>> Under reamed piles have mechanically formed enlarged bases that have been as much as 6 m in diameter. The form is that of an inverted cone and can only be formed in stable soils. In such conditions they allow very high load bearing capacities.
>> 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:
Precast under reamed piles
In-situ cast under reamed piles
Precast under reamed piles
Precast piles require specialized pile driving equipments. They are 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
This type of pile installation 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.
