Effects of Cohesive Material Properties on Local Scour Around Piers

Local pier scour has been the topic of numerous research studies on noncohesive alluvial materials. However, because of the complexities involved in cohesive-material scour, very little effort has been devoted to the study of scour around bridge piers situated in cohesive materials. The parameters that affect the scour mechanism at bridge piers located in saturated and unsaturated clayey soils are identified, and prediction equations for quantification of the effects of some of the cohesive properties on the resulting local scour are developed. The scour depth predictors developed from the analysis of the experimental data express pier scour in terms of the approach flow conditions, initial water content, compaction, and soil shear strength of the cohesive bed materials. These predictors are related to scour in noncohesive alluvial material to derive factors that express clay scour as a percentage of sand scour. At bridge locations where exact soil properties are unknown, these estimators may be used to provide bounds to scour estimations.