Is Relative Energy in CSL a good parameter for flaw detection?

Why should one bother with examining the relative energy?

1. While FAT (First Arrival Time), the main measurement in CSL, only checks the fastest wave path, RE is calculated by summing all wave paths and therefore covers a larger area of the cross-section.

   1. RE can potentially indicate flaws that are outside the cage (figure below). This was verified by finite element model (FEM) simulations

   2. A solid RE line gives additional assurance of the quality of the pile

      
      

2. While FAT picking (especially in the presence of noise) might be tricky and

subjective, RE calculations are straightforward and objective. Hence, no user

defined parameters and tweaks are needed.

Some of the wavepath is blocked due to a soil inclusion, resulting in a reduction of relative energy

That being said, RE has its own challenges. To begin with, it all starts with how you calculate it.

First, note the formula behind RE that has been set by the ASTM D6760 standard

In Piletest, we set the Amax to a fixed high value. Constant in the software.

In comparison, Other manufacturers use the max energy in each profile as Amax.

This makes their RE values start at 0 (when A = Amax) for each profile, and therefore their RE values are equal to the RE reduction.

In Piletest, RE values of 0 are never achievable, and the RE reduction is made by subtracting RE from the median(RE) of each profile.

RE reduction is important as it is part of categorizing an anomaly according to the DFI whitepaper (2020), as shown in the diagram below daigram

There are advantages to both approaches for calculating the RE; the difference is a fixed offset

Both approaches are acceptable by ASTM D6760.

Some users claim that other manufacturer mistakenly use 10*log(...) rather than 20*log(), which halves their RE reduction values and hides defects. At Piletest, we verified this ages ago by exporting the PDI CHAMP energy values to a spreadsheet and performing the calculations ourselves. (We have also noted PDI about this issue in their software)

Piletest has taken a further step by including both RE value and FAT values, along with their severity, on top of the CHUM waterflaw diagram, as shown below. This gives the user an immediate understanding of the flaw's severity, and the RE and FAT values are shown at each depth. See the attached screenshot with the arrow pointing to the serenity bar.

You may also want to read more about flaw detection and categorization here https://www.piletest-office.com/papers/EnergyinCross-HoleUltrasonicCSL.pdf