Current induced scour development and countermeasures around river-crossing pipeline systems

Date

2025-7-9

Author

Melek, Abiddin Berhan

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River-crossing pipelines are used to transport oil, gas, or any fluid under a water body. They are usually buried in the river bed, can be laid on the bed, or elevated from the bed. Although the pipelines are buried in the sediment, the flow can cause scour around the pipeline, and as a result, the pipeline may come out of its buried condition. The scour development around river-crossing pipelines threatens the safety and structural stability of the system due to the loss of bed support. Therefore, it is an important phenomenon to predict the maximum scour depths under equilibrium conditions and scour propagation around the pipeline. The aim of this study is to determine the current induced scour depths, scour lengths beneath a river-crossing pipeline placed in various positions under clear water conditions, to propose appropriate countermeasures to overcome the excess scour process, and to investigate the interference between pipeline scour and bridge abutment/pier scour. For this purpose, a series of experiments were conducted in the laboratory to determine the equilibrium conditions, maximum scour depths, and time-dependent scour development. In line with the findings in the literature, the maximum scour depth observed in the experiments was approximately 1.5 times the pipeline diameter (i.e., 1.5D). An empirical equation was proposed for estimating the dimensionless equilibrium scour depth within the limits of this study. It was also observed that approximately 85% of the maximum scour around river-crossing pipelines was completed within the first 10 hours under experimental conditions. Furthermore, a series of experiments were conducted to evaluate the effectiveness of two countermeasures—geocell application and downstream weir installation—at critical scour levels. The results indicated that geocells can reduce the maximum scour depth by up to 48%, while downstream weirs can achieve a reduction of up to 36%. In addition, the interaction between scour around the pipeline and other river structures (bridge piers and abutments) was investigated. In cases where the pipeline must be placed near such structures, it is recommended to position the pipeline at least 6D downstream or, if upstream placement is unavoidable, at a minimum distance of 8D from the structure.

Subject Keywords

River-crossing pipeline system, Sediment transport, Equilibrium scour depth, Time-dependent scour, Scour countermeasure

URI

https://hdl.handle.net/11511/115524

Collections

Graduate School of Natural and Applied Sciences, Thesis