What is Pile Foundation | Different Types of Pile Foundations | Minimum Pile Foundation Depth
Pile Foundation Design Details | Uses of Pile Foundation | Pile Foundation in Black Cotton Soil | Pile Foundations Advantages and Disadvantages
What is Pile Foundation?
The pile foundation is a type of foundation which is composed of a series of columns, typically made of wood, rock, steel or concrete, that has been driven into the earth below a structure to provide lateral support. It is used in the foundation construction of buildings.
Piles are typically driven into the ground until their tops are at the same elevation as the building’s footings, or below the anticipated frost line if present in the area. Piles are also driven to different levels, depending on the height of the structure and other soil conditions.
The soil is typically excavated and removed to a level at or above the anticipated frost line and moisture or water content is usually monitored in the area where piles are to be driven.
A pile foundation is made up of steel, timber, or concrete driven deep into the soil underneath the building to form a triangular, square, or hexagonal pattern.
Piles are usually driven into the soil and compacted to create a sturdy base for the structure to be built. Pile foundations are a dependable form of foundation that have been used for centuries.
Behaving like a series of long, sturdy legs, the foundation will transfer the load of the heavy building to the ground underneath while keeping the building stable.
Generally, foundations provide support to the structure and transfer the weight or loads from the structure to the soil, and therefore the layer at which the foundation transfers the load should have an adequate bearing capacity and suitable settlement characteristics.
Pile Cap Details
A pile cap is a thick concrete pad that is supported by concrete or timber piles placed into soft or unstable ground to create a sufficiently secure foundation.
It is commonly used as part of the deep foundation of a building, usually a multi-story structure or support base for heavy equipment, or of a bridge.
The cast concrete pile cap distributes the building’s load into the piles. A “raft,” which is a concrete foundation floor sitting directly on soft soil prone to subsidence, is a construction comparable to a pile cap.
Pile Cap Design
The mat is made of concrete, a mixture of small rocks and cement. To avoid sagging and fracturing during setting, this combination must be supported by a framework. This is referred to as shuttering and reinforcing.
Long steel bars with longitudinal protrusions between the piles are maintained in shape by thinner tie wires. Following the installation of the steel mat, timber is placed around the perimeter to confine the wet concrete mixture.
When the concrete is poured (typically in a series of tiny loads), it is stirred to remove any air pockets that may undermine the structure when it cures.
As the concrete cures, it undergoes a chemical shift that generates a lot of heat. Pipes conveying refrigerant coolant are sometimes utilized in the mass to assist the setting process and prevent the concrete from breaking if the mass of concrete is very large.
The purpose of a pile cap is to transmit the load of the building into the hard strata of the earth via a pile or set of piles.
The pile cap design employs a truss system idea that can be realized through the use of a strut and tie approach. Designing a pile cap appears to be difficult because several factors must be considered in order to build a secure and sound base.
These factors include the optimum spacing of each pile, the thickness of the pile cap, and so on. This can only be accomplished by knowing its design principles and properly detailing pile caps.
The designer’s issue with pile cap design starts with deciding what proportions or pile cap shape to assume first.
However, determining the correct pile cap proportions might be regarded a half-way point in the design process.
The shape and plan dimensions of the pile cap are determined by the number of piles in the group and the space between them. Pile caps are typically one of different shapes:
- Triangle-shaped (for 3 piles).
- The hexagonal shape (for 6-7 piles).
- Rectangular (for all other number of piles).
A pile cap is often deeper than a comparable pad footing because it is subjected to larger bending moments and shear stresses.
Because of the increased depth, the pile cap captures more stiffness, allowing it to evenly distribute the load to all piles in the group. The following elements influence the depth of the pile cap:
- The pile cap’s shear capacity.
- Ground shrinkage and swelling (particularly in clay soils).
- Anchorage for pilings
- The water table of the ground.
- Frost attack possibility.
Because it is extremely difficult to hole or drive piles precisely vertically, the pile cap should be able to allow some variation in the ultimate position of the pile heads.
Depending on the size of the piles, the pile top should overhang the outer piles by 100-150 mm on both sides.
Pile caps are built by excavating a space around a group of piles to allow formwork to be placed. Trim the pile tops to ensure they are all the same height.
After that, a reinforcing cage is made, positioned in the formwork cast box, and secured to the piles. The concrete is then poured and allowed to cure before the formwork is removed.
Different Types of Pile Foundations in Construction
1. Sheet Pile Foundations
In Sheet pile foundation, the pile is made up of heavy steel bars that can be driven into the ground using a hydraulic hammer or by manual methods.
This is one of the most common types of pile foundation. Similar to a steel tent, this type of foundation can be made with either steel or wood.
This type can go over a wooden sub-structure that is as much as 15 feet deep. The steel or wooden structure creates an airtight enclosure, which adds stability to the entire building, regardless of the weather and soil conditions.
