Field Application of Magnet-Based Smart Rock for Bridge Scour Monitoring

In this study, a smart rock, which is a magnet embedded in a concrete ball and whose direction is always pointing downwards, is proposed to monitor bridge scour depth. Based on the theory of magnetic field, the distribution of the magnet-induced magnetic field (MMF) induced by the smart rock was derived. An algorithm was developed to localize the position of the smart rock. Field tests were conducted at a bridge pier at three different times. Both the intensities of the ambient magnetic field (AMF) and the total magnetic field (TMF) were measured with a magnetometer. Results showed that the presence of steel reinforcement or steel girders in the bridge changed the distribution of the geomagnetic field. The algorithm successfully localized the position of the smart rock with an error ranging from 0.26 to 0.33m, which satisfied the requirement for engineering applications. The effective monitoring range depends on the variation of the AMF, and the maximum monitoring depth ranged from 11.5 to 8.5m as the standard deviation of the AMF increased from 32.3 to 80.75 nT. (c) 2019 American Society of Civil Engineers.