Evaluation of instantaneous impact forces on fixed pipelines from submarine slumps

Submarine landslide–pipeline interaction has received considerable concerns in the field of pipeline design and disaster prevention. The majority of recent studies focused on the impact of fluidized debris flows and mudflows with the low strength and high speed on pipelines. However, less attention is paid to those high occurrence submarine slumps with high strength and low speed, which is a common stage of submarine landslide. Submarine slumps with the dual properties of soil and fluid have nonlinear mechanical characteristics that depend on the shear rate; thus, it is difficult to evaluate the impact of submarine slumps on pipelines coupled with the ambient water interaction under a single mechanics framework. In this paper, a CFD method of incompressible two-phase flow is employed to study the instantaneous impact of submarine slumps with the shear rate effect on fixed suspended pipelines under the hybrid framework of soil and fluid mechanics. Compared with past studies where only the horizontal impact force is considered at the ideal condition, the horizontal and vertical impact forces are presented to reveal more real instantaneous impact and corresponding mechanism while considering complex two-phase materials (i.e., submarine slump and ambient water) coupled with the boundary effect of the seabed. In particular, the undrained shear strength model of submarine slumps has a significant effect, leading to a maximum of 50% increase in these impact forces. Furthermore, considering the initial undrained shear strength and shear rate effect parameter of submarine slumps, the method and equations to evaluate horizontal and vertical impact forces are established, which enrich the reference data for submarine pipeline design.