Experimental Study On The Initiation Of Ice Jam Under The Condition Of Bridge Piers

The formation of ice jam is a natural phenomenon prevalent in cold regions. In early winter, with a sustained drop of air temperature, the ice floes are transported along with the water flow; when spring comes, the ice cover will break up into large ice blocks and drift downstream. The existence of the piers can alter the hydraulic and boundary conditions of the river, decrease the ability of ice transporting, in return, raise the possibility of ice jam formation in the river. The formation of ice jam always begins with the ice blocking in bridge piers. According to the different characteristics, the initial ice cover may be classified as flat freeze-up and upright freeze-up. Consequently, to study the initiation of ice jam under the condition of bridge piers has important significance for preventing ice jam flooding.Based on laboratory experiments, the mechanism of ice blocking under the condition of bridge piers has been studied. The result suggested that the ice floes might be blocked and form a stable structure at the water surface part of bridge piers when flat freeze-up is formed. For upright freeze-up, the flow velocity and floating ice area concentration should be greater, and the underwater part of bridge piers might obstruct the ice floes transport, thus the longitudinal blocking might be formed; Whether a river can form freeze-up depends on the floating ice area concentration, and there is a critical value. For flat freeze-up, the critical floating ice area concentration is independent of Froude number, while related to the relative size of ice floes to bridge opening, it is found that they have decreasing power function relationship. The formation of upright freeze-up needs higher floating ice area concentration and greater flow conditions. The critical floating ice area concentration is greatly influenced by flow condition, and increased with the Froude number.