Bridge Scour Monitoring
A National Science Foundation and later U.S. Army Corp of Engineers funded project.
Project title: Scour Monitoring and Failure Prediction for Safe and Resilient Infrastructures
Source of support: National Science Foundation and U.S. Army Corp of Engineers
Scour is a leading cause of bridge collapse worldwide. Scour monitoring can prevent scour-induced damage and failure of overwater bridges and infrastructure systems. A novel piezoelectric scour sensing technique with the potential of continuous and robust monitoring during flood events is proposed. A small-scale piezoelectric rod functioning based on the concept of a vibrating cantilever beam is designed, fabricated, and calibrated (Fig. 1). A piezoelectric thin film was embedded in a rod, and the piezoelectric scour rod was buried beneath the bed. When scour erodes soil and sediments near the vicinity of the buried rod, flow would induce vibrations of the buried rod and piezoelectric sensing element. By monitoring the generated voltages and by extracting the characteristic vibration properties of the buried rod, the exposed length (or equivalently scour depth) was be determined (Fig. 2). Laboratory-scale validation tests were performed in which a network of these buried rods was installed. A relationship between the excitation-fluid velocity and the vibration frequency was discovered and accounted for through calibration testing and fluid-structure interaction modeling. Large-scale sensors, up to six feet, were successfully tested in collaboration with the U.S, Army Corps of Engineers and the U.S. Army Engineer Research and Development Center. Current work focuses on improved passive piezoelectric monitoring by utilizing piezoelectric rods optimized for multi-modal sensing. A collaboration with wireless electronics company Elintrix aims to simultaneously develop compatible wireless data acquisition hardware along with a custom user-interface. See Video 1 for a laboratory demonstration of the sensing and data acquisition system.
The second sensing system utilizes commercially available miniature dissolved oxygen (DO) probes (Fig. 3). DO probes operate as scour sensors due to a pronounced difference between the oxygen levels in the riverbed and flowing water. Both sensing techniques were examined when deployed as arrays around a small-scale bridge pier in flume tests. It was demonstrated that both sensors can detect scour as it occurs and continue to function as soil is redeposited in the scour hole. Ongoing research is aimed at creating a practical cost-value framework for scour sensor selection and interpretation.
Read more about this topic in an article published in The Economist.
Prof. Michael Todd, UC San Diego
Prof. Chin-Hsiung Loh, UC San Diego
Elintrix (Escondido, CA)
M. Funderburk, S-K. Huang, C-H. Loh, and K. J. Loh, 2019, “Densely Distributed and Real-time Scour Hole Monitoring using Piezoelectric Rod Sensors,” Advances in Structural Engineering (1369-4332), Sage. DOI: 10.1177/1369433219831124
F. Azhari and K. J. Loh, 2016, "Laboratory Validation of Buried Piezoelectric Scour Sensing Rods," Journal of Structural Control and Health Monitoring (1545-2263), Wiley. DOI: 10.1002/stc.1969
F. Azhari and K. J. Loh, 2016, "Dissolved Oxygen Sensors for Scour Monitoring," IEEE Sensors (1530-437X), IEEE, 16(23): 8357-8358. DOI: 10.1109/JSEN.2016.2613123
F. Azhari, P. Scheel, and K. J. Loh, 2015, “Monitoring Bridge Scour using Dissolved Oxygen Probes,” Structural Monitoring and Maintenance (2288-6605), Techno-Press, 2(2): 145-164. DOI: http://dx.doi.org/10.12989/smm.2015.2.2.145
K. J. Loh, C. Tom, J. Benassini, and F. Bombardelli, 2014, “A Distributed Piezo-polymer Scour Net for Bridge Scour Hole Topography Monitoring,” Structural Monitoring and Maintenance (2288-6605), Techno-Press, 1(2): 183-195. DOI: 10.12989/smm.2014.1.2.183
Fig. 1: Buried cantilevered piezoelectric scour sensors are excited by ambient flowing water, and their dynamic properties vary depending on their exposed lengths (scour depth).
Fig. 3: Dissolved oxygen sensors are buried along a bridge pier, and drastic changes in DO levels indicate their exposure to ambient water due to scour.
Fig. 2: Buried piezoelectric scour sensors only required a single voltage measurement, and the raw data could be processed to obtain scour depths that coincided well with manual measurements obtained during a flume test.
Video 1: Piezoelectric scour rods are interrogated and the data processed in real-time time to determine their exposed lengths (or scour depth).