It is found that under-reamed piles provide an ideal solution to foundation in black cotton soil or other similar types of expansive soils. The design guidelines of under-reamed pile are briefly discussed below:
The diameter of the pile stem (D) varies from 20 to 50 cm. The diameter of the under-ream bulbs (Du) is normally 2.5 times the diameter of the pile stem. It may however, vary form 2 to 3 times (D) under special circumstances.
In case of double or multi-under-reamed piles, the centre to centre vertical spacing between two bulbs may vary from 1 ¼ to 1 ½ times the under-reamed diameter (Du). The length of under-reamed piles varies from 3 to 8 meter and their centre to centre spacing should normally be not less than 2 times the under-reamed diameter.