Pipeline flotation in liquefied sand: A simplified transient model

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.