A Review on Bridge Scour Analysis in Cohesive Soils and Scour-Susceptible Rocks

Bridge scour analysis, especially scour depth calculation practices implemented mostly by hydraulics and geotechnical engineers, was traditionally built upon flume tests with cohesionless materials, e.g., sands. As a result, the analysis of bridge scour in cohesive materials, i.e., cohesive soils and scour-susceptible rocks, was less understood and thus has been gaining increasing attention. This paper presents a state-of-the-practice survey on the analysis of bridge scour in cohesive materials represented by cohesive soils and scour-susceptible rocks. This includes a literature review covering the concepts and understanding of scour susceptibility, material sampling, erodibility tests, bridge scour calculation methods for cohesive soils and rocks, and a summary of the information gathered in communications with engineers from state Departments of Transportation (DOTs) in the U.S. Through this review, it was found that scour analysis in cohesive soils and scour-susceptible rocks continues to require further research and engineering development despite substantial recent progress. Undisturbed sampling and appropriate erodibility characterization remain critical for reliable scour prediction. Existing research and engineering practice continue to focus primarily on pier scour, while comparatively limited information is available for contraction and abutment scour in cohesive soils and rock formations. The survey of state DOT practices further indicates considerable variability in the implementation of scour evaluation procedures for cohesive and rock materials, including the use of SRICOS-EFA, the Erodibility Index Method, NCHRP 717, agency-developed procedures, and geotechnical consultation workflows.