Pile Foundations in Civil Engineering: Different Types
When the carrying capacity of the surface soil is insufficient to withstand the loads produced by a structure, deep foundations are typically used. As a result, the loads must be moved to a deeper level, where the soil layer's bearing capability is larger.
Foundations could be categorized under shallow or deep foundations. While shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils, the deep foundations are necessary where the bearing capacity of the surface soils is insufficient to support loads imposed. It is such that they can be transferred to deeper layers with higher bearing capacity. And, pile foundations are used to transfer the loads from superstructures, through weak, compressible strata or water onto stronger, more compact, less compressible & stiffer soil or rock at depth, increasing the effective size of a foundation and resisting horizontal loads.When the carrying capacity of the surface soil is insufficient to withstand the loads produced by a structure, deep foundations are typically used. As a result, the loads must be moved to a deeper level, where the soil layer's bearing capability is larger
In this article, I will talk about pile foundations, their general uses, different types of pile foundations in civil engineering, and when to use them.
What is Pile Foundation?
A pile is a long, strong cylinder of concrete driven into the ground to provide a secure foundation for constructions built on top of it. Pile foundations are primarily used to transfer loads from superstructures to stronger, more compact, less compressible, and stiffer soil or rock at depth, increasing the foundation's effective size and resisting horizontal loads. They are often employed by civil and structural engineering firms for huge structures and when the soil isn't adequate for preventing excessive settlement. Because pile foundations bear such a heavy load, they must be meticulously built. A qualified engineer will examine the soil in which the piles are set to ensure that it is not overburdened beyond its bearing capacity
When is Pile Foundation Used?
The conditions in which a pile foundation system can be beneficial are as follows:
- When there is a lot of water in the ground.
- Heavy and non-uniform loads are applied to the superstructure.
- Other foundations are either too costly or too complicated to put in place.
- Due to its proximity to a riverbed or the coast, there is a risk of scouring.
- When the structure is located near a canal or a deep drainage system.
- Due to unfavorable soil conditions, excavating to the necessary depth is impossible.
- Soil that is close to the surface and has a low carrying capacity (700 pounds per square foot or less)
- Soils with expanding clays near the surface (shrink/swell soils)
- Surface soils that are at risk of being washed away due to erosion or scour
- Due to a significant inflow of seepage, it becomes impossible to keep the foundation trenches dry by pumping or any other means.
Types of Pile Foundation
Based on Function or Use
- Sheet Piles - Sheet piles are structural elements that, when joined, form a continuous wall. They're typically employed to keep dirt in place or keep water out. The wall is held together by interlocking mechanisms generated during the manufacturing process. Sheet piling can be made out of various materials, as detailed further below. Steel is the most popular choice because of its availability, relative strength, and ease of storage, handling, and installation. They are commonly used for the following purposes:
- Retaining wall construction.
- Erosion protection on riverbanks.
- Keep loose soil out of foundation trenches.
- To isolate the foundation from the soils around it.
- To limit the soil's carrying capacity and increase the earth's bearing capacity.
- Load Bearing Piles - The material, installation technique, equipment utilized for installation, and arrangement are used to classify load-bearing piles. They can also be classified according to how they transfer load from the pile to the soil mass: friction, toe bearing, or both. Steel, concrete, lumber, and plastic are the four main forms of weight-bearing piles. This type of pile foundation transfers vertical loads from the structure to the soil. It transfer loads from a layer capable of sustaining the load to the one with weak supporting properties. Load-bearing piles can be further classified as flowing based on the technique of load transmission from the pile to the soil.
- End bearing Piles - The loads pass through the lowest tip of the pile in this sort of pile. The bottom end sits on the surface, formed by the intersection of two weak and strong layers. As a result, the load is safely transferred to the strong layer, bypassing the weak layer. The total capacity of an end-bearing pile is estimated by multiplying the pile's tip area by the soil's bearing capacity at the pile's resting depth. The diameter of the pile is determined using an appropriate safety factor.
- Friction Piles - When the soil is soft, no firm strata are available. To increase surface area and frictional resistance, the piles' surfaces have been roughened. They are based on frictional resistance between their outer surface and the soil they come into touch with. Firm strata do not support these heaps. To put it another way, the pile's entire surface, which is cylindrical, works to transfer forces to the soil.
Based on Materials and Construction Method
- Timber Piles - Under the sea level, timber piles are erected. They last for roughly 30 years on average. They come in a variety of shapes, including rectangular and circular. They can range in size from 12 to 16 inches in diameter. The pile is typically 20 times the width of the top. These are the oldest of all the piles now in operation. Precast displacement piles are often installed using the drive method or, less commonly, the vibratory method.
- Concrete Piles - Precast and Insitu concrete piles are the two types commonly employed. If the precast concrete piles are rectangular, they are cast horizontally in the pile bed. Circular heaps are typically cast vertically. Precast piles are frequently strengthened with steel to minimize breakage during mobility from the casting bed to the foundation location. On the other hand, cast in situ piles are built by driving a metallic shell into the ground and filling it with concrete, then leaving the shell in place while the concrete is poured, or by pulling the shell out while the concrete is poured.
- Steel Piles - Steel piles have the highest allowable operating stresses of any piling material, but they aren't necessarily the strongest in terms of the material's ultimate strength. Steel heaps are generally high-capacity piles that may be employed for various loads. Also, steel tubes can be driven in both closed and open-ended configurations. A high-frequency oscillation hammer or a percussive hammer gives the energy to drive the piles.
Conclusion
Because pile foundations bear such a heavy load, they must be meticulously built with the assistance of a civil and structural engineering firm. A qualified engineer will examine the soil in which the piles are set to ensure that it is not overburdened beyond its bearing capacity.
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