can be noisy and disruptive to install, and the concrete in the pile needs time to cure before it can be used to support the structure.

**Describe Static Methods for the following: i. Driven Piles in Sand ii. Driven Piles in Saturated Clay iii. For Bored Piles**

Static methods are techniques used to determine the load-bearing capacity of piles. There are several static methods that can be used to determine the load-bearing capacity of driven piles in sand, driven piles in saturated clay, and bored piles.

i. Driven piles in sand: One of the common methods used to determine the load-bearing capacity of driven piles in sand is the Static Load Test. In this method, a load is applied to the pile and the resulting settlement is measured. The load-bearing capacity of the pile can be determined from the load-settlement curve. Another method used for driven piles in sand is the SPT (Standard Penetration Test) value. The SPT value is a measure of the energy required to drive a standard sampler into the soil, and it can be used to estimate the load-bearing capacity of driven piles in sand.

ii. Driven piles in saturated clay: To determine the load-bearing capacity of driven piles in saturated clay, the Plate Load Test or the Static Load Test can be used. In the Plate Load Test, a circular plate is placed on the ground and a load is applied to the center of the plate. The resulting settlement of the plate is measured, and the load-bearing capacity of the pile can be determined from the load-settlement curve. The Static Load Test is similar to the Plate Load Test, but the load is applied directly to the pile.

iii. Bored piles: To determine the load-bearing capacity of bored piles, the Static Load Test is commonly used. In this method, a load is applied to the pile and the resulting settlement is measured. The load-bearing capacity of the pile can be determined from the load-settlement curve. Another method used for bored piles is the Pile Integrity Test, where a low-frequency signal is introduced into the pile, and the response of the pile is measured to determine the integrity of the pile.

In summary, there are several static methods that can be used to determine the load-bearing capacity of driven piles in sand, driven piles in saturated clay, and bored piles. Some of the common methods are the Static Load Test, Plate Load Test, SPT, and Pile Integrity Test. These methods help to ensure that the piles have the capacity to support the load of the structure and prevent structural failure.

** ****Recall the concept of Negative Skin Friction**

Negative skin friction is a phenomenon that occurs in piles that are installed in soils with low friction. It occurs when the soil around the pile is unable to support the weight of the pile and the load it carries, resulting in the soil sliding along the surface of the pile. This can lead to a reduction in the load-bearing capacity of the pile and increased settlement of the pile and the structure it supports.

Negative skin friction is most commonly encountered in sands and gravels and in soft clays. The negative skin friction is caused by the downward flow of soil grains along the surface of the pile, resulting in a reduction in the soil’s ability to support the weight of the pile. This can lead to a reduction in the load-bearing capacity of the pile and increased settlement.

To mitigate negative skin friction, pile design should consider the soil conditions and the anticipated magnitude of negative skin friction. This can be done by using larger diameter piles, increasing the depth of the pile, or increasing the weight of the pile. Additionally, the pile can be coated with a material, such as grout or bitumen, to reduce soil migration along the surface of the pile.

In summary, negative skin friction is a phenomenon that occurs when the soil around a pile is unable to support the weight of the pile and the load it carries, resulting in soil sliding along the surface of the pile. This can lead to a reduction in the load-bearing capacity of the pile and increased settlement. The pile design should consider the soil conditions and the anticipated magnitude of negative skin friction to mitigate its effects.

**Describe Under-Reamed Piles in the Clay**

- Under-Reamed Piles in Clay:

Definition: Under-Reamed piles are foundation piles that have an enlarged base section at the bottom, which is called the under-ream. The under-ream provides stability and resistance to lateral forces by increasing the bearing area and spreading the load over a larger area.

Advantages: Under-reamed piles have several advantages, including:

a. Improved stability due to increased bearing area and load spreading.

b. Increased resistance to lateral forces, which makes them ideal for use in soft or unstable soil conditions.

c. Reduced risk of failure due to the increased capacity of the piles to resist axial and lateral loads.

