Distributed Fiber Optic Monitoring of Non-Uniform Deep Foundation Strain-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes distributed fiber optic sensing (DFOS) used to monitor strain and temperature in Caltrans post-grouted drilled shafts. In a Sacramento field test, researchers instrumented four test shafts and nine reaction shafts, recording behavior during grouting and top-down load tests.<br /><br />DFOS turns an installed fiber-optic cable into a continuous series of measurement points, providing strain or temperature data along the cable rather than only at discrete sensor locations. Brillouin-based systems can monitor long distances, though spatial and strain resolution vary by analyzer type. Temperature effects on strain readings can be addressed by installing separate strain-sensitive and temperature-sensing cables.<br /><br />Load-test measurements showed that fiber optics can capture non-uniform, complex strain patterns that point sensors may miss. Comparing DFOS with vibrating-wire gauges also demonstrated the risks of automatically discarding a measurement that appears to be an outlier. In one example, removing a suspected outlier would have raised the estimated average axial strain by 30% and obscured bending likely associated with non-concentric casing.<br /><br />The findings indicate that DFOS is a viable method for monitoring deep-foundation performance and is especially useful where behavior varies along an asset. For reliable interpretation, engineers should consider the physical context of measurements, plan the monitoring system and installation carefully, and use at least four measurement lines or gauges where possible to distinguish axial strain from bending.

Keywords

distributed fiber optic sensing

DFOS

Caltrans

drilled shafts

strain monitoring

temperature monitoring

Brillouin sensing

load tests

deep foundations

vibrating-wire gauges