Under Reamed Piles are Generally

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Under reamed piles are generally

a. driven piles
b. bored piles
c. precast piles
d. all the above

Find the correct answer from the options given above and also provide a detailed explanation of the correct answer.

Answer: c. Bored Piles

Under reamed piles are generally bored piles.


According to  IS2911:1980 (part 3), Clause.2.20, under-reamed piles are bored cast in situ or bored compaction concrete piles with an enlarged bulb made by either cutting or scooping out the soil or by any other suitable process.

As per IS 2911: Part III (Some other recommendations),

  1. The diameter of under-reamed piles may vary from 2 to 3 times the stem diameter depending upon the feasibility of construction. For Bored cast in situ under-reamed piles, the bulb diameter is normally 2.5 times while for compaction piles it is 2 times.
  2. For piles up to 30 cm in diameter, the spacing of bulbs should not be greater than 1.5 times the diameter of the bulb. For piles of diameter greater than 30cm, spacing can be reduced to 1.25 times the stem diameter.
  3. The top bulb should be at a minimum depth of 2 times the bulb diameter. In expansive soils, it should not be less than 1.75 m below ground level. The minimum clearance below the underside of the pile cap embedded in-ground and the bulb should be a minimum of 1.5 times the bulb diameter.
  4.  Under reamed piles with more than two bulbs are not advisable without ensuring their feasibility in strata needing stabilization of boreholes by drilling mud. The number of bulbs in case of bored compaction piles should not exceed two in such strata.

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