Foundation quality inspection

PURPOSE OF SONIC TEST

Sonic test method is used to determine the concrete pile integrity based on the characteristics of supersonic wave propagation in materials (concrete).


METHOD OF SONIC TEST

The supersonic wave propagates in materials is followed the principle of optical rules such as reflection, refraction and diffraction. When supersonic wave propagating in concrete meets a zone with changes in material characteristics (density, structures), a part of the wave is reflected at the changes, the other propagates around the perimeter of the defects resulted in longer travel time (t), less velocity (V).  In case the defects are holes filled with air, reflection and dispersion which magnitudes depending on the size of holes. Based on the shape of supersonic wave displayed on the screen, pile concrete quality can be evaluated. The supersonic wave reflects the elasticity characteristics of concrete while the changes in amplitude wave reflect the concrete integrity.

Based on the above principles, the pile concrete quality is evaluated on the velocity and waterfall of each profile between a pair of sonic tubes pre-installed in the piles. During testing, the transmitter in one tube sends a high frequency signal that is received by the receiver in another tube. The special monitor records and storages energy and transmitting time of signals along entire pile shaft when pulling at the same time transmitter and receiver at regular depth intervals. The above signals are appeared on monitor screen. The test is then repeated for each pair of sonic tubes.

Note: When determining the homogeneity of concrete by sonic test method, it should be evaluated in combination with the test results of compressing concrete samples and only consider the concrete parts meeting the required strength.


APPLIED STANDARD

  • TCVN 9396:2012 “Bored pile – Determination of homogeneity of concrete – Sonic pulse method”.
  • ASTM D6760-08 “Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing”.
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