Steel piles are used to support almost three-quarters of a million buildings in the United States alone. They are also used in marine and foundation applications.
Steel piles can be used to construct both vertical and horizontal projects. Steel piles are a common type of pile foundation used for supporting structures on top of the soil.
These Sheets are sections of sheet materials with interlocking edges driven into the ground to provide earth retention and excavation support.
Sheet piles are most commonly made of steel but can also be formed of timber or reinforced concrete. Sheet piles are commonly used for retaining walls, land reclamation underground structures such as car parks and basements in marine locations for riverbank protection, seawalls, cofferdams, etcetera.
2. Cantilever Pile Foundations
Cantilevers are specialized piles used to support structures that would otherwise become unstable from wind or other factors.
A cantilever usually doesn’t rest on the ground, instead, it is supported by the main structure and can be found in a variety of design styles.
3. Helical Pile Foundations
Another common type of piled foundation that is used for marine structures and other applications where there is a high risk of erosion.
Helical piles are installed manually or with the use of hydraulic cylinders, mounted vertically via the use of hydraulic power.
The piles are then twisted, left to right or vice versa, so that the tip of the helical pile can be driven even further into the soil and stay that way by creating a tight friction with the soil.
4. Load Bearing Pile Foundations
As the name suggests, load-bearing piles are used to provide support for structures that have heavyweights.
The pile must be able to withstand the weight by distributing it evenly around the ground in accordance with the soil and weather conditions.
5. End bearing Pile Foundations
Foundations that are built around a wetland area or other waterway can be built using end bearing piles.
In order to prevent flooding, piling is used to keep the structure above water level while keeping it steady.
The end bearing pile is able to withstand the load by leaning against each other and preventing one end of the pile from sinking into the ground.
6. Soil Compactor Pile Foundations
Soil Compactor Piles are piles that are used to stabilize and compact the soil in order to build a foundation.
The piles are constructed by throwing heavy cinder blocks into wet soil, which results in a compacted base.
The soil compactor piles are usually installed during dry weather, but they can be used during wet conditions as well.
7. Friction Pile Foundations
As the name suggests, friction piles are used to keep a structure steady in loose soil conditions.
The pile is usually made up of metal or concrete that is grooved on one side so that it can create a sturdy friction by digging deep into the soil when it is installed.
8. Concrete Pile Foundations
Concrete piles are used mainly for marine applications and other applications where there is a high risk of erosion. These include piers and jetty structures, as well as underwater foundations for bridges and offshore platforms.
9. Driven Piling Foundations
Driven piles are driven or hammered into the ground with the use of vibration. This method of piling is well suited for foundations in non-cohesive soils, ground with a high-water table and for soils that contain contaminates.
Driven piles can be cast in position by using temporary or permanent steel casing. They can also be prepared off site by using pre-cast piles, which can be created using steel, timer, wood, concrete or a combination of these.
10. Screw Pile Foundation
Screw piles are made up of circular hollow galvanized steel pile shafts with one or more steel helices attached to them that are screwed into the ground in the same way that a screw is screwed into wood.
This form of pile reduces the amount of spoil produced during installation and, in some cases, may provide a more sustainable and cost-effective alternative to other approaches.
This type of pile foundation is also known as a helical pile. The screw pile is driven deep into the ground using a helical-shaped head on the end of the pile.
The head is surrounded by a spiral wrap, which threads its way down the length of the screw pile and connects with the drive shaft.
The helical screw piles are used to support structures that are subject to severe soil erosion and other harsh conditions.
11. Bored Pile Foundation
Bored piles are installed by using a machine that is able to bore into the ground and then extract the soil as it creates the circular space.
Once an adequate space has been created, a metal pole or wood is fit into the cavity.
The supporting structure is then built around it.
12. Timber Pile Foundations
Timber piles are the oldest type of piles still in use today. They are typically precast displacement piles erected by drive or, less commonly, vibratory methods. Because of the inherent convergence of pile shafts, we may achieve a reasonably large pile load capacity.
When used correctly, they are a highly cost-effective, efficient, and safe foundation solution for both temporary and permanent constructions.
This is supported by a number of historical structures built on timber piles that have been in use for thousands of years.
Timber piles are mostly used for residential and commercial foundation applications. These include driveways, patios, walls and basement.
13. Cast-in-situ Pile Foundations
Cast-in-situ pile foundations are constructed by drilling holes in the earth to the desired depth. The hole is subsequently filled with concrete. Reinforcements must also be used when needed.
Pile Foundation Design Details
The pile foundation should be designed to withstand both static and cyclic lateral loads. Further, the designer should consider overload scenarios in which the design lateral loads on the platform foundation are augmented by an adequate safety factor.
The designer must be confident that the overall structural foundation system will not break under overloading conditions.
