Should you trust the constructor for setting the wavespeed in PIT?

This is a very fundamental decision, as the wave speed determines the estimated pile length. Note that the ASTM D5882 for low-strain sonic pile integrity testing (PIT) does not suggest that it can measure pile length. The measurement of the pile length using PIT is just an outcome of determining the integrity of the pile bottom on the PIT reflectogram. So, back to our debate on how to set the wave speed, and whether the contractor's word on the pile length should be used as a reference to set the wave speed.

Wireless PIT = PET from Piletest, for ease of use and high performance

With the PET (Pile Echo Tester) Piletest offers a wave speed calculator. Still, some consideration should be taken when using it.

1. The wave speed suggested by PET's calculator is a first guesstimate. There is a good amount of scatter in its wave speed formula.

2. It is correct to assume that all piles made on the same day, with the same mix, should have the same wave speed.

   1. Assigning each pile in that group a different wave speed to match the desired length is bad practice, and we condemn it whenever we catch it.

   2. Nevertheless, if you have reliable data (for example, a reliable independent inspector, not the contractor. Never trust the contractor!)

   3. Regarding the as-made length, you can use that info in order to modify the wave speed in the whole project (or group of piles) to match that length.

3. Pile integrity testers like PET are much more than length detectors. They are integrity estimators, and the pile's integrity is determined by more than just the as-made length. 

4. Lab tests, such as UPV (Ultrasonic Pulse Velocity) will not show you the real wave speed in a confined concrete cylinder

   1. Ultrasonic (3D) waves have a different speed compared to sonic (1D) waves. Ultrasound is ~10% higher 

   2. A confined concrete beam has a lower wave speed compared to one in air. One needs to include the soil grab in your calculations. Not trivial.
      

THe conclusion 1 - You should rely on multiple inputs to set a wave speed (velocity), and make sure the value does not contradict the expected concrete maturity and planned pile length on all piles. 2 - Good conduct requires setting the wave speed fixed for all piles in a pile group that are equal in age and concrete source or type.