A critical evaluation of bridge scour for Michigan specific conditions

The overall goal of this research was to improve the Michigan Department of Transportation's (MDOT's) bridge scour prediction capability. In an effort to achieve this goal, the research team evaluated scour prediction methods utilized by state DOTs, conducted a field data collection project, and proposed an alternative approach for pier scour prediction. Nine locations and twelve unique spans were selected for monitoring. During the investigation, seven episodic measurements resulted in detectable pier scour. Scour depths ranged from 0.7 to 1.5 ft with the maximum return period corresponding to a seven-year flood event. No detectable scour events occurred at the continuous scour monitoring locations. This investigation also included the use of a Jet Erosion Test (JET) to experimentally determine if in-situ soil conditions could be correlated with measured bridge scour. The JET was able to correlate erodibility with geotechnical properties such as dry unit weight, soil type, and shear strength, but was not able to aid in the calibration and/or modification of the scour predication equations. In conclusion, a modified Hydraulic Engineering Circular 18 (HEC-18) pier scour prediction equation was developed for application in Michigan using the National Bridge Scour Database (NBSD). This revised scour prediction procedure could allow MDOT to more accurately predict bridge scour and subsequently more efficiently design new bridge crossings and/or modify existing bridges. Finally, experimental and analytical approaches developed during this investigation provides a foundation for future research in the field of scour prediction.