Can the Pile Integrity Tester (PIT) be used to evaluate the length and defects of piles supporting existing structures?
Yes, under favorable conditions it is possible to test piles under existing structures with the PIT. In order for the test to succeed, the pile itself must have a relatively solid concrete structure to channel the impact (this can be a solid section concrete pile, or a concrete filled steel pipe).
- If the pile is made out of concrete and the structure is very light relative to the pile or shaft (for example a cell tower where the tower legs are significantly smaller than the shaft), then the structure is almost inconsequential provided there is access to the concrete at the top of the pile or shaft. The PIT test may be performed as usual.
- If the structure is relatively massive, then the shorter the vertical dimension of the cap, the better it is for the test. One accelerometer placed concentrically above the pile may yield good results. Most likely, however, a Two Velocity Test will provide better results. The Two Velocity Test involves placing two different accelerometers along the shaft with ideally about 0.90 m (3 ft) vertical distance between them, and applying hammer blows about 0.30 m (1 ft) above the top accelerometer. This method relies on the phase shift between the two signals to determine whether the details in the signal are travelling up the shaft (from reflections of defects or pile bottom) or down from top after reflection from the pile cap. Because of the recommended vertical distance between accelerometers, this method requires that a sufficient portion of the shaft be accessible. It also requires the use of a Pile Integrity Tester with 2 channels of data acquisition (PIT-FV) and the software PIT-W Professional.
- Whether the Two Velocity Method is used or not, it is helpful to use the PIT-S software to model the pile and see what signals might be expected (with accelerometer and impact locations below the pile top). A demo version of the PIT-S is available as a free download
- H-piles, steel sheet pile walls, or open end steel pipes are not well suited to PIT tests. For these steel pipes testing with the LITE might be an alternative. LITE testing consists of lowering a probe into a borehole parallel and in close proximity to the pile to be tested. The borehole should be lined with a PVC tube to allow access for the LITE probe. The probe detects the presence of metal. Visit the LITE page for more information