Distributed Fiber Optic Monitoring of Non-Uniform Deep Foundation Strain-Video

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Video Summary

Andrew Jesko of Geocomp presents a Caltrans research project evaluating distributed fiber-optic sensing for monitoring drilled-shaft piles. The project instrumented test and reaction shafts to measure temperature and strain during curing, grouting, and load testing. Fiber-optic cables provide continuous measurements along a pile, complementing conventional point sensors and revealing how strain varies with depth and around the shaft.<br /><br />During load testing, measurements showed substantial variation among four vertical profiles. This helped identify genuine bending behavior that could have been mistaken for an outlier in sparse vibrating-wire data. Removing that reading would have overestimated strain at the relevant depth by 30% and overlooked bending likely caused by an offset between cased and uncased portions of the pile.<br /><br />The study concludes that distributed fiber-optic sensing is a viable tool for deep-foundation monitoring, particularly when pile behavior is nonuniform. It recommends placing strain sensors in at least four quadrants to distinguish bending from axial strain, and emphasizes combining fiber-optic expertise with sound geotechnical interpretation.

Keywords

distributed fiber-optic sensing

drilled-shaft piles

Caltrans research project

load testing

strain monitoring

deep-foundation monitoring