Construction process: The construction process of under-reamed piles involves the following steps:

a. Drilling a hole to the required depth using a rotary drill rig.

b. Installing a temporary casing to prevent soil collapse and maintain the stability of the hole.

c. Expanding the under-ream using a reaming tool, which is attached to the drill rig.

d. Removing the casing and filling the under-realm with concrete.

Installing reinforcement and casting the pile cap.

Design considerations: When designing under-reamed piles, the following factors should be considered:

a. Load capacity: The load capacity of the piles should be determined based on soil strength and pile geometry.

b. Spacing: The spacing of the piles should be determined based on the load capacity and the required stability.

c. Diameter: The diameter of the piles should be determined based on the load capacity and the required stability.

d. Depth: The depth of the piles should be determined based on the soil conditions and the required stability.

Applications: Under-reamed piles are commonly used in the following applications:

a. Buildings and structures in soft or unstable soil conditions.

b. Bridges and viaducts.

**Recall Dynamic Formula for the Driven Piles
**

Dynamic Formula for Driven Piles:

- Definition: The dynamic formula for driven piles is an empirical equation that is used to estimate the ultimate capacity of driven piles based on their dynamic response during installation.

Formula: The dynamic formula is usually expressed as:

- Q = C N A (S / W)
^{(1/2)}

Where:

Q = Ultimate pile capacity (kN)

C = Dynamic pile factor (dimensionless)

N = Number of blows per unit length of pile (blows/m)

A = Cross-sectional area of pile (m^{2})

S = Energy per blow (N-m)

W = Unit weight of soil (kN/m^{3})

- Dynamic pile factor (C): The dynamic pile factor (C) represents the energy transfer efficiency from the hammer to the pile, and it is usually determined from test piles or from a database of previous test results.
- Number of blows per unit length of pile (N): The number of blows per unit length of pile (N) is a measure of the energy input into the pile during installation. It is determined based on the hammer energy and the pile driving conditions.
- Energy per blow (S): The energy per blow (S) is a measure of the energy delivered by the hammer to the pile during each blow. It is determined based on the hammer type, weight, and velocity.
- Cross-sectional area of pile (A): The cross-sectional area of pile (A) represents the area of the pile that is in contact with the soil. It is used to calculate the pile capacity based on the soil strength.
- Unit weight of soil (W): The unit weight of soil (W) is a measure of the soil density and it is used to calculate the pile capacity based on the soil strength.
- Applications: The dynamic formula for driven piles is widely used in the design and construction of driven pile foundations for buildings, bridges, and other structures. It is a valuable tool for engineers and contractors to estimate the capacity of driven piles and to optimize the pile driving process.

**Recall the concept of Group Action of Piles**

- Group Action of Piles:Definition: Group action of piles refers to the behaviour of a group of piles when they are installed and loaded together as a foundation system.

Benefits: Group action of piles can provide several benefits, including:

a. Increased stability due to the interaction between the piles, which results in a more uniform distribution of load and a reduction in the risk of failure.

b. Increased efficiency in terms of the number and size of piles required, which can lead to reduced construction costs and improved construction schedules.

c. Improved load-carrying capacity, which is especially important in areas with weak or compressible soil.

Factors affecting group action: The behaviour of a group of piles is influenced by several factors, including:

a. Soil conditions: Soil conditions, such as soil strength, soil type, and soil moisture, affect the load-carrying capacity and the distribution of loads within the group of piles.

b. Spacing: The spacing between piles affects the distribution of loads and the stability of the group of piles.

c. Orientation: The orientation of the piles affects the distribution of loads and the stability of the group of piles.

d. Number of piles: The number of piles in the group affects the load-carrying capacity and the stability of the group.

Design considerations: When designing a foundation system using group action of piles, the following factors should be considered:

a. Load capacity: The load capacity of the piles should be determined based on soil strength, pile geometry, and the design load.

b. Spacing: The spacing between piles should be determined based on the load capacity and the required stability.

c. Orientation: The orientation of the piles should be determined based on the load capacity and the required stability.

d. Number of piles: The number of piles should be determined based on the load capacity and the required stability.

Applications: Group action of piles is commonly used in the construction of foundation systems for buildings, bridges, and other structures, especially in areas with weak or compressible soil. The concept of group action is also useful for the design and construction of retaining walls, embankments, and slopes.

**Recall the efficiency of the Group of Piles**

Efficiency of Group of Piles:

- Definition: The efficiency of a group of piles refers to the ability of the group to transfer loads to the soil and support the applied loads with minimum deformations.

Factors affecting efficiency: The efficiency of a group of piles is affected by several factors, including:

a. Soil conditions: Soil conditions, such as soil strength, soil type, and soil moisture, affect the load-carrying capacity and the distribution of loads within the group of piles.

b. Spacing: The spacing between piles affects the distribution of loads and the stability of the group of piles.

c. Orientation: The orientation of the piles affects the distribution of loads and the stability of the group of piles.

d. Number of piles: The number of piles in the group affects the load-carrying capacity and the stability of the group of piles.

- Load-carrying capacity: The load-carrying capacity of a group of piles is a function of the soil strength, pile geometry, and the number of piles in the group.
- Load distribution: The load distribution within a group of piles is affected by the spacing, orientation, and number of piles in the group. A more uniform distribution of loads can lead to increased efficiency and stability.
- Deformations: The deformations of a group of piles are a measure of the displacements and settlements that occur under the applied loads. A group of piles with low deformations is considered to be more efficient.

Design considerations: When designing a foundation system using a group of piles, the following factors should be considered to ensure maximum efficiency:

a. Load capacity: The load capacity of the piles should be determined based on soil strength, pile geometry, and the design load.

b. Spacing: The spacing between piles should be determined based on the load capacity and the required stability.

c. Orientation: The orientation of the piles should be determined based on the load capacity and the required stability.

d. Number of piles: The number of piles should be determined based on the load capacity and the required stability.

- Applications: The efficiency of a group of piles is an important consideration in the design and construction of foundation systems for buildings, bridges, and other structures, especially in areas with weak or compressible soil. The efficiency of a group of piles can also be used to optimize the design and construction of retaining walls, embankments, and slopes.

**Describe Pile-Groups in Sand, Gravels, and Clay**

Pile-Groups in Sand, Gravels, and Clay:

- Definition: Pile-groups are a type of foundation system consisting of multiple piles that are installed in the ground and connected to transfer loads from the structure to the soil. Pile-groups can be found in various soil types, including sand, gravels, and clay.
- Sand: In sand, pile-groups are commonly used for shallow foundations, where the soil is not strong enough to support the loads from the structure. Pile-groups in sand are usually installed in a dense pattern to ensure that the loads are distributed evenly and the piles are stable.
- Gravels: In gravels, pile-groups can be used for both shallow and deep foundations, depending on the strength and stability of the soil. Pile-groups in gravels can be installed in a more open pattern than in sand, as the soil is stronger and can support more load.
- Clay: In clay, pile-groups are typically used for deep foundations, where the soil is not strong enough to support the loads from the structure. Pile-groups in clay are usually installed in a dense pattern to ensure that the loads are distributed evenly and the piles are stable. The type of pile used in clay should be selected based on the soil strength and the load capacity required.
- Load capacity: The load capacity of pile-groups in sand, gravels, and clay is dependent on several factors, including the soil strength, pile geometry, and the number of piles in the group. The pile-group design should consider the soil conditions and the loads that the structure will be subjected to.
- Load distribution: The load distribution within a pile-group is affected by the spacing, orientation, and number of piles in the group. A more uniform distribution of loads can lead to increased efficiency and stability.
- Deformations: The deformations of a pile-group are a measure of the displacements and settlements that occur under the applied loads. The deformations of a pile-group in sand, gravels, and clay are dependent on several factors, including the soil strength, pile geometry, and the number of piles in the group.

Design considerations: When designing a foundation system using a pile-group, the following factors should be considered to ensure maximum efficiency:

a. Soil conditions: The soil conditions, including the soil type and strength, should be considered when selecting the type of pile and the spacing and orientation of the piles in the group.

b. Load capacity: The load capacity of the piles should be determined based on soil strength, pile geometry, and the design load.

c. Spacing: The spacing between piles should be determined based on the load capacity and the required stability.

d. Orientation: The orientation of the piles should be determined based on the load capacity and the required stability.

e. Number of piles: The number of piles should be determined based on the load capacity and the required stability.

- Applications: The use of pile-groups as a foundation system is common in areas with weak or compressible soil, such as sand, gravels, and clay. Pile-groups are used for a wide range of structures, including buildings, bridges, and retaining walls, to provide a stable and efficient foundation.

**Recall Settlement of the Pile Group**

- Understanding pile settlements: Pile settlements are changes in the vertical position of the pile foundation due to the applied loads, soil deformation and/or consolidation.
- Types of pile settlements: There are two main types of pile settlements: immediate and long-term settlements. Immediate settlements occur immediately after the piles are installed, while long-term settlements occur over a period of time.
- Causes of pile settlements: The causes of pile settlements include the compression of soil around the piles, the compression of soil in the piles themselves, and the redistribution of loads between the piles and the soil.
- Factors affecting pile settlements: The factors affecting pile settlements include the type of soil, the depth of the piles, the load on the piles, the pile diameter, and the pile spacing.
- Measuring pile settlements: Pile settlements can be measured using various techniques, including inclinometers, settlement plates, and tilt meters.
- Importance of monitoring pile settlements: Monitoring pile settlements is important in order to determine if the piles are settling at an acceptable rate, and to identify any potential problems before they become serious.
- Mitigating pile settlements: The methods for mitigating pile settlements include increasing the size of the piles, reducing the load on the piles, or increasing the pile spacing.
- Importance of proper design and construction of pile foundations: Proper design and construction of pile foundations is critical in order to ensure that pile settlements are minimised and the pile foundation performs as intended.

**Describe Sharing of Loads in the Pile Group**

- Understanding the concept of load sharing in pile groups: Load sharing refers to the distribution of loads between the individual piles in a pile group. It is a crucial aspect of pile foundation design, as it affects the stability, performance, and longevity of the structure.
- Load sharing mechanisms in pile groups: Load sharing in pile groups occurs through two main mechanisms: point load transfer and distribution of lateral loads. Point load transfer occurs when the load is transferred directly from the structure to a single pile. Lateral load distribution occurs when the load is shared by multiple piles.
- Factors affecting load sharing in pile groups: Factors affecting load sharing in pile groups include the spacing between piles, the type of soil, the orientation of the piles, and the load capacity of each pile.
- Importance of proper design and spacing of piles in load sharing: Proper design and spacing of piles is crucial in ensuring that the loads are shared effectively between the piles. This helps to prevent overloading of individual piles, reducing the risk of failure and ensuring the stability of the structure.
- Load transfer at pile-soil interface: Load transfer at the pile-soil interface is a critical factor in determining the load-sharing mechanism in pile groups. The pile-soil interaction must be properly understood and accounted for in the design to ensure effective load transfer and proper distribution of loads in the pile group.
- Load distribution in pile groups with different pile configurations: Different pile configurations, such as pile groups with a common pile cap or groups with different pile spacings, can affect the load distribution in the pile group. It is important to consider these different configurations in the design and analysis of pile foundations.
- Importance of load testing in pile groups: Load testing is an important tool for verifying the load-sharing capabilities of pile groups. This helps to validate the design and ensure that the piles are capable of carrying the expected loads.
- Importance of monitoring load sharing in pile groups: Monitoring load sharing in pile groups is important to ensure that the piles are performing as intended and that the loads are being shared effectively. This helps to identify any potential issues early, reducing the risk of failure and ensuring the longevity of the structure.