Local scour around a bridge pier under ice-jammed flow condition – an experimental study

Abstract

The appearance of an ice jam in a river crucially distorts local hydrodynamic conditions including water level, flow velocity, riverbed form and local scour processes. Laboratory experiments are used for the first time here to study ice-induced scour processes near a bridge pier. Results show that with an ice sheet cover the scour hole depth around a bridge is increased by about 10% compared to under equivalent open flow conditions. More dramatically, ice-jammed flows induce both greater scour depths and scour variability, with the maximum scour depth under an ice-jammed flow as much as 200% greater than under equivalent open flow conditions. Under an ice-jammed condition, both the maximum depth and length of scour holes around a bridge pier increase with the flow velocity while the maximum scour hole depth increases with ice-jam thickness. Also, quite naturally, the height of the resulting deposition dune downstream of a scour hole responds to flow velocity and ice jam thickness. Using the laboratory data under ice-jammed conditions, predictive relationships are derived between the flow’s Froude number and both the dimensionless maximum scour depth and the dimensionless maximum scour length.

Simulation Study on Local Scour Characteristics of Tandem Bridge Piers in a Straight River under a Changing Environment

“…Figure 18 shows the comparison of scour hole slope between two scouring states in the scouring equilibrium stage, both of them have relatively steep scour holes along the front of the pier, while the slope at the end of the pier is gentle and the tail area shows a dune accumulation pa ern, in which under the clear-water scouring condition, the gradient of the flush pit of the front pier undercut by the water flow (straight line A1B1 inclination in the diagram) is about 29°, and the gradient of the flush pit on the pier side (straight line C1D1 inclination in the figure) is about 30°. The gradient of the flush pit of the front pier undercut by the water flow (straight line A2B2 inclination in the figure) is about 23°, and the gradient of the flush pit on the pier side (straight line C2D2 inclination in the figure) is 24°; by comparison, it was found that the slope is smaller than the repose angle of the submerged sediment of 32°, indicating that the quasi-equilibrium scour hole has reached a stable state [45].…”

“…Figure 18 shows the comparison of scour hole slope between two scouring states in the scouring equilibrium stage, both of them have relatively steep scour holes along the front of the pier, while the slope at the end of the pier is gentle and the tail area shows a dune accumulation pattern, in which under the clear-water scouring condition, the gradient of the flush pit of the front pier undercut by the water flow (straight line ; by comparison, it was found that the slope is smaller than the repose angle of the submerged sediment of 32 • , indicating that the quasi-equilibrium scour hole has reached a stable state [45].…”

Impact of Local Scour around a Bridge Pier on Migration of Waved-Shape Accumulation of Ice Particles under an Ice Cover

“…Wang et al [5] pointed out that the development of an ice jam can be divided into following three stages: the initial development of an ice jam from downstream toward upstream of a channel (stage 1); the formation of an initial ice jam along the entire channel (stage 2); and the thickening process of the initial ice jam accompanied by the migration process of ice waves (stage 3). During the third stage, the incoming ice particles from the upstream section will be entrained by flowing water and submerged and accumulated under the initial ice jam and gradually transport downstream.…”

“…When a bridge pier is present in a river, the pier affects the transport capacity of ice particles and floes, the thickness of ice jams, and the water level around it. In the meantime, the appearance of an ice jam results in intense local scour around piers [5]. The presence of scour holes around bridge piers changes the flow structure and influences the migration of the ice wave process around bridge piers.…”

“…The maximum scour depth increased with the increase in the roughness of an ice cover. Wang et al [5] analyzed the local scour under an ice-jammed flow condition through laboratory experiments. Results of these experimental studies show that the size of a scour hole is affected by the dynamic process of the accumulation of an ice jam, namely, the variation of the thickness of an ice jam around bridge piers influences the local scour process.…”