Under reamed piles have mechanically formed enlarged bases that have been as much as 6 m in diameter.Under reamed piles are the most safe and economical foundation in Black cotton soil. Under reamed piles are bored cast in situ concrete piles having bulb shaped enlargement near base. A Pile having one bulb is called single under reamed pile. In its closed position, the under reamer fits inside the straight section of a pile shaft, and can be expanded at the base of the pile to produce the enlarged base. The cost advantages of under-reamed piles are due to the reduced pile shaft diameter, resulting in less concrete needed to replace the excavated material. Under reamed piles are of two types:

Pre-cast under reamed piles Pre-cast piles require specialized pile driving equipments. And its advantageous over in-situ cast pile because they don't need holes to be bored and the pile is already cast complete with the reinforcing steel in place.

In-situ cast under reamed piles It is used to replace soil removed by drilling rather than occupying the space of displaced soil as in driven piles and thus, it mostly relies on end-bearing capacity of the earth layer at the drilled depth.


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