Foundation, Concrete and Earthquake Engineering

What are the Spacing Requirements of Under Reamed Piles?

Under reamed piles are cast-in-situ piles of concrete which have enlargement like bulb near base of pile. These piles are the safest solution for soils that are susceptible to suffer differential settlement or for buildings those are on filler-up soils or for expansive soils like black cotton soil.

The enlarged bulb not only increases the bearing but also provide anchorage of the foundation to eliminate the harm from expansion of soil. Many researches are carried out in India and all over the world to invent the effective foundation solution for black cotton soil. These researches show that the under-reamed piles are the safest and ideal solution for this type of soil.

Under reaming operation for under reamed pilesIn this post we will discuss the spacing of piles that are ideal to have maximum efficiency from under-reamed piles. In this regard, this has to conclude that spacing of piles depends on:

1.Type of piles

2.Ground nature

3.The way in which loads are supposed to transfer from piles to ground

Normally spacing between under-reamed piles do not kept closer than 2 times the diameter of piles (Du). The spacing is measured form centers of piles. Where different pile diameter is used in construction Du is calculated from the average diameter of adjacent piles. In especial conditions where the spacing have to be closer than the above defined value, the spacing of 1.25X Du can be used with a 10% reduction in load bearing capacity of pile. The maximum limit is provided by economy i.e. if spacing becomes 2.5X Du the resulting capping beam is very heavy.

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