Imaging-Based Parallel Seismic Test for In-Service Bridge Pile Foundations

The conventional parallel seismic test (PST) is a widely used and highly reliable method for determining lengths of in-service bridge pile foundations. However, it relies solely on the manual interpretation of first-arrival in seismic records and often fails to detect, characterize, or geometrically define internal defects within the piles. To overcome these limitations and enable the intuitive identification of internal defects and damage within piles, this study introduces an elastic reverse time migration (ERTM) imaging algorithm based on the spectral element method, achieving high-resolution imaging of existing bridge pile foundations and their defects and damage. To suppress crosstalk between P- and S-waves during the ERTM process, a wavefield decoupling method is employed to separate the elastic wavefield into P- and S-wave components for independent imaging. Two-dimensional numerical testing on a bridge pile model with a necking defect demonstrates that ERTM can effectively image both the pile geometry and its defects, significantly improving the capability of defect detection and characterization. This approach provides more intuitive visualization for assessing the structural integrity of in-service bridge pile foundations.