Pipeline Flotation in Fluidized Soils: One-Phase Modeling Across Liquefaction and Backfilling Scenarios

This paper presents a framework that combines the mechanics of soils and fluids to model the flotation of buried marine pipelines in fluidized soils, addressing two practically important scenarios: (1) pipe flotation through liquefied sand and (2) uplift induced by sand settling during trench backfilling. Although these conditions arise from different transient soil states, they pose similar risks to pipeline stability. A unified approach is proposed to assess pipeline–soil interaction under transient strength loss and gain. The study combines analytical and reduced-order numerical modelling to represent fluidized geomaterials through a Bingham-type rheology with parameters that evolve in time. For liquefied soils, pipe uplift following triggering events is analyzed by accounting for pore-pressure dissipation and reconsolidation effects. For settling backfills, time-dependent rheology is interpreted using Kynch-type sedimentation theory to describe the space–time evolution of buoyancy and drag forces. Within this framework, simplified engineering models are shown to reproduce observed pipe uplift responses with satisfactory accuracy. The results highlight that flotation risk is strongly controlled by the evolution of rheological parameters in space and time, both in liquefied soils and in non-consolidated settling backfills. The proposed framework enables interpretation of pipeline response in relation to key soil rheological properties, moving beyond empirical flotation thresholds and supporting more physically grounded assessments of uplift potential under transient soil conditions. While further work is required to standardize procedures for estimating rheological parameters, the framework provides a consistent basis for analyzing pipeline flotation across different fluidization mechanisms relevant to offshore pipeline design and operations.