Under reamed piles are used for black cotton soil. therefor it is necessary to understand the construction procedure of under reamed piles foundation.
What is Under reamed piles:
Under reamed piles are special types of piles manufactured by the Central Building Research Institute (C.B.R.I). Such piles are made of R.C.C. This type of pile specially design for expansion soil (Black cotton soil).
The bottom end of the pile has a spherical enlarged portion called an under rim or bulb.
The diameter of the pile is 20 cm to 50 cm and the diameter of the bulb is 2 to 3 times the diameter of the pile.
Under reamed Pile lengths range from 3 m to 8 m.
The spacing between the two piles is 2 m to 4 m.
The safe load on the pile is 20 to 40 tons.
The vertical spacing between two bulbs is 1.25 to 1.50 times the diameter of the bulb. More than one bulb is placed if the load on the pile is high.
IS Code for Under reamed piles:
IS 2911-3 (1980): Code of practice for design and construction of pile foundations, Part 3: Under-reamed
piles – Download Here
Under reamed piles are used in which type of soils?
Under read piles foundation is used for the following soils.
1. Under reamed piles are used in black cotton soil:
This type of soil expands when it comes in contact with water and contraction occurs when water is removed. So that cracks appear in the construction done on such clay. An under reamed pile is used in the base to remove this defect.
2. Under reamed piles are used in low bearing capacity Outdated soil (filled soil)
3.Under reamed piles are used in sandy soil when water table is high.
4. Under reamed piles are used, Where lifting forces appear at the base of foundation.
Types of Under reamed pile:
Single-bulb cast-in-situ pile,
A single bulb attached at the bottom end of a pile is called a single bulb under reamed pile. The pile with two bulbs is called a double bulb under reamed pile. And the pile with more than two bulbs is called a multiple bulb under reamed pile.