Full Waveform Inversion of Cross-Hole Stress Waves for Structural Integrity Testing of Drilled Shafts-Paper

Paper

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The study evaluates full waveform inversion (FWI) as a higher-resolution alternative to travel-time cross-hole tomography (CT) for detecting defects in drilled shafts. CT reconstructs velocity from first-arrival times, while FWI compares complete recorded waveforms with simulated signals, potentially using more information and avoiding the need to pick arrival times.<br /><br />The authors conducted two-dimensional numerical simulations of a 1 m diameter shaft containing two low-velocity anomalies, including a small defect approximately 10% of the shaft’s cross-sectional area. They inverted the same synthetic data using FWI and CT. FWI detected both defects and more accurately represented their locations, sizes, and material properties. Its images were smoother than the true model, reflecting regularization and limited wave coverage, and it overestimated the small defect’s size and velocity. CT also identified low-velocity zones, but their shapes and extents were less accurate, making the smaller defect particularly difficult to characterize.<br /><br />FWI required substantially more computation—about 2.5 hours, compared with under 10 minutes for CT. However, reducing the number of sources and receivers by nearly half produced broadly similar FWI results, while cutting the number of recorded traces by about 70% and halving computation time. This suggests that FWI may tolerate less redundant data, potentially reducing field acquisition effort.<br /><br />The findings indicate that FWI could improve defect imaging in drilled shafts, but the study is based on simplified numerical simulations. Further development and practical validation are needed before routine field use.

Keywords

full waveform inversion

travel-time cross-hole tomography

drilled shafts

defect detection

numerical simulation

low-velocity anomaly

waveform comparison

seismic imaging

computational cost

field validation