Real-Time Monitoring of Bridge Scour with Magnetic Field Strength Measurement

Scour was responsible for most of the U.S. bridges that collapsed during the past 40 years. The maximum scour depth is the most critical parameter in bridge design and maintenance. Due to scouring and refilling of river-bed deposits, existing technologies face a challenge in measuring the maximum scour depth during a strong flood. In this study, a new methodology is proposed to integrate passive sensors into the process of bridge scour for real time monitoring during a flood event. Towards this end, a permanent magnet can be embedded in a natural rock to function as a passive sensor, which is herein referred to as a smart rock. The smart rock can be designed such that, once deployed around a bridge pier, it continually falls into the bottom of a gradually growing scour hole and thus registers the maximum scour depth with magnetic field strength measurements. Specifically, this paper discusses the societal needs for bridge scour monitoring, demonstrates the concept and the working principle of smart rocks, and summarizes the findings from various calibration and validation tests recently conducted at Missouri University of Science and Technology and at Turner-Fairbank Highway Research Center. It was demonstrated that the magnetic field strength can be strongly correlated with the increase of scour depth over time. Properly designed smart rocks fell into and remained at the bottom of a scour hole, providing critical data in the process of scour development.