Sacrificial piles as a countermeasure against local scour around underwater pipelines

Local scour around pipelines crossing rivers or in marine environments is a significant concern. It can lead to failure of the pipelines resulting in environmental side effects and economic losses. This study developed an experimental method to reduce local scour around pipelines with a steady flow of clear water by installing cylindrical and cubical sacrificial piles. Three sizes of sacrificial piles were examined in a linear arrangement. Sacrificial piles were installed on the upstream side of the pipeline at three distances. Maximum scour depth reduction rates below the pipeline were computed. The results showed that sacrificial piles could protect a pipeline from local scour. A portion of scoured sediment around the sacrificial piles was deposited beneath the pipeline. This sediment accumulation reduced the scour depth beneath the pipeline. Analysis of the experimental results demonstrated that the size of piles (d), the spacing between piles, and the distance between the pipe and piles (X_p) were the variables that reduced the maximum scour beneath the pipeline with a diameter of D. For the piles with d = 0.40D and 0.64D, X_p = 40D was the optimal distance to install a group of piles, and cubical piles could mitigate scour more effectively than cylindrical piles under similar conditions. For the piles with d = D, the greatest reduction in scour depth was achieved at X_p = 50D with any desired spacings between piles, and cylindrical piles in this dimension could protect the pipeline against scour more effectively than cubical piles.