Submarine buried pipelines are often laid in trenches backfilled with loose sandy soil, which is intrinsically prone to liquefaction. When liquefaction is triggered, the soil tends to behave as a viscous fluid with vanishing shear strength and very limited ability to restrain structural displacement, for instance during the occurrence of pipeline flotation. Recently, a 2D CFD-based approach for the analysis of pipe flotation in liquefied sand has been proposed by Pisano et al. (2020), in which soil reconsolidation effects are phenomenologically captured by considering rheological parameters that evolve in space and time as pore water pressures dissipate. Despite a remarkable agreement with experimental data from the literature, the complexity and computational costs of such approach may still hinder its applicability to pipeline engineering practice. To overcome this limitation, a simplified model is proposed herein, in which all the forces governing the motion of the pipe are expressed via simple analytical relationships. After thorough validation against 2D CFD results and relevant experimental data, it is concluded that the new simplified model largely retains the predictive capability of Pisano et al.’s framework in combination with negligible computational costs.@en

Submarine buried pipelines interact with shallow soil layers that are often loose and prone to fluidization/liquefaction. Such occurrence is a possible consequence of pore pressure build-up induced by hydrodynamic loading, earthquakes, and/or structural vibrations. When liquefaction is triggered in sand, the soil tends to behave as a viscous solid–fluid mixture of negligible shear strength, possibly unable to constrain pipeline movements. Therefore, pipelines may experience excessive displacement, for instance, in the form of vertical flotation or sinking. To date, there are no well-established methods to predict pipe displacement in the event of liquefaction. To fill such a gap, this work proposes a computational fluid dynamics (CFD) framework enriched with soil mechanics principles. It is shown that the interaction between pipe and liquefied sand can be successfully analyzed via one-phase Bingham fluid modeling of the soil. Postliquefaction enhancement of rheological properties, viscosity, and yield stress can also be accounted for by linking soil–pipe CFD simulations to a separate analysis of the pore pressure dissipation. The proposed approach is thoroughly validated against the results of small-scale pipe flotation and pipe dragging tests from the literature.@en

This paper concerns the rheological characterisation of liquefied sands as non-Newtonian Bingham fluids. For this purpose, dam-breaking laboratory tests are often executed and interpreted, offering a viable option to identify the properties of fluidised water-soil mixtures. However, limited attention has been devoted so far to clarify what variables and measurements would allow unambiguous calibration of Bingham parameters, namely, the viscosity η and the yield stress τ _y . The numerical results of parametric studies based on the particle finite element method (PFEM) are critically inspected to gain deeper insight into the problem. First, it is confirmed that multiple η − τ _y pairs may reproduce the same experimental evidence when formed by only one measurement—usually, the post–dam-breaking displacement of the bottom toe (tip) of the liquefied mass. Then, two alternative procedures are proposed for unambiguous identification of both η and τ _y : one is based on monitoring the evolving aspect ratio of the fluid mass during free, gravity-driven flow; the other relies on a slightly different dam-breaking test, also including impact against a rigid obstacle. In particular, the latter approach reduces the relevant duration of the test, reducing the possible influence of reconsolidation effects on the calibration of rheological parameters.

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Submarine buried pipelines may often interact with shallow layers of loose sand that are particularly prone to liquefaction. When liquefaction is triggered by environmental loading and/or mechanical vibrations, the soil tends to behave as a viscous solid-fluid mixture and the pipeline to undergo either flotation or sinking. While a few indications can be found in the literature on the triggering condition for flotation/sinking, no conclusive methods are available to estimate the displacement of the pipe when liquefaction cannot be avoided. This preliminary work shows that combining in numerical simulations fluid and soil mechanics may successfully serve such a goal. The proposed modelling approach is compared to the results of small-scale pipe flotation tests, with emphasis on existing knowledge gaps and indications for future research on the subject.@en