Types of Piles for Pile Foundation Based on Load Transfer and Function
Piles are a common type of foundation used in construction to support structures and transfer loads to the ground. Piles can be classified based on their load transmission and functional behavior.
One classification is end bearing piles, also known as point bearing piles. These piles are designed to transfer loads from the structure to a strong bearing stratum or rock layer located deep in the ground. End bearing piles are typically used in structures with heavy vertical loads and are driven deep into the ground to ensure that they reach the bearing stratum.
Another classification is friction piles, also known as cohesion piles. These piles rely on the friction between the pile and the surrounding soil to transfer the load to the ground. Friction piles are commonly used in structures that experience lateral loads or when the bearing stratum is not located at a sufficient depth. The length of the pile is important in friction piles as longer piles generate more friction and can transfer more load.
Finally, there are piles that combine both friction and cohesion elements. These combination piles are used in situations where the soil conditions are mixed and require both types of load transmission. The type of pile used in a construction project will depend on several factors, including the type of structure, soil conditions, and load requirements.
End bearing piles
Piles are structures that transfer their load onto a firm layer deep below the structure’s base. Their ability to bear the load mainly depends on the resistance of the soil at the pile’s toe. Piles behave like regular columns, and their design should be approached accordingly. Buckling is not a concern for piles, even in weak soil, unless part of the pile is unsupported in either air or water. The soil’s load-bearing capacity is transmitted to the pile through friction or cohesion.
However, the soil surrounding the pile may stick to the pile’s surface, causing “Negative Skin Friction,” which can significantly affect the pile’s capacity. Negative skin friction occurs due to the drainage of ground water and soil consolidation. The depth at which the pile is founded depends on the results of the site investigation and soil testing.
Friction or cohesion piles
The capacity of a pile to support weight is determined primarily by the adhesion or friction between the soil and the pile shaft. Figure 2 illustrates this relationship. The ability of the soil to adhere to the pile or offer resistance to its movement is what provides the pile with its load-bearing capacity.
Without sufficient adhesion or friction, the pile may fail to support the weight it was designed to carry, resulting in structural damage or collapse. Therefore, it is crucial to consider the soil conditions when designing and installing piles to ensure they can adequately support the intended load.
By analyzing the soil properties and selecting appropriate pile types and installation methods, engineers can determine the optimal carrying capacity for a given site. This information is essential for ensuring the safety and stability of structures built on top of piles, such as buildings, bridges, and other infrastructure.
Figure 1: End bearing piles
Figure 2: Friction or cohesion pile
The type of piles being referred to here primarily rely on skin friction to transfer their load to the soil. These piles are often driven into the ground in groups, which can lead to a reduction in the porosity and compressibility of the soil within and around the group. As a result, they are sometimes called compaction piles.
However, during the process of driving these piles into the ground, the soil can become molded and lose some of its strength. This means that the pile may not be able to transfer the exact amount of load that it was intended to immediately after being driven. It typically takes around three to five months for the soil to regain some of its strength.
These piles are also known as cohesion piles.
Friction piles
Pile foundations are a type of foundation used in construction to transfer loads from a structure to the ground. In some cases, piles are driven into the ground to provide support for the structure. These piles rely on the soil’s ability to resist the load and transfer it to the ground through a process called skin friction.
One type of pile foundation that relies on skin friction is called a floating pile foundation. This type of foundation is used when the soil is too soft or too weak to support the structure’s weight. Instead of compacting the soil during installation, these piles rely on the friction between the pile and the soil to transfer the load to the ground. This results in minimal soil compaction and is an effective solution for soft or weak soils.
Combination of friction piles and cohesion piles
only given context in paragrahs
The end bearing pile can be extended when the stratum where it is to be placed is not hard, such as firm clay. In such cases, the pile is driven deep enough into the lower layer to develop enough frictional resistance. This is done to ensure that the pile can still effectively bear the load placed upon it, despite the softer ground.
