A critical evaluation of bridge scour for Michigan specific conditions

2007-0436
2006-0413
The overall goal of this research was to improve MDOTs 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 feet 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 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.