Interaction of Pipeline and Saturated Sandy Seabed under Progressive Waves

ABSTRACT:The stability of pipeline in saturated sandy seabed is significantly influenced by wave-induced liquefaction. In most of the former numerical researches, the sandy seabed is considered as elastic material. However, it cannot simulate the accumulation of excess pore pressure and gradual changes of effective stresses under cyclic dynamic loadings like progressive waves. Based on previous work of writers’ research group, elasto-plastic analysis method which can indicate the progress of liquefaction is used to simulate the interaction of pipeline and saturated sandy seabed induced by waves. The results of numerical simulation show that liquefaction first occurs under the pipeline then transfers upward and simultaneously liquefaction occurs at seabed surface then transfers downward, eventually bring the entire sandy seabed around the pipeline into liquefaction; Under the pipeline, once liquefaction is generated, it delivers downward too; It is much easier for wave-induced liquefaction to happen when the sand is close to pipeline compared with the farther sandy seabed at the same depth; Under the action of progressive waves, the stresses of pipeline change considerably that tensile stress is formed and vertical stress increases dramatically under the condition of calculated waves which greatly threatens the safety of pipeline.

Key words: pipeline, saturated sandy seabed, liquefaction, progressive waves, elasto-plastic analysis