Under reamed piles are the most 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
In-situ cast under reamed piles
Features:

It is 15 to 20% cheaper than the strip footing.
Less material required.
Digging is normal so the work is carried out for anytime of the year.
No back filling is required.
Shoring is not required.
Dewatering is not required.