Interaction of pier, contraction, and abutment scour in clear water scour conditions

Important considerations for bridge design are safety and economy. Predicting the extent and depth of scour is critical to bridge foundation design to ensure structural stability. However, bridges on waterways are vulnerable to damage due to extreme hydrologic events that cause severe floods. In the USA, more than 60% of bridge damages are due to hydraulic parameters that cause scour of the riverbed. Current design practice recommends calculating the sum of all the interacting components of scour to predict the total maximum scour depth. However, the interaction and simultaneous development of scour components results in considerably less scour than predicted. The main objective of this dissertation is to investigate the interactive scour development for all the components of bridge scour (abutment, lateral contraction, vertical contraction, and pier scour) under clear-water scour conditions for erodible, spill-through abutments and rectangular piers. A physical model-based study, which covered all individual and interactive scour conditions, was conducted. The formulated multi-part methodology for total scour prediction to account for scour interactions captures the results within 10% of measured results. The application of the suggested model to field examples validated the findings. The results will not only improve economical bridge design but will also result in reliable hydraulic variables input to the model methodology. In summary, this study provides a comprehensive picture of the interactive bridge scour process and suggests a practical methodology to predict more economical design of safe bridges.