The Significance of the Second Reflection in Pile Integrity Testing (PIT)
- Gadi Lahat
- Feb 15
- 2 min read
The presence of a clear second reflection in a Pile Integrity Test (PIT) signal is a valuable, though not always guaranteed, asset for accurate pile assessment.
Key Benefits and Interpretation:
Verification of Pile End: The primary benefit of a second reflection is that it acts as a strong corroboration for the initial end-of-pile reflection. It provides an additional data point to confirm the depth of the pile base.
Interpretation Aid: As noted by experts, observing the second reflection significantly enhances the signal interpretation's confidence and accuracy. Its presence can be viewed as "a precious present" that simplifies the analysis.
Conditions for Appearance:
The second reflection is only expected to appear under specific, favorable conditions:
Short Piles
Favorable Length-to-Diameter (L/D) Ratio
Soft Soil Conditions (such as soft clay, as mentioned in the case study)
To get an idea about the testability of a pile, use this online calculator
To get an idea about the possibility of getting a second reflection, enter the calculator the pile's length X 2 (Since the wave has to go up and down twice, to get a second reflection)
Use case:
In the PET trace below(shared by a piletest customer):
Individual impact traces are in gray
The average of all impact traces is in blue.
The red triangle on top is the planned length
The red square on the right is the point in the trace that gets the full amplification
The repetition marks [1] and [2] are placed at equal spacing
The pile is planned to be 8m long and 0.4m in diameter with a favorable L/D of 20 installed in soft soil (SPT N=12).
The reflectogram showed a second reflection, confirming a length of 9m, as shown below using the PET Repetition Marks tool.
The customer noted that the second reflection was not visible on all piles. In such instances where these favorable conditions are not met, the absence of a second reflection is not necessarily indicative of a pile anomaly, but rather a result of the soil conditions and pile geometry.
Note that the individual impact traces are repetitive up to about 10 meters, after which they gradually diverge. This indicates that the signal-to-noise ratio of traces at greater depths is deteriorating. As this divergence increases, the traces no longer carry meaningful data.
In other piles in this project, and in most other projects, this divergence occurs at a shallow depth, and no second reflection can be reliably identified.
How it is done with PET
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