Pile foundations are deep foundations. It consists of slender columns or long cylinders made of materials such as concrete or steel, which are used to support the structure and transfer the load at the desired
Pile foundations are deep foundations. It consists of slender columns or long cylinders made of materials
such as concrete or steel, which are used to support the structure and transfer the load at the desired
depth, either by end bearing or skin friction function.
A pile is a structural member that is made of either concrete, timber or steel. By using pile, deeper
foundations can be constructed, but it does cost more than shallow foundations. The pile is a small
diameter column, which is driven or cast into the ground up to a suitable depth. Piles are commonly
used in situations where loads are heavier than usual or if the soil lacks enough bearing capacity. They
help to transfer the load from the structures to the hard strata in soils. The bottom of the pile that is
being driven into the ground is known as the pile tip. The expected elevation at which bearing capacity is
reached while driving pile is called the estimated tip elevation.
The foundation which consists of piles is known as pile foundation. Foundations are generally divided
into shallow foundation and deep foundation. Pile foundation comes under the latter. Regular or open
foundation is a shallow foundation with spread footing. The foundation may not be deeper than 3 to
4m. They are used in cases where the soil strata offer adequate soil bearing capacity (SBC) at that level.
In contrast, when the soil strata is not competent enough to provide adequate SBC, the building loads
will need to be dispersed to deeper strata. In such cases, pile foundations are adopted.
The main function of the pile is to transmit loads to the lower level of the ground by a combination of
friction pile and end bearing pile at the pile point or base. Pile foundations need to be designed very
carefully as they are meant to carry a lot of load. Each pile has a zone of influence on the soil around it,
so the spacing between the piles must also be carefully done. It must be done in such a manner that the
loads are distributed evenly over the entire bulb of soil that carries them. Generally, a few piles are
grouped together, and then topped with a pile cap. A pile cap is a very thick cap of concrete that extends
over a small group of piles. It serves as the base on which a column can be constructed.
A pile foundation may be required in several cases. For example, piles are used to transmit the load to a
stronger soil layer or underlying bedrock when one or more of the upper soil layers are highly
compressible and too weak to support the load transmitted by the superstructure. Another reason may
be the presence of horizontal forces, like high wind forces or earthquake forces which act in a horizontal
direction. The use of pile foundation helps to counter such forces by resisting bending, while
simultaneously supporting the vertical load transmitted by the superstructure. Uplifting forces such as
pressure from subjacent ground, surface water, etc. also necessitate pile foundations. These usually
occur in case of structures such as transmission towers, offshore platforms or basement mats below the
water table. Probability of soil erosion and presence of expansive soil represent some other conditions
in which pile foundations are generally used.
Types of pile foundations:
Piles are classified into different categories based on various criteria. Based on the type of material used,
they can be grouped into timber pile, steel pile, concrete pile and composite pile. In traditional
construction, wooden piles were used. Nowadays, concrete piles are very common. They are precast i.e.
made at ground level and then driven into the ground by hammering. Concrete piles are extensively
used in areas with corrosive soil. Steel H-piles are also very useful. They can take very high loads and
also saves time during construction as the pile casting process is eliminated.
Piles can also be broadly classified into two types based on the construction method. In pre-cast
concrete piles, the piles are cast in the production yard, cured, transported and driven into the ground.
In contrast, cast-in-situ piles are cast at the place or site where they have to function. This is done by
driving a casing into the excavated hole and filling this casing with concrete.
Based on the load transfer mode or function, piles are divided into friction piles and rock socketed piles.
The former is used in areas where the soil is available for deeper depths. When the pile is getting
terminated in rocks, rock socketed piles are used. The bottom end of the pile rests on a layer of
especially strong soil or rock.
Another classification takes into account the installation method. Bored pile, driven pile and vibrated
pile are the categories coming under this section.
The main advantages of using pile foundation are:
End bearing or compressive strength: Piles are used to transfer the load through soil to a
suitable bearing stratum in order to achieve the required compressive strength, in case of soft
Scour Depth: Sometimes, the foundation will have to build through the river bed and within the
scour depth in the case of construction of structures within water or on river or canal beds. In
such cases, pile foundation is more economical.
Vibration Control: In structures where vibrations are significant such as the foundation of
buildings supporting vibrating equipments like turbines and silos, the use of piles is much more
economical and advantageous.
Rapid Construction: Piles are a good option in constructions where the time schedule is quite
tough. They are easy to design and can also be constructed rapidly.