Hydrodynamic loads on tandem twin pipelines induced by submarine landslides: Insights from physical flume tests and SPH simulations

Submarine landslides impose extreme dynamic hazards on subsea pipelines. Research concerning the fluid-structure interaction between submarine landslides and tandem twin pipelines remains limited. In this work, flume model tests are performed using slurries consisting of sand, kaolin clay and water to reproduce landslide masses. A validated multiphase smoothed particle hydrodynamics (SPH) model is adopted to quantify the influences of landslide volume, slope gradient, solid mass fraction and pipeline geometry on impact loads and wake-shielding performance. The full landslide-impact process is categorized into four successive stages: initial collision, main peak loading, steady impact, and deposition dissipation. When subjected to submarine-landslide impact, the upstream pipeline generates a flow-blocking shielding effect for its downstream counterpart, delaying the downstream impact response and substantially lowering its peak impact load. At a solid mass fraction of 70%, the load reduction ratio attains 62.18% for an upstream-pipeline diameter of 30 mm and further rises to 85.47% at 50 mm. A critical “most unfavorable spacing” is identified; this characteristic spacing shift downstream from 250 mm to 350 mm as the landslide volume increases from 0.024 m 3 to 0.040 m 3 . The present findings provide theoretical references for disaster-resistant layout design of subsea pipelines.