According to construction methods there are three types of pile foundations; driven piles, cast-in-situ-piles, and driven and cast-in-situ piles.
What are the differences, and the advantages, of each one?
Driven Pile Foundations
Driven piles made from concrete, steel or wood are prefabricated off-site, before being placed at the construction site, where they are driven into the ground using a pile hammer.
By driving the piles into granular soil, they displace the equal volume of soil, helping to compact the soil around the sides of the piles and resulting in a densification of the soil. The piles compacting the soil adjacent to it is called a compaction pile; by compacting the soil in this way it’s load bearing capacity is increased.
Saturated, silted and cohesive soils have poor drainage capabilities and are therefore not compacted by the driving of fabricated piles. In order to compact the ground, the water must first be drained. Because of this, stresses are developed adjacent to the piles, increasing the pore water pressure and decreasing the bearing capacity of the soil.
Cast-in-situ Pile Foundation
Cast-in-situ concrete piles are constructed by drilling holes in the ground to the required depth. The resulting hole is filled with concrete. Reinforcements are also used in the concrete as per the requirements. These piles are of a small diameter compared to drilled pairs.
Cast-in-situ piles are straight bored piles with one or more bulbs at intervals. Piles with one or more bulbs are called under-reamed piles.
Driven and Cast-in-situ Piles
Taking the advantages from driven piles and cast-in-situ piles, this procedure of installing both piles is as follows:
A steel sheet diameter of pile is driven into the ground with the aid of a mandrel inserted into the shell. After the shell is driven into the ground, the mandrel is removed so concrete can be poured into the shell.
The shell is made from corrugated and reinforced thin sheet metal or pipes. These piles are known as shell type piles. The piles without shells are formed by withdrawing the shell while the concrete is being placed. In both types, the bottom of the shell is closed with a conical tip which can be separated from the shell.
By driving the concrete out of the shell an enlarged bulb may be formed in both the types of piles. In some cases, the shell will be left in place and the tube is concreted.
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