Friction piles are one of the oldest and most reliable types of deep foundations used in civil engineering construction. Over the years, friction piles have been used to provide a secure foundation for structures in areas of primary soil and shallow rock.
This article will provide an overview of friction piles, discuss their advantages and limitations, and explain best practices for engineers considering using them in their next project.
Friction pile gets its name from the method used to transfer load from the structure to the soil. Unlike end-bearing piles, which transfer the load to the soil through the end of the pile, friction piles rely on the entire length of the pile to resist the load.
To do this, the pile must be installed in such a way that the soil surrounding the pile is unable to move. This is achieved by either installing the pile to a depth where the soil is not able to move or by using temporary or permanent anchors to keep the soil in place.
What are the Friction Piles
Any type of pile foundation can be considered a friction pile in which both the end bearing and friction are taken into account. However, there are piles that only depend on friction.
A friction pile is constructed when there is no rock close to the ground or when the applied load cannot be bearded by the shallow foundation and can be bearded by friction piles.
Mostly, the friction piles are precast concrete piles when they are driven into shallower depths up to about 20m. Increase the depth to the hard soil strata, cast-in-situ piles are constructed as the friction pile. In some locations, the depth of the borehole will be very high. In such cases, we cannot rest the pile on the rock. The only option would become the consideration of the friction of the pile.
How to Calculate File Friction
There are many methods to calculate the friction of the pile. This friction is also known as skin friction. Pile skin friction depends on several factors.
There are two components of skin friction.
- Positive Skin Friction
- Negative Skin Friction
The positive skin friction is the one that resists the applied load on the pile. It transfers the superstructure load to the ground. Negative skin friction is a burden to us. It increases the loads on the pile reducing the geotechnical capacity of friction piles.
Negative skin friction occurs when there is compressible soil such as clay, peat, other organic soils, etc. When the soil moves downwards, the soil tries to drag the pile. As a result of that, there will be a downward force in the pile.
Both positive and negative skin friction shall be considered when designing a friction pile. It has been noted that sometimes there are errors and omissions in consideration of the negative skin friction during the pile design. Therefore, the correct assessment shall be made during the pile design.
The advantages of pile friction are that they are relatively easy to install and do not require as much equipment as other types of deep foundations. Friction piles are also able to resist both compressive and tensile loads, making them suitable for a variety of applications.
The main disadvantage of friction piles is that they are less reliable in areas of high groundwater or soft soils. In these conditions, it is possible for the pile to “float” out of the ground, or for the soil to simply erode around the pile.
When considering whether or not to use a friction pile, engineers should assess the soil conditions at the project site and perform a thorough geotechnical analysis. If the soil is determined to be unsuitable for friction piles, another type of deep foundation should be used.
If friction piles are determined to be the best option, careful attention should be paid to the installation process to ensure that the piles are properly embedded in the soil.