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Why is the wave speed so slow?

One of our customers recently contacted us, saying his CHUM CSL report shows an unreasonable slow wave speed of 2600 m/s for several of the tested pile profiles. (Below left)

For the analysis, we have plotted the average FAT of each profile vs. the measured distance (above right). As you can see, the slope (which is the true wave speed in the concrete) is 4184m/s, which is very reasonable.

The intercept (fixed offset of the slope on the X-axis) is 0.39m = 100uSec, which is very high.

The high intercept can be attributed to

1. Measuring the tube distances edge to edge instead of center-to-center 

2. The tube diameter is set incorrectly in the software. (It was set to 16cm! Is that correct?)

3. Wrong pile diameter setting (Note that the pile diameter is set to 250m instead of 2.5m?)

Note that when the tube diameter is that large, the wave needs to travel a long distance in water, which is much slower than concrete. The Piletest CHUM has the option to choose an Advanced setting, which compensates for the tube water delay effect on the average wave speed measured in such cases.

4. Consistently wrong FAT picking (Not in this case, the FAT pickings are accurate)

5. Hardware issue

CHUM also has several test methods to run sanity tests on its hardware, as can be seen on the Piletest YouTube channel here

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