Bridge Scour in Bed Materials other Than Cohesionless Sediments. Part 2

摘要

The soil at many bridge sites in the state of Florida is composed of materialsother than cohesionless sediments (i.e. other than sand, loose shell, etc.). This includes cohesive materials (such as muds and clays), combinations of cohesive and cohesionless sediments, and harder materials such as limestone and coquina. The erosion characteristics of these materials are quite different from those of cohesionless sediments and yet (due to our lack of understanding of their erosion characteristics) they are treated as cohesionless sediments in current design scour prediction equations in HEC-18 (1993). Since the 'erodibility' of these sediments can vary widely, the present approach could be overly conservative in some cases while for other cases scour depths could be under predicted. There is a clear need to improve our ability to predict design local and contraction scour depths in these types of materials. The long-term objective of the work in this study is to provide a means of predicting aggradation and degradation, contraction, and local (structure-induced) sediment scour at bridge sites for the range of bed materials encountered in Florida.