Seismic dynamics of a pipeline shallowly buried in loosely deposited seabed foundation

It is widely known that submarine pipelines constructed in high seismic intensity zones are vulnerable due to soil liquefaction under the attack of seismic waves. It is meaningful for engineers to get insight into the seismic dynamic response mechanism of submarine pipelines, which mostly are buried in loosely deposited seabed floors in practical engineering. In this study, taking the integrated numerical model FSSI-CAS 2D as the platform, the seismic dynamic response of a shallowly buried submarine pipeline in a loosely deposited seabed floor is investigated. It is indicated by the numerical results that a shallowly buried submarine pipeline in loose seabed floor intensively responds to input seismic wave. Considerable vibration in horizontal and floatation in vertical occur for the pipeline due to the soil softening in the surrounding soil, as well as the soil liquefaction in the zone away from the pipeline. The buoyancy applied on the outer wall of the pipeline caused by the pore pressure accumulation makes a significant contribution to the upward floatation of the pipeline. It is found that the seismic wave-induced residual liquefaction firstly initiates in the medium depth of seabed floor due to the relatively great permeability of the loose seabed soil, and then develops toward to the upper and lower seabed synchronously. Because of the intensive interaction between the pipeline and its surrounding seabed soil, liquefaction has not occurred in the zone at the right and left-hand side of, as well as over the pipeline. Based on comparative analysis, it is found the magnitude of pipeline floatation if natural gas is transported is much greater than that if crude oil is transported. Finally, it is observed that considerable subsidence at the magnitude order of 1 m occurs for the pipeline in the post-reconsolidation process after seismic wave attacking. It is indicated by the analysis presented in this study that the integrated model FSSI-CAS 2D would be a trustworthy platform to study the seismic dynamic response of marine structures.

Automated summary

The study demonstrates that submarine pipelines buried in loosely deposited seabed floors exhibit significant dynamic response to seismic waves, including horizontal vibration and vertical floatation. The softening of surrounding soil and liquefaction in the soil away from the pipeline play a crucial role in the pipeline's response.