Using instrumented particles for monitoring the likelihood of bridge scour protection destabilization
Authors: Valyrakis Manousos , Xu Yi 
Published: February 2023

The risk of scour of hydraulic infrastructure, such as bridge piers and abutments, may considerably rise during extreme weather events. The removal of coarse bed material and consequent critical failure of the riverbed surface layer's protective layer against scour can result from sufficiently energetic flow structures, which normally scale with their cross-sectional lengthscale [1] (typically a naturally formed armour layer or implemented rip-rap protection, comprising of cobbles and rocks). This study intends to directly monitor the likelihood of entrainment of an instrumented particle [2] that is properly positioned on the riverbed surface near a bridge pier, in order to evaluate the probability of critical failure of the scour protection layer. By directly observing (visually with an underwater camera) as well as monitoring with inertial sensors within the instrumented particle its likelihood of being entrained, this study seeks to evaluate and validate the risk of a critical failure of the scour protection layer close to build hydraulic infrastructure (here, a model bridge pier). As the physical model of a bridge pier is laid downstream, a series of flume experiments (four flow rates) are conducted under carefully controlled flow conditions to evaluate the change in entrainment frequencies of the instrumented particle. The experimentally obtained highly resolved (at 200Hz) time series of the instrumented particle's entrainment, are validated with the camera placed underwater, for the various flow conditions. The instances of instrumented particle entrainment - from which the rate of entrainment is found (matching the probability of bed surface destabilization [3]) - are derived from the analysis of fused raw data from the calibrated embedded sensors (accelerometer, magnetometer, and gyroscope) to identify entrainment events. Acoustic Doppler velocimetry (ADV) under proper configurations [4], is used to collect flow profiles at various distances downstream of the model pier in an initial effort to connect the local and dynamic driving processes for particle entrainment to the phenomenologically significant bulk flow and pier characteristics (such as pier lengthscale, average flow velocity and depth, the median size of armour layer particles). In order to examine the incipient destabilization of riverbed material, typically leading to the disruption of the bed surface protective layer and catastrophic scour, this research effectively demonstrates the employment of purpose designed instrumented particles, showcasing it as a method that is affordable, non-intrusive, long-lasting, and with readily accessible results.&#160;References1. Xu, Y., Valyrakis, M., Gilja, G., Michalis, P., Yagci, O., Przyborowski, L. (2022). Assessing riverbed surface destabilization risk downstream isolated vegetation elements, Water, 14(18):2880. DOI: 10.3390/w14182880.
2. AlObaidi, K., Valyrakis, M. (2021). A sensory instrumented particle for environmental monitoring applications: development and calibration, IEEE Sensors, 21(8), pp.10153-10166, DOI: 10.1109/JSEN.2021.3056041.
3. AlObaidi, K., Valyrakis, M. (2021). Linking the explicit probability of entrainment of instrumented particles to flow hydrodynamics, Earth Surface Processes and Landforms, 46(12), pp. 2448-2465 DOI: 10.1002/esp.5188.
4.&#160;Liu, D., AlObaidi, K., Valyrakis, M. (2022). The assessment of an Acoustic Doppler Velocimetry profiler from a user&#8217;s perspective, Acta Geophysica, 70, pp. 2297-2310. DOI: 10.1007/s11600-022-00896-3.