Scour Monitoring Around Piers to Recognize Critical Conditions for Existing Bridges

The functionality of a river crossing must be ensured not only under normal conditions but especially during hazardous events, e.g. floods, when the efficiency of the infrastructure becomes fundamental to ensure the mobility of the rescue teams and the evacuation of the inhabitants. However, this is not currently accomplished, so that hydraulic phenomena account for over 50% of bridge failures. Among the hydraulic causes, the localized erosion at bridge piers that mainly develops during flood events plays a relevant role, also because it cannot be recognized or detected through a simple visual inspection. This study explores the ability of sonar sensors to continuously monitor the scour evolution, and investigates sensor measurements in several locations around piers comparing them with maximum scour depths. Laboratory experiments have been developed in a 1 m-wide flume using nearly uniform sand to simulate riverbed conditions. The scour around an elongated pier on a rectangular foundation tilted respect to the flow direction was simulated. The obtained results show that sonar sensors in clear water conditions can effectively monitor the scour evolution over time, and this is useful to acknowledge a critical condition even if their placement does not correspond to the one where the maximum scour depth develops. In all the examined cases, the continuous monitoring data are consistent with the photogrammetric survey of the scour at fixed time. From the developed experiments, the effectiveness of the sonar sensor to acknowledge maximum scour depths can be deduced.