Applying a Passive Vibration Detection Technique to Assess Bridge Pier Scour

Traditional underwater measurements typically require equipment installation in the soil surrounding the bridge pier, which is high-cost and susceptible to flood-induced damage. To overcome these challenges, this research proposed using the passive vibration signal to identify bridge scour. This study conducted flume experiments and implemented in situ monitoring at the Baibufan Bridge in Taiwan to validate the applicability of this approach. The results indicated that the bridge piers’ measured predominant natural frequencies (PNFs) strongly correlate with the time-dependent pier scours. Frequencies along the cross section and flow direction revealed strong relevance with scouring but a low correlation with the gravity direction. The result also revealed that the PNFs must reach a specific magnitude before scouring occurs. It does provide a warning for bridge scour. This study referred to some empirical formula to propose a revised formula incorporating PNFs. The revised formula revealed that the average validation errors decreased from 51.74% to 20.84%. This study proposed a low-cost approach that can be deployed on a large scale. It provided a more economical and complete solution for pier scour.