Transient Dynamic Response [TDR] method is a low strain dynamic test which provides a rapid and accurate way of assessing the continuity and integrity of concrete pile foundations.
The test is conducted by striking the pile top axially with an instrumented [force response] hammer to induce a longitudinal wave that travels down the shaft. When the wave reaches the base of the pile or encounters an acoustic anomaly, it is reflected back up to the top. A transducer affixed on the hammer and a geophone sensor on the pile top respectively measure the force of the blow and the velocity of the response signal. These signals are digitized and stored on the test unit.
The collected data is conditioned, analyzed and processed via computer software to generate the graphs shown one the next page. Trained personnel examine and interpret these graphs to deduce the following information about the tested pile:
- Pile length, or depth to anomalies
- Pile head stiffness
- Pile shaft mobility – which is dependent on pile section and concrete properties
- Pile toe level
- Shaft restraints
- Over break
- Cracks
- Reductions in section
- Zones of poor quality concrete