An alternative to this method is to use piles with enlarged bearing areas. This is achieved by forcing a bulb of concrete into the soft stratum immediately above the firm layer. This creates a wider base for the pile, which provides increased stability and load-bearing capacity. In the case of bored piles, a similar effect can be achieved by forming a large cone or bell at the bottom using a special reaming tool.
Piles with enlarged bearing areas have several advantages over traditional piles. They have higher tensile strength and can be used as tension piles. This means that they can resist forces pulling them out of the ground, in addition to bearing loads placed upon them. Additionally, the wider base of these piles can distribute the load more evenly, reducing the likelihood of settlement or failure.
Figure 3: Under Reamed base enlargement to a bore-and-cast-in-situ pile
Classification of pile with respect to type of material
Piles are structural elements that are commonly made from different materials, such as timber, concrete, steel, and composite materials. Timber is a popular choice for temporary piles and when it is available at an affordable price. Concrete, on the other hand, is commonly used for precast, cast-in-place, and prestressed piles. Steel piles are typically utilized for permanent or temporary works.
Timber piles can be made from different species of wood, such as spruce, pine, or fir, and are generally used for short-term applications, such as in temporary structures, cofferdams, and bridges. Concrete piles, on the other hand, are known for their durability and strength and can withstand high compressive loads. They are ideal for use in permanent structures such as bridges, wharves, and industrial buildings.
Steel piles are often used when high strength and durability are required, such as in marine structures and deep foundations. They can be driven into the ground, making them suitable for a wide range of soil conditions. Composite piles, which are a combination of two or more materials, are gaining popularity due to their high strength and versatility. They can be made from a combination of materials such as steel and concrete or timber and fiberglass, depending on the specific requirements of the project.
Timber piles
Timber has been utilized as a building material for centuries, and it remains a popular choice for permanent structures in areas where it is readily available. Timber is especially well-suited for long cohesion piling and piling beneath embankments. However, it is crucial that the timber used is in good condition and has not been attacked by insects.
For timber piles that are less than 14 meters in length, the tip diameter should be larger than 150 mm. If the length is greater than 18 meters, a tip with a diameter of 125 mm is acceptable. It is vital to drive the timber in the correct direction and not to drive it into firm ground as this can easily damage the pile.
To protect the timber against decay and putrefaction, it is essential to keep it below the groundwater level. Toe covers can be used to protect and strengthen the tip of the pile. Pressure creosoting is the standard method for protecting timber piles.
Advantages and disadvantages of Wood piles
Piles are a popular choice for foundations due to their easy handling, relatively low cost in areas with abundant timber, and the ability to join sections together and remove excess length as needed. However, there are also some drawbacks to using piles as a foundation. One of these is that the piles are susceptible to rotting above the ground water level, which can compromise their structural integrity. Additionally, piles have a limited bearing capacity, which can be problematic in certain situations.
Another issue with using piles is that they are vulnerable to damage during the driving process, particularly if there are stones or boulders present in the soil. This can lead to structural issues or even the need to replace damaged piles entirely. Finally, piles can be difficult to splice together, which can make repairs more challenging, and they are also susceptible to damage from marine borers in salt water environments.
Overall, while piles can be a practical and cost-effective option for certain foundation needs, it’s important to weigh the pros and cons carefully before deciding whether they are the right choice for a particular project. Factors like the soil and water conditions, the presence of potential hazards like stones or marine borers, and the required bearing capacity will all need to be taken into account.
Concrete piles
There are two types of concrete piles: precast and cast in place. Precast concrete piles are manufactured off-site and then transported to the construction site where they are installed. Cast in place concrete piles, on the other hand, are made on-site by pouring concrete into a hole or shaft that has been drilled or bored into the ground. Both types of concrete piles are commonly used in construction and are designed to provide support and stability to buildings and other structures.
