A novel vibration-based monitoring technique for bridge pier and abutment scour

Scouring degrades the overall health of a bridge by removing the bed material surrounding the piers and abutments. If undetected, scour may lead to the catastrophic failure of a bridge resulting in hundreds of millions in repair costs. The loss of a bridge due to undetected scour formations can also hinder emergency evacuations since riverbed scouring typically occurs in peak flow periods such as hurricane or flood events. To take requisite precautions against such catastrophic events, a monitoring system that can reliably detect scour formation, without being adversely affected by the environmental conditions, is essential. This article presents a novel scour monitoring technique that exploits the differences between the low-frequency ambient excitations exerted on a thin, flexible plate located in the flow versus the same device located in the sediment. The underlying principle is that a flexible plate excited by the turbulent flow vibrates at significantly higher amplitudes compared to an identical plate surrounded by sediment. To validate this principle, a simplified numerical model is developed to guide the design of the scaled laboratory device; next, a prototype model is built in the laboratory and tested in an indoor flume. The energy content of the sensor in the flow is measured to be one to two orders of magnitude greater than the sensor in sediment. The findings obtained at various flow conditions indicate that this technique can supply reliable information on the water/sediment interface, and thus scour and refill processes. Experimental results also demonstrate that the presence of a scour hole further improves the ability to detect the interface location. Additionally, the results show that maximum slope of the sensor energy content as a function of the sensor depth can be used as a feature to estimate the water/sediment interface.