| Bridge scour, the leading cause of bridge failures in United States, is due to the erosion of soil by flowing water. Scour in cohesive soils is much different from scour in non-cohesive soils on scour rate, scour hole distribution, and final scour depth. Applying the solutions for non-cohesive soils to cohesive soils will result in significant errors.; Pier scour and contraction scour are two important components. In the present study, a systematic investigation was carried out by conducting a series of flume tests on complex pier scour and contraction scour in porcelain clay.; For complex pier scour, the individual and combined effects caused by shallow water, pier spacing, pier shape and flow attack angle are examined. Correction factors with respect to the simple pier scour case are proposed. In addition, a thorough shear stress approach is developed for complex pier scour, where the influence of soil properties on pier scour is fully represented by the involvement of the critical shear stress of the eroded soil.; For complex contraction scour, a methodology is developed to predict the contraction scour depth along the channel centerline, including the maximum contraction scour and the uniform contraction scour. The soil critical shear stress is also involved in the prediction process as well as correction factors for the contraction length effect and the transition angle effect with respect to a long contraction channel scour case.; Finally, the integration method is developed to calculate the total bridge pier scour with the presence of bridge abutments, in which bridge contraction scour, abutment scour and pier scour are integrated together based on the concept of the critical shear stress of soil and the relationship between bridge abutment scour and contraction scour that is observed in flume tests.; The results obtained in this study indicate that soil properties really affect the final scour depth through the critical shear stress. However, applications of the currently developed methodology are limited to laboratory conditions. Site verifications are necessary in the future study. |
