Under reamed piles are bored cast-in-situ concrete piles having at least one number of bulbs framed by extending the pile stem. These piles are most appropriate in soils where significant ground developments happen because of occasional varieties, topped off grounds, or in delicate soil layers.
At the point when just a single bulb is given at the lower part of the pile, it is known as a single Under-Reamed Pile foundation. At the point when at least two bulbs are given at the lower part of the pile, it is known as multiple bulbs Under-Reamed Pile foundation.
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Types of Under Reamed Pile Foundation:
Normally, there are two types of under reamed pile foundation:
- Single bulb under ream pile.
- Double or multiple bulbs under the reamed pile.
Single Bulb Under Ream Pile:
In this kind of pile foundation, the bulb is generally present a couple of meters over the bottom of the pile. And the soil below the bulb works as the single unit of the pile, giving the thick base area for the load transfer.
Load carrying capacity for a single bulb under ream pile foundation can be calculated from the formula given in the below figure:
Double or Multiple Bulbs Under Reamed Pile:
As the name suggests, it has two or more two bulbs in the pile stem. The soil trapped between these bulbs works as a part of the pile increasing the thickness of the pile. Hence, the bearing capacity of the pile foundation increases as the surface area of the pile for friction increases.
Load carrying capacity for multiple bulbs under ream pile foundation can be calculated from the formula given in the below figure:
Uses of Under-Reamed Piles:
- It is used to avoid the undesirable effect of seasonal moisture changes in expansive soils such as black cotton soils.
- It is used to reach hard strata.
- It is used to get adequate capacity for downward, upward, lateral loads and moments.
- It is used to take the foundations below the scour level.
- It is used for factory buildings and machine foundations.
- It is used vibration and noise caused during construction of piles, are to be avoided.
Advantages of Under-Reamed Piles
- Under reamed piles reduced the vertical settlement.
- Less concrete needed to replace the excavated material.
- Bulbs in under-reamed piles are very useful to reduce uplift pressure.