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What are the meanings of the mathematical terms in failure criteria pile load test?

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Load tests are conducted to verify the design assumptions and parameters such as pile friction in soils and sock socket capacity. There are various failure criteria in current construction industry to determine ultimate load resistance of piles in pile load test. For instance in 90% criterion of Brinch Hansen, it is based on the laboratory measured stress-strain relations of soils and a point is identified in which soil fails. This essentially aims at looking for the ultimate bearing capacity and hence the ultimate loads. In fact, this is not intended originally for piles.

For some failure criteria, it does not target at finding out the ultimate pile capacity. Instead, it looks for the process for onset of soil yielding at the base of pile toe an allows for controlled displacement. For example, one of these criteria is reproduced as follows:

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Criterion for maximum movement = (PL/AE + d/120 + 4) mm
where P is the load, L is pile length, A is the area of pile and d is pile diameter.

This failure criterion was developed based on small diameter driven piles. The term PL/AE refers to elastic shortening of piles. For end-bearing piles, this term is acceptable for usage. However, for friction piles this may not truly simulate the actual shortenings of piles because frictional forces along the pile also come into play. The term (d/120 + 4) represents the amount of soil movement which triggers the yielding of soil beneath pile toe.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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Comments
  • tekle amare November 3, 2011 at 10:23 am

    nice

  • Debal Chatterjee May 17, 2012 at 12:58 am

    Dear Sir,

    A cast in site bored test pile was under test for a safe load of 70 tonne when the hydraulic system failed (due to leakage from hose pipe) after loading reached 80 tonnes with a settlement of 3mm at that stage. Can the same pile be re-tested again and and if yes how?

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