Abstract: The uncertainty of riverbed terrain changes caused by water scour poses a threat to the safe operation of river-crossing pipeline. In the aim of exploring the scour characteristics of exposed river-crossing pipelines under heavy block protection measures, a flume model test was carried out to investigate the influences of four factors, namely, length of heavy block, the spacing between heavy blocks, flow rate and water depth, on scour terrain and scouring depth of riverbed around the pipeline. The scouring process of underwater pipeline under the protection of heavy block can be divided into four stages: formation of scouring pits, suspension of heavy block on the upstream side, suspension of pipeline on the upstream side, and scour balance. The maximum scouring depth of pipeline is positively correlated with the flow velocity and the length of heavy block, but negatively correlated with the water depth and the spacing between heavy blocks. The functional relationship between the dimensionless scouring depth, the length of heavy block, the spacing between heavy blocks and Froude number is obtained by dimensional analysis method. The research findings could be a theoretical support for the design, construction, operation and maintenance of heavy block protection measures for underwater crossing pipeline.

Key words: exposed river-crossing pipe, heavy block, scouring terrain, scouring depth, flume model test