Comparison of Borehole Ultrasound and Borehole Radar in Evaluating the Length of Two Unknown Bridge Foundations-Article

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The study evaluated a newly developed borehole ultrasound system for estimating the length of unknown bridge foundations and compared it with commercial borehole radar. Both methods were tested at two Philadelphia bridge sites. The ultrasound system transmitted 100 kHz P-waves from a water-filled, PVC-cased borehole and inferred foundation locations from reflected signals. Laboratory tests showed that, under ideal conditions, reflections could be detected from up to about 0.9 m away, with centimetre-scale resolution.<br /><br />Field results were less reliable. Ultrasound produced potentially useful reflections at one site, including in a clay-rich interval where radar signals were weak, but it could not determine foundation depth at the other site and substantially underestimated depth at the first. Limited wave-propagation distance and sensitivity to probe orientation were identified as key challenges. Borehole radar gave more consistent reflection patterns and more plausible foundation-length estimates at both sites, although clay-rich soils reduced its effectiveness at one site. Estimates from both methods remained crude because the boreholes did not extend far enough below the anticipated foundation bottoms.<br /><br />The authors conclude that borehole radar was more successful in this study, while ultrasound shows research potential—particularly where clay limits radar performance. They recommend improving ultrasound probe orientation, using omnidirectional transducers, and increasing source power. In its current developmental state, the ultrasound system is recommended for research rather than routine foundation assessment.

Keywords

borehole ultrasound

bridge foundations

foundation depth estimation

borehole radar

ultrasonic reflections

P-waves

Philadelphia bridge sites

clay-rich soils

probe orientation

foundation assessment