Precast concrete Piles or Prefabricated concrete piles
High-quality controlled concrete is utilized to form and reinforce piles that are commonly used in square, triangle, circle, or octagonal sections. These piles are produced in short lengths of one-meter intervals, ranging from 3 to 13 meters. The precast nature of these piles makes it easy to connect them together to attain the desired length without compromising their load-bearing capacity.
To withstand handling and driving stresses, reinforcement is necessary within the pile. Moreover, prestressed concrete piles are becoming increasingly popular as they require less reinforcement than ordinary precast piles. The use of prestressed concrete piles helps reduce the amount of reinforcement needed while still maintaining the load capacity of the pile.
Figure 4:a) concrete pile connecting detail. b) squared precast concrete pile
The pile joint known as the Hercules type, as depicted in Figure 5, boasts several advantages. Firstly, it can be cast into the pile with ease and precision, ensuring accurate dimensional tolerances. Moreover, it can be swiftly and safely assembled on site. This is made possible by its construction from high-grade steels.
Figure-5: Hercules type of pile joint
Advantages and disadvantages of Precast concrete Piles
Pile materials that are stable in squeezing ground, such as soft clays, silts, and peats, have some advantages when it comes to piling. One benefit is that the pile material can be inspected before piling, which can help ensure the stability of the foundation. In addition, these materials are relatively easy to splice and are generally less expensive than other types of pile materials. They can also be driven in long lengths, which can be useful in certain situations. Finally, using these types of piles can help increase the relative density of a granular founding stratum.
However, there are also some disadvantages to using these types of piles. One potential problem is that the displacement, heave, and disturbance of the soil during driving can be significant. This can lead to damage to the piles during driving, which may require replacement. In addition, these piles cannot be driven with very large diameters or in conditions where there is limited headroom. Despite these disadvantages, using stable pile materials in squeezing ground can be an effective way to provide a stable foundation for a variety of structures.
Cast in place Concrete piles
Cast in place concrete piles are a popular choice for foundation construction due to their versatility and ability to be introduced into soil. However, issues such as arching, squeezing, and segregation may arise during the implementation of these piles. Two common types of cast in place concrete piles are driving and drilling piles.
Piles poured in tubes with underneath heels and left when lifting the tubes are a type of cast in place concrete pile. The simplex pile is an example of this type, with a 40 cm diameter tube and an underneath heel. It is banged underground by an automatic hammer until reaching the arable land for establishment, then concrete is poured and the tube is raised to prevent soil from entering. This pile can support up to 40-50 tons. The Frankie pile is another example, with multiple tubes nested inside each other for easy access to greater depths. A reinforced concrete heel may be used and left in the ground to prevent the entry of cold water pipes. This pile can support loads of 50-80 tons.
Vibro pile is a type of cast in place concrete pile made from a 40 cm diameter steel pipe with a conical heel and separate flange. It is banged underground by an automatic hammer until reaching arable land, then the heel is removed and the pipe is placed in a tube. Concrete is poured and the tube is moved up and down approximately 80 times per minute to compact the concrete. This pile can support up to 60 tons. The strong pile is similar to the simplex pile but has a reinforced concrete bottom heel covered with cast heel. This pile can support loads of 25-30 tons.
Piles with open tubes without heel are also a type of cast in place concrete pile. The Strauss pile is an example, similar to the simplex pile but without a heel. Soil can be removed from the tubes by special devices, and concrete is poured in its place. The maximum load that can be carried by these piles is 20-25 tons. The Kimbersol pile is created by digging a well with a diameter of approximately 80 cm until reaching arable land, then compacting the bottom of the well with a rounded hammer and filling it with concrete. This pile can support loads of 80-120 tons.
The Welfchaulzer pile involves banging a 30-40 cm diameter pipe until reaching arable land, removing the inside soil, placing steel bars, covering the opened upper hole tightly and leaving holes to connect the compressed air so that leachates can be expelled, and pouring concrete with a ratio of 1:4. The Raymond pile consists of cylindrical chips with diameters of 40-60 cm at the top and 20-28 cm at the bottom. It is banged inside by a mandrill and the cylindrical chips are left in the soil and filled with concrete.
