Based on two case studies, the impact of ice cover on local scour around bridge piers is presented in this chapter. Bed material with different grain sizes is used and ice covers with different roughness is used to study the scour characteristics. The impact of nonuniformity of sediment is also investigated. Results show that with the increase in densimetric Froude number, there is a corresponding increase in the dimensionless scour depth. For nonuniform sediment, due to the formation of an armor layer, less maximum scour depth was noted around bridge foundation structures compared to uniformly distributed sediment. The increase in ice cover roughness results in a larger scour depth and geometry. The results indicate that it is imperative to pay attention to the impact of ice cover on the scour around hydraulic structures.
Part of the book: Effects of Sediment Transport on Hydraulic Structures
A precise prediction of maximum scour depth (MSD) around piers under ice-covered conditions is crucial for the safe design of the bridge foundation. Due to the lack of information for local scour under ice-covered flow condition, it is extremely hard to give proper estimation of MSD. In the current study, a set of flume experiments were completed to investigate local scour around four pairs of circular bridge piers with nonuniform bed materials under open channel, smooth and rough ice cover conditions. Three different bed materials with median particle size of 0.47, 0.50, and 0.58 mm were used to simulate natural river conditions. Regardless of pier size, the maximum scour depths were observed in front of the piers under all flow conditions. Additionally, a smaller pier size and a larger space between piers yield a smaller scour depth. Results showed that the maximum scour depth decreases with increase in the grain size of armor layer. The distribution of vertical velocity shows that the strength of downfall velocity is the greatest under rough ice cover. Empirical equations were developed to estimate the maximum scour depth around side-by-side bridge piers under both open-channel and ice-covered flow conditions.
Part of the book: Current Practice in Fluvial Geomorphology