Author(s): M. A. Hopkins; S. F. Daly; D. R. Shearer; W. Townsend
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Abstract: The Alaskan Department of Transportation is considering building a bridge crossing the Buckland River at Buckland, Alaska. The Buckland River, near the Arctic Circle, is usually frozen each year from October through May. The interaction of the river ice and the piers of the proposed bridge is an important consideration. During spring breakup of the river ice cover, the moving river ice can exert large forces on bridge piers. The piers may also reduce the ice transport capacity of the river and cause the ice to stop moving or jam. Ice jams can have a dramatic effect on the river flow by blocking the flow area of the channel cross section and reducing the flow capacity of the channel. There have been 18 recorded ice jam flooding events at Buckland since 1971. It is important that the piers of the proposed bridge do not increase the likelihood of ice jam flooding in Buckland. A three-dimensional discrete element model coupled with an unsteady channel flow model was used to simulate the effects of four different bridge pier designs on the ice transport at the proposed bridge location. Two ice states were used in the simulations. The first ice state was composed of circular floes with a uniform diameter of 3 meters packed into a dense configuration approximately 1–2 m thick covering about 800 meters of the channel from bank to bank. The second ice state was composed of large circular floes with diameters ranging from 15 to 60 meters with an areal concentration of 0.5. The interstitial area between the large floes was filled with two layers of smaller circular floes with a uniform diameter of 3 meters. Baseline runs were made without bridge piers for each ice state. The simulations provided estimates of forces and overturning moments for the four bridge pier designs as well as their relative likelihood of causing ice stoppage.
Year: 2002