Advantages and disadvantages of cast-in-place concrete piles
Precast concrete piles offer several advantages over other types of foundation piles. One major benefit is that they can be inspected prior to casting and easily cut or extended to the desired length. They are also relatively inexpensive, and the piles can be cast before excavation. The length of the piles is adjustable, and an enlarged base can be formed to increase the relative density of the granular founding stratum, leading to a higher end bearing capacity. Furthermore, reinforcement is not affected by handling or driving stresses.
However, there are some potential drawbacks to using precast concrete piles. The heave of the neighboring ground surface can cause reconsolidation and the development of negative skin friction forces on the piles. There is also a risk of tensile damage to unreinforced piles or those made of green concrete, where forces at the toe are strong enough to resist upward movement. Additionally, thinly cased or uncased green concrete piles can be damaged by lateral forces in the soil, and concrete may be weakened if artesian flow pipes up the shaft of the piles when the tube is removed. Light steel sections or precast concrete shells may also be damaged or distorted by hard driving. Furthermore, precast concrete piles cannot be driven where there is limited headroom, and installation is time-consuming, as they cannot be used immediately after installation. Lastly, their length is limited.
Bored and cast-in-place (non-displacement piles)
Piles have several advantages when it comes to adapting to different soil conditions. One such advantage is their ability to vary in length according to the ground conditions they encounter. Additionally, piles can be installed in large diameters, making them a useful option for projects that require a strong foundation. In clays, end enlargement up to two or three diameters are possible, further increasing their adaptability. Furthermore, the material used for the piles is not dependent on the handling or driving conditions, providing a greater degree of flexibility in their use. Finally, piles can be installed to great lengths, which is particularly useful for projects that require a deep foundation.
However, there are some disadvantages to using concrete piles. One issue is that concrete cannot be placed under ideal conditions and is difficult to inspect after it has been installed. Additionally, water under artesian pressure may pipe up the pile shaft, washing out the cement and potentially compromising the integrity of the structure. Another drawback is that concrete piles are difficult to extend above ground level, which can be a problem for river and marine structures. Finally, when using boring methods to install piles in sandy or gravelly soils, the soil may become loose and require grouting to achieve a more economical base resistance.
Steel piles
Steel piles are commonly used in construction and are available in different shapes, including sectors in the form of H, X or thick pipes. Due to their high strength and relatively small cross-sectional area, they are suitable for driving in long lengths and penetrating firm soil easily. Steel piles can also be easily cut or joined by welding, making them a versatile option for construction projects.
However, when steel piles are driven into soil with a low pH value, there is a risk of corrosion. To address this issue, tar coating or cathodic protection can be employed in permanent works. Additionally, designers may choose to over-dimension the cross-sectional area of the steel pile to account for potential corrosion. By doing so, the corrosion process can be prolonged for up to 50 years.
The speed of corrosion for steel piles is typically 0.2-0.5 mm/year, but in design, this value can be taken as 1mm/year. Despite the risk of corrosion, steel piles remain a popular choice in construction due to their strength and versatility.
Figure 6: Steel piles cross-sections
Advantages and disadvantages of Steel piles
Piles offer several advantages as foundation elements. They are manageable and can be conveniently cut to the required length. Additionally, they can be driven through compacted layers and create minimal soil displacement, especially when using steel section H or I section piles. Moreover, these piles can be spliced or bolted together with relative ease, and they can withstand high driving forces and extended lengths, allowing for heavy loads to be supported.
However, piles also have a few disadvantages. Firstly, they are susceptible to corrosion over time. Secondly, they can deviate from their intended path during driving, leading to difficulties in achieving the desired vertical alignment. Lastly, piles tend to be relatively expensive compared to other foundation options.
Composite piles
In order to protect timber piles from decay and insect attack, a common practice is to use a combination of different materials in the same pile. When a timber pile is installed above the ground water level, it is vulnerable to these types of damage. To avoid this, concrete or steel piles are used in place of timber above the ground water level. By contrast, timber piles are suitable for installation under the ground water level.
