Swelling and shrinkage due to the property of volumetric changes of expansive soil like black cotton soil results movement of the ground producing cracking of the order of (sometimes) 15 to 20 cm wide and 2.5 to 4 m deep. This property is very dangerous for the structures supposed to be founded on it. Many techniques are discussed previously in various post published in this blog. Some of these are provision for reinforced concrete ties or bands all around the main walls of the building, removing entire black cotton soil where possible or commencing construction during dry seasons.
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:
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:
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| Under-Reamed Pile Foundation for Black Cotton Soil |
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| Design guidelines for Under-Reamed Pile Foundation |
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.
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