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

This is a very fundamental decision, as the wave speed affects the measured pile length. Note that the method does not directly measure the pile length. The method measures time, which is converted to length by multiplying it by the assumed wave speed (and dividing by 2 because the wave travels down and up). Length=waveSpeed·time/2. The wave speed is not measured. It is assumed. 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.

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

With the PET (Pile Echo Tester) software, Piletest provides a wave-speed calculator based on this paper. An online version is available here.

PET Wavespeed 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 fair 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!) 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 travel at a different speed than 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 input sources to set the wave speed and ensure the value matches the expected based on concrete grade, maturity, and the planned pile lengths for all piles.

2. Good conduct requires setting a fixed wave speed for all piles in a pile group that were made on the same day(s) and with the same concrete.