UnRing: seeing the toe through the ringing

Every PET user has met this pile: the hammer blow looks fine, but then the whole curve starts to ring like a bell, one even wave after another, all the way down. Somewhere near the top of the pile there is a feature - a change in section, a joint, a hard soil layer - that reflects the wave back to the head. The wave then bounces between the head and that feature again and again. We call it a reflector, and the ringing it leaves behind can be stronger than the echo from the toe.

That is the problem: the toe is still there, but it is buried in the ringing. The analyst has to guess which of many similar dips is the real toe, and often the honest answer is "length unknown". UnRing is a new PET option built for exactly these piles.

The idea is simple. A ring repeats itself: once you have seen one wave, you know what the next one will look like. UnRing finds the rhythm of the ringing, predicts it, and takes it away. Anything that does not follow that rhythm - the toe, or a real defect - is not predictable, so it stays. Here is a 22 m pile from our archive, before and after:

Before, the dip at the toe looks much like a dozen other dips above it. After UnRing, the curve is quiet down to 20 m and the toe at 22.1 m is the obvious feature.

UnRing is an option you turn on for a single pile, when you see a ring. It changes only what is drawn on the screen; the recorded data is never touched, and one click brings the original curve back. We tested it on the 1,000 most strongly ringing piles in our archive of field tests, and on almost half of them the toe became clearly easier to see.

It is not magic, and it is not meant for every pile. When the toe echo itself happens to repeat at the same rhythm as the ring, UnRing can weaken it too, so always compare the curve with UnRing on and off before you decide. As with every PET tool, the length is still the engineer's call - UnRing just gives you a clearer picture to make it.

Arrow pointing to the UNRING function button in the PET software 6.x