The lateral resistance of the soil at the surface is important in pile design, and the effects of scour and soil disturbance on this resistance during pile installation should be taken into account.
Under lateral stress, clay soils often act as a plastic material, demanding a link between pile-soil deformation and soil resistance.
Driven pile foundations frequently use groups of piles connected by a pile cap (a massive concrete block into which the pile heads are embedded) to distribute weights that are greater than one pile can bear.
To connect the foundation elements, pile caps and isolated piles are commonly connected with grade beams; lighter structural elements bear on the grade beams, while heavier elements bear directly on the pile cap.
Main Uses of Pile Foundation
Pile foundation is the work of erecting or constructing a building on piles which are driven into the ground to provide a stable base to support the weight of the building.
The excavated soil from the hole for the pile is used to fill in the hole around the pile. The load is then transferred to the pile which in turn transfers the load to the ground along a line of bearing.
Pile foundation may also be called a shallow foundation or stem wall or mat. Pile foundation is suitable for use on most soil types, although it is mostly used on uncohesive or loose soil, clay soils, and silty soils. It can be used on land with a high-water table or sandy soil.
Pile foundation is typically used for two types of construction. This includes either for adding on to an existing building or for supporting a new one.
Generally speaking, pile foundation is preferable for construction in areas that are subject to strong winds, earthquakes and flooding.
One of the most common types of residential foundation is pile foundation. Primarily, pile foundation is used for properties that are on a slope or sloping lot. As a result, the piles are used to create a flat surface for the home to be built on.
A foundation, such as pile foundation, is an important part of any home, including residential homes. The piles are intentionally sunk below the ground level to allow for maximum stability.
As a result, the weight of the house is transferred to the ground rather than the foundation.
The stability of the house is also increased as it builds a strong support base and resists the natural downward pressure of the soil.
In summary, the following are the most common uses for piles in foundation:
- To bear vertical compression load.
- To handle an uplift load.
- To withstand horizontal or angled loads.
Pile Foundation Methods
What piles foundation methods is used?
Driven piles are installed using impact vibration hammers (piling rig) to a specific depth, designed by piling experts.
The different types of pile driving methods are:
- Hydraulic hammer
- Air hammer
- Hydraulic press
Pile Foundation Depth
What is the pile foundation depth?
The depth of a pile foundation is an important factor to take into consideration when building a structure. The technique for building a pile foundation typically involves increasing the thickness and depth of the pile from the ground upward. Additionally, the piles can be drilled to a specific depth as well. The pile needs to reach solid ground to create the foundation of the structure.
Normally, pile foundation depths range from a few meters to roughly 30 meters, although under rare conditions, piles have been driven down to 150 meters. Steel circular piles used in offshore construction can go substantially deeper.
The depth pile foundations can go down to a great depth. A typical pile depth will vary from site to site, depending on many factors such as the type of soil.
Here are the factors to consider when determining Pile Foundation Depth?
- Load size to be transmitted from the structure to the foundation.
- Soil bearing capacity
- The depth of water below the ground surface.
- Soil types and layer depths in the case of layered soil
- The depth of the adjacent foundation.
- Space availability
- Sensitivity to noise and vibration.
Note: Pile Foundation Minimum Depth; If the weight on the foundation is between 2000KN and 3000KN, the minimum depth for a pile foundation is between 6.0m and 20.0m with pile caps.
Pile Foundation Maximum Depth: Concrete pile foundations can be driven to depths of more than 30 meters attributable to the use of pile joints. Typically, piles in pile foundations can be driven down to a depth of 30m; but, in exceptional situations, such as offshore projects, piles can be driven down to a depth of 150m.
Pile Foundation in Black Cotton Soil
The pile foundation is used to carry large loads in black cotton areas from the structure to bedrock rock layers that are much deeper below earth’s surface and when shallow or mat foundations are not practical due to weak or expanding topsoil in the top surface.
The pile foundation also helps prevent the building from being uplifted by lateral loads such as earthquakes and wind forces.
Hard rock strata can range in depth from 4m to 30m below the natural ground surface, depending on local topography and geology.
The pile foundations withstand structural loads by skin friction and end bearing. The use of piling foundations also prevents foundation settlement.
Pile Foundation Design Details
Pile Foundations Advantages and Disadvantages
In the construction of a building, a pile foundation is one of the most common methods to build a strong foundation. It allows for easy excavation and long-term stability.
Pile Foundations Advantages
Advantages of Pile Foundation includes;
- Pile foundation is economical when the soil conditions are suitable, it is a cost-effective way to construct structures in areas with loose soil.
- Pile foundations can be driven into the ground at any depth up to a point where the ground is considered strong enough to carry building loads.
- Piles can be installed by machine and it takes less time than other foundation systems.
- Pile foundation can be used when the ground surface is very weak, such as in swampy areas.
