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Pile integrity test(low strain impact integrity test)

         

A pile integrity test is a nondestructive test. Used to determine the integrity of casted piles. It shall be conducted after 7 days from casting date. The concept is to compare the actual velocity of sound wave introduced to pile shaft to standard wave velocity. Discrepancies in wave velocity from standard velocity mean pile damage. Integrity tests evaluate pile cross section, discontinuity of pile shaft, pile length, and quality of pile concrete materials. 
In general, integrity test frequently used for concrete piles. An integrity test is a straightforward and rapid test. Method of conducting the test is straightforward and consuming short time. Also, the results of the test provided abruptly. On the other hand, the test providing an approximate evaluation of pile condition and sometimes test results are not accurate.

The pile head shall be cleaned from any contamination such as oil, grease, or loose concrete. Then a sound wave is introduced inside the pile by impacting small hummer into the pile head, and the sound wave reflected from the pile toe.
Figure 1


The time of blow and reflection of a sound wave will be measured by an acceleration transducer. The discontinuities, such as cracks, the cross-section change, and the change in pile material can affect the velocity of the sound signal, and this can be determined by the velocity VS time graph. The table no:1 illustrating different defects with expected graph shape





Disadvantages of integrity test:

A. Small changes in impedance are not detected.
B. The gradual change in pile diameter is not detected.
C. Curved pile shapes cannot be detected.
D. Small soil inclusions are not detected.
E. Local loss of reinforcement cover cannot be detected.
F. The thickness of debris layer at pile toe cannot be detected.





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