Advances in Stress-Wave Nondestructive Testing Methods for Evaluation of Deep Foundations-Article

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The paper presents two prototype stress-wave nondestructive testing systems aimed at addressing gaps in quality assurance and control of deep foundations. Existing methods often require access tubes or are limited to testing foundations during construction, leaving in-service foundation defects and conditions beneath drilled-shaft bases difficult to assess.<br /><br />The first system uses an ultrasonic probe lowered into a borehole beside a foundation, without requiring instrumentation installed in the foundation. In laboratory tests, it detected defects in models of a steel pipe pile and a concrete drilled shaft. Reflections revealed corrosion-like steel section loss, a large concrete void, and exposed reinforcement. Estimated changes in pipe thickness were reasonably close to the known model dimensions, demonstrating potential for assessing in-service foundations.<br /><br />The second system was designed to identify anomalous features beneath drilled-shaft excavations, such as weak seams in karst. Laboratory tests detected several seams, but the high-frequency signals had limited penetration and did not fully resolve deeper features. Numerical modelling showed that full waveform inversion could produce more detailed images of complex subsurface anomalies than basic reflection imaging, although results were affected by limited depth of investigation and inversion artefacts.<br /><br />Overall, the experiments provide promising proof of concept for high-resolution imaging of foundation defects and subsurface conditions. However, both systems require further development and scaling for field use, particularly to improve exploration depth, image interpretation, and reliability under complex real-world conditions.

Keywords

stress-wave nondestructive testing

deep foundations

quality assurance

ultrasonic probe

borehole inspection

foundation defects

drilled shaft

subsurface anomalies

full waveform inversion

karst seams