The effects of ice-water discharge ratio and flow Froude number on local scour around tandem double piers and ice jam thickness in an S-shaped channel

Abstract

In cold regions, bridge piers in rivers can alter flow characteristics and influence the formation and evolution of ice jams, complicating the local scour around the piers and the distribution of ice jam thickness. This study, based on experiments conducted in an S-shaped flume, examines how the flow Froude number and the ice-water discharge ratio affect the local scour depth around tandem double piers and the ice jam thickness. The results reveal that, while a positive correlation exists between the flow Froude number and the scour depth under both open flow and ice-covered flow conditions, the relationship between the scour depth and the flow Froude number under ice-jammed flow conditions is considerably more complex. Due to the influence of the ice jam on scour depth, there exists a critical Froude number at which the relationship between the flow Froude number and scour depth changes. The results indicate that when the flow Froude number is below the critical value, the ice jam thickness decreases slightly, while the scour depth shows a positive correlation with the flow Froude number. When the flow Froude number reaches the critical Froude number, the scour depth peaks. When the flow Froude number exceeds the critical value, the ice jam thickness decreases significantly, and the scour depth becomes negatively correlated with the flow Froude number. Additionally, when the flow Froude number remains constant, an increase in the ice-water discharge ratio leads to a rise in ice jam thickness, which in turn causes the scour depth to increase.