Author(s): Titi Sui; Wujie Chen; Chi Zhang; Jinhai Zheng; Zhiyong Zhang; B. Mutlu Sumer; David R. Fuhrman
Linked Author(s): Jinhai Zheng
Keywords: Local scour; Submarine pipeline; Shell-sand mixture; Equilibrium scour depth; Flume experiment
Abstract: The stability of submarine pipelines in complex geological environments is the primary guarantee for the safe operation of marine projects. Comprehensive understanding of the local scour mechanisms beneath pipelines with shell-sand non-uniform seabed is crucial for the correct installation and maintenance of submarine pipeline projects. By conducting a two-dimensional flume experiment, a sediment mixture comprising fine sand with a median particle size (d50) of 0.20 mm and shell sand with a median particle size (d50) of 2.67 mm was employed to investigate variations in local equilibrium scour depth and scour morphology beneath submarine pipelines under steady current. The results illustrate that the equilibrium scour depth below the pipeline under steady current will decrease with the increase of shell sand content (SC). Results indicate that the consideration of a shell-sand mixture bed would induce bed surface "coarsening" during the scour process, contributing to enhanced bed stability and reduced equilibrium scour depth around the pipeline. Employing dimensional analysis, this study proposes a rational formula for predicting the scour depth of pipelines with shell-sand seabed which takes the Shields number, embedment and shell sand content into account: Se/D = Φ(θ/θc) ∙Λ(e/D) ∙Γ(SC), with 1 ≤θ/θc≤4, 0 ≤e/D≤0.3,0 ≤SC≤0.3 where: Φ(θ/θc) = tanh [0.1(θ/θc+ 1.15)2] Λ(e/D) = 1.04exp[−0.07(e/D)] Γ(SC) = 1.2exp (−2.1SC) The correlation coefficient between the predicted scour depth and the measured data reaches 0.79. For the engineering practice, the shell sand mixing proves effective in safeguarding pipelines from erosion, and an increase in the Shields number (flow intensity) would need
Year: 2024