Pile Integrity Testing

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Effects of Reinforcement on Pile Integrity Testing and Possible Ssolutions

Pile Integrity Testing (PIT) is a nondestructive low strain method used to determine the either the integrity or the length of the pile based on a known or assumed wave speedfor testing pile integrity in concrete piles. This method involves mounting an accelerometer on the pile top and sending a force wave through the pile using a set ofsmall hammers varying from 1 lb to 8 lb. When the hammer impact sendsprovides the stress impact wave through the pile, the accelerometer response is recorded on the PIT. Usually, tThe output is velocity over the time scale.

Typically concrete shafts at construction sites which need pile integrity assessment have steel bar reinforcements in them and these reinforcements stick out 1.5 to 3 m10 ft above the pile top. depending upon other factors. In general PIT records obtained on piles without reinforcements exhibit a smooth record where the velocity has an initial impact pulse. Beyond this the curve tends to shift downward due to soil resistance before it reaches the toe showing a rise in the curve again. The above described is an ideal record rarely realized under field conditions. Small variations in the pile cross sections, bulges and defects tend to change the shape of the output record. While these can be analyzed and conclusions regarding the location of the defect or bulge or excessive soil resistance or lack of soil resistance can be arrived at, distortions caused in the record due to wave traveling through the reinforcement at a different frequency and the lateral vibration caused in the steel make it difficult to analyze records and arrive at conclusions.

When athe hammer is impacted is applied on the pile top, the stress waves generated there is atravel both downward inwave going to thedown the pile, and an upward wave into the steel bars. The upward waves into the steel bars aregets reflected back and then a set of secondary waves...
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