- Pile foundations can be adapted to almost all soil types.
- Piles can be driven -in hard ground and hard rock layer at a low cost; and this helps avoid the use of heavy earth-moving equipment through the area of construction, while providing a surface for buildings to be placed on top of them.
- Piles are used in construction of ductile concrete piles such as electric towers in the case of weak soil conditions, or when it is dangerous to drive heavy equipment through the area of construction.
Pile Foundations Disadvantages
- The ground conditions must be favorable to avoid foundation settlement, uplift and heave.
- Pile foundations are impractical where the water table is close to the surface and where access is required on higher ground for construction equipment and materials.
- The costs may be high if piles have to be driven into hard rock (e.g., rock anchor pile) or in cases where a lot of piling equipment is required for driving piles and compaction of sub-grade soils during pile installation (e.g., vibratory hammer).
Pile Foundation FAQs
1. What is pile foundation?
Pile foundation refers to the construction of a new foundation or addition of an existing building that is supported by one or more vertical piles.
A pile, technically, is not a single unit but rather an assembly of multiple parts. It is categorized as either temporary or permanent.
2. What are the advantages of pile foundation?
Pile foundation is an economical method of supporting a structure because it is simple to install, easy to manufacture and less expensive as compared to other methods.
It can also be easily customized in terms of size and depth depending on the needs or requirements of the structure.
3. How many types or categories are there for pile foundation?
There are four main categories when it comes to pile foundations: mat, raft, spread and stem wall. Each of these categories has a different level of difficulty and costs associated with them.
4. How much does pile foundation cost?
The price of pile foundation depends on the type, grade or grade, and length or depth of the existing piles and the type or size of foundation being used.
5. What is a structural pile foundation?
A structural pile foundation is a foundation that is used to support a structure and it consists of multiple piles that are driven deep into the ground to provide structural support to a building or other structure.
6. What are the advantages of pile foundation compared to other methods?
Pile foundation is able to withstand the load from any structure built on top of it due to its design and construction.
Additionally, this type of foundation is not as expansive as other types and is also less expensive than concrete or rock-based materials such as steel beams.
7. What are the factors that determine pile foundation costs?
There are many factors that determine pile foundation costs. The price will depend on the type of structure and soil. The price also depends on the manufacturer and their labor rates as well.
8. What are the stages of pile foundation construction?
There are four main stages when it comes to piling foundation construction: foundations, driving, installation and post-driving.
The foundations are constructed prior to driving or installing the piles. The piles are then driven into the ground by an excavator and then finally installed or post-driven.
9. What is the minimum depth for a pile foundation?
The minimum depth for a pile foundation is determined by soil type, the weight of the building, as well as other factors such as wind loads and seismic activity in the area.
The resulting load from these factors determines what size pile to use as well as where to place it on the building site.
10. How many types of pile foundations are there?
There are four main types of pile foundations: mat, raft, spread and stem wall. Each type serves a different purpose and has a different cost associated with it.
11. What is a mat foundation?
A mat foundation is a type of pile foundation that is built on top of the ground level by driving or installing the piles into the ground.
It is most commonly used on softer or weaker soil and is easiest to install. The size, type and depth of the piles are determined by the type of soil that they are being driven into.
12. What are some disadvantages of pile foundations?
Some of the disadvantages of pile foundations are they are generally more expensive than other foundations.
Also, the installation process is very hazardous and only a few well trained and experienced personnel should be allowed to work on them.
13. What is a raft foundation?
A raft foundation is also a type of pile foundation that is designed to support a structure that sits above the ground level with a sub-structure that extends below the ground level by means of one or more concrete or steel beams. The size, type and depth of the steel beams are determined by the amount of weight to be supported.
14. What are some disadvantages of raft foundations?
The disadvantage of a raft foundation is that it costs more than other foundations because it requires steel beams to support the structure and steel is more expensive than other locations.
15. What is a spread foundation?
A spread foundation is characterized as a pile foundation where one or more concrete or steel beams are placed in the ground with their ends extending beyond the ground surface. The size, type and depth of the concrete or steel beams are determined by the structure’s weight.
16. What are some disadvantages of spread foundations?
The disadvantages of a spread foundation are that it is expensive, difficult to construct, and should only be used in areas with suitable soil conditions.
17. What are pile foundations used for?
Pile foundations are principally used to transfer the loads from superstructures, through weak, compressible strata or water onto stronger, more compact, less compressible, and stiffer soil or rock at depth, increasing the effective size of a foundation and resisting horizontal loads.
18. What are the factors to consider when deciding whether to use a pile foundation?
The factors to consider when deciding whether to use a pile foundation are soil conditions, load requirements, and structure type.
For example, if the soil is soft or weak, if there are seismic or wind load requirements, or if there is sandy or loose soil, then the piles should be used as a basis for the structure to be built.