What is the maximum length/diameter (L/D) ratio for low strain integrity (PIT) tests?
The answer depends on pile uniformity, soil strength, and actual length and diameter. Under good conditions, L/D may exceed 30, and even reach 60. See also Question 1031
If the pile is drilled its cross section is not guaranteed to be uniform along its length. Assuming the pile has some natural non-uniformity and that the soil has some reasonable strength, at high L/D ratios it may not be possible to assess the full pile length. However, PIT is still useful to evaluate the upper portion of the pile which is often where defects are located. Comparison of many piles may develop a typical "pile signature" and help identify an unusual pile.
Assuming a drilled pile is not yet installed, a good alternative for high L/Ds is Thermal Integrity Profiling, which has been applied to drilled shafts, bored piles, augercast piles, CFA piles, micropiles, and soil nails. For more information visit the TIP page. Thermal Integrity Profiling evaluates concrete quality and uniformity as a function of the complete pile length and has no depth limit. See Question 1101.