Under-Reamed Piles Foundation is an answer in area where black cotton soil could cause structural instability. Many times, during, soils undergo volumetric changes due to moisture variation underneath the ground surface. This expansion and shrinkage can cause distress which is very dangerous and critical as far as bearing of the foundation is concerned. The fact is that Under Reamed Piles are considered as most safe and economical foundation for such black cotton soils or expansive soils.

Under-Reamed Piles are widely used for different types of soils such as sandy soils, clayey soils and also expansive soils. Under-Reamed Piles are required to be taken down to a certain depth because of the following considerations:

• To avoid the undesirable effect of seasonal moisture changes in expansive soils such as black cotton soils.
• To reach hard strata.
• To obtain adequate capacity for downward, upward, lateral loads and moments.
• To take the foundations below the scour level.
• They have also been found useful for factory buildings and machine foundations.
• Under-Reamed Piles are also used under situations, where the vibration and noise caused during construction of piles, are to be avoided.

The Under Reamed Piles have also been extensively used by Sthapati Designers & Consultants Pvt. Ltd., for supporting the floors of large halls, airports etc., at ground / plinth level where there is huge earth filling. If the earth filling is not done in a professional way i.e. in the layer of 20 cm thick with compaction at optimum moisture content, it is likely to settle. Hence to take care of the same, the grade slab was provided on series of Under Reamed Pile spaced at 3 m center to center. Here the grade slab is designed as a flat slab supported on Under Reamed Piles where the pile cap acts as the pedestal of the columns as in flat slab and here no beams are provided for saving the cost. This has also worked and is performing very well since years. This has been done at terminal buildings for Surat and Amritsar International Airports along with many other public buildings.