Scour problems at railway bridges on the Thompson River, B.C.

The paper describes the history of riverbed changes and associated pier foundation problems at a series of five bridges along the Canadian National main line in the Thompson River valley of British Columbia. Pier failures were experienced in past years at two of these bridges, and there is a long history of placing rock riprap to combat local scour. The riverbed consists mainly of a thin layer of coarse alluvium overlying consolidated silt and clay.Special investigations conducted for one bridge, including a hydraulic model study, are described in some detail, and various schemes considered for foundation upgrading are outlined. Details are given of a special form of scour protection apron that was installed at one pier.Some research and design implications of the cases described are discussed briefly.