As the superstructure of modern buildings scale new heights, the substructure is faced with the challenge to sustain the heavy loads it is subjected to. This has led to the advent of deep foundations which anchor the building to the earth and ensure a firm and safe structure. The widely tested and adopted form of deep foundation is the pile foundation. Pile foundation comprises one or more piles driven or set into the earth, and held together by a pile cap. The pile cap ensures that the load of the superstructure is evenly distributed to the piles, which in turn transfer or distribute the load to the earth.
Types of Pile Foundation
Based on how the pile is constructed, the foundation can be classified as a driven or drilled foundation.
Driven Pile foundation / Prefabricated Piles Foundation
Driven pile foundation is one where prefabricated piles are brought to the site and driven into the earth to form the foundation. Thus, a driven pile can be made up of any suitable material like timber, concrete, reinforced concrete or steel.
Drilled Pile Foundation / Cast-in-situ piling
In drilled foundation the piles are cast in position. A pile casing may be driven into the ground and then filled with reinforcement and concrete to form a cast-in-situ pile. Alternatively, a hollow stemmed auger may be used to drill the ground which can be pumped with concrete to build the pile.
Both the driven and drilled methods of pile construction have their own pros and cons. Let’s have a look at a few.
Advantages of driven or prefabricated piles foundation
• Prefabricated piles are ready-to-use piles. This saves time at the construction site.
• As the piles are prefabricated, they can be tested for strength and quality. Any flaw can be taken care of beforehand.
• Prefabricated piles can be driven under water making them suitable for most locations.
Disadvantages of driven or prefabricated piling
• Prefabricated piles may be damaged while driving.
• Additional cost and effort of transportation and handling is incurred for using prefabricated piles.
• Often a prefabricated pile has to be altered in length at the site. This requires extra effort and cost.
Advantages of drilled or Cast-in-situ piles foundation
• These piles do not require any additional cost of transportation.
• The length of the required pile is known which can be cast exactly in site.
• Drilled piles can be under reamed to increase their bearing capacity. Under reamed piles have a larger base and hence more load bearing capacity.
Disadvantages of drilled or Cast-in-situ pile construction
• The quality of the pile cannot be determined. Also, the reinforcement used in the pile might be displaced during casting.
• The fresh concrete can be damaged by corrosive elements in the soil.
• The casting of the pile takes considerable time, thus delaying the pace of construction.
• The piles cannot be cast under water.
• The adjoining walls of the pile may cave in while casting resulting in a structurally weak pile.
Bearing and Friction Piles
Piles may be classified as bearing or friction based on the mechanism in which they transfer load. Bearing piles reach the hard stratum of the earth and thus they act as load transmitters. Friction piles are floating piles which are unable to reach a hard surface and the load is endured by the friction between the pile surface and the soil.