Numerical investigation into the vulnerability to liquefaction of an embedded pipeline exposed to ocean storms

Abstract

This paper presents a numerical investigation into the vulnerability to liquefaction of an embedded pipeline exposed to ocean storms. In this study a