This approach is illustrated in figure 7, where a combination of different materials is used in a single pile. Specifically, a timber pile is installed under the ground water level, while a concrete or steel pile is used above it. This configuration allows for the benefits of both materials to be utilized while mitigating their respective weaknesses. The timber pile can resist compressive loads and is cost-effective, while the concrete or steel pile provides protection against decay and insect attack.
Figure 7: Protecting timber piles from decay
The given context can be rewritten into two separate paragraphs as follows:
a) Precast concrete upper section above water level: One way to protect underwater structures is to use precast concrete for the upper section above the water level. This involves casting the concrete on land and then transporting it to the site to be installed on top of the underwater structure. By using precast concrete, the construction time can be reduced and the quality can be ensured, as the concrete can be produced under controlled conditions in a factory. Additionally, the precast concrete can be designed to fit the specific requirements of the underwater structure, providing a custom solution that is both durable and efficient.
b) Extending pile cap below water level: Another way to protect underwater structures is to extend the pile cap below the water level. The pile cap is the part of the foundation that sits on top of the piles and transfers the load of the structure to the foundation. By extending the pile cap below the water level, the piles are protected from erosion and corrosion, which can cause structural damage. This method requires careful planning and execution to ensure that the pile cap is securely attached to the piles and that the underwater environment is taken into consideration during the construction process. However, it can provide a reliable and cost-effective solution for protecting underwater structures.
Classification of pile with respect to effect on the soil
In construction projects involving deep foundations, such as high-rise buildings or bridges, piles are often used to support the weight of the structure. Piles are long, cylindrical columns made of concrete or steel that are driven deep into the ground to provide a stable foundation. One way to categorize piles is to divide them into two types: driven piles and bored piles. This classification is based on the method used to install the piles.
Driven piles are installed by using a pile driver, which is a machine that hammers the pile into the ground. The hammering action of the pile driver generates a large amount of force, which helps to compact the soil around the pile and provide additional support. Driven piles are commonly used in projects where the soil conditions are relatively firm and stable.
Bored piles, on the other hand, are created by drilling a hole into the ground and then filling it with concrete or another material. This method is typically used in projects where the soil conditions are softer or more unstable, as it allows for greater control over the installation process. Bored piles are also used in situations where the noise and vibration associated with pile driving would be disruptive to nearby buildings or structures.
Overall, the classification of piles into driven or bored provides a simplified way to understand the different types of foundation support systems used in construction projects. By knowing the characteristics and advantages of each type of pile, engineers and contractors can select the most appropriate method for a particular project and ensure the stability and safety of the structure.
Driven piles
When it comes to pile foundations, one popular type is the driven pile, which falls under the category of displacement piles. During the installation of a driven pile, the pile shaft is driven into the ground, causing the surrounding soil to move radially. This radial movement occurs as a result of the pile pushing through the soil and displacing it. Additionally, there may be a vertical component of soil movement as the pile enters the ground. The overall effect of the pile driving process is the displacement of soil around the pile shaft, which can provide the necessary support for the foundation.
Figure 8: driven piles
Bored piles
The construction industry makes use of bored piles, also known as replacement piles, which are non-displacement piles produced by boring or excavation. A void is created, and the piles are formed by casting concrete in this space. The process is suitable for stiff clays, as borehole walls do not require additional support. However, unstable ground like gravel needs temporary support, such as casing or bentonite slurry. Alternatively, the casing may be driven into a hole that advances as the casing progresses. Another non-displacement method involves injecting grout or concrete from an auger into granular soil, creating a grouted column of soil. Three non-displacement techniques are used: bored cast-in-place piles, pre-formed piles, and grout or concrete intruded piles. Replacement piles include augered, cable percussion drilling, large-diameter under-reamed, types with precast concrete units, drilled-in tubes, and mini piles.