ADVANCES IN RESEARCH WORK REGARDING IMPACTS OF BRIDGE PIERS ON ICE ACCUMULATION AND LOCAL SCOUR PROCESSES

River ice is an important factor affecting alluvial channels in winter. The appearance of bridge piers in channel changes the flow condition, and therefore affects the accumulation or ice jam process around bridge pier. On the other side, under ice-covered conditions, due to the extra boundary imposed by ice cover, the location of the maximum flow velocity is closer to the riverbed. Consequently, the riverbed scour around bridge pier under ice cover should be greater than in the absence of ice cover. By means of mechanical analysis of the stability of ice jams around bridge piers, a formula has been proposed to assess the stability of ice jams under the influence of bridge piers. The calculated results using the proposed formula were in good agreement with those measured in laboratory. Experiments have been conducted to study the impacts of bridge piers on the initiation of an ice cover. A formula for determining the critical concentration of ice floes on water surface for initiating an ice cover around bridge piers was developed. The proposed equation has been validated by data collected in laboratory and natural rivers. The relevant research works with respect to the local scour process around bridge piers/bridge abutments under both open flow and ice-covered (ice-jammed) flow conditions have been carried out in laboratory. Considering different bed material, pier size and ice-cover roughness, empirical formulas have been developed to calculate the maximum scour depth in the vicinity of bridge piers under ice-covered condition. Laboratory experiments have been conducted to study the local scour process around bridge piers under the ice-jammed flow condition. Results show that, under an ice-jammed flow condition, the local scour depth around bridge piers is much more than that under a sheet-ice-covered flow condition. Also, the bed deformation interacts with ice accumulation; namely, the thicker the ice jam, the more the scour depth, and vice versa. Under an ice-jammed condition, both the maximum depth and length of scour holes around a bridge pier increase with the flow velocity. Also, the height of a deposition dune downstream of a scour hole is affected by flow velocity This paper also summarizes further research work that needs to be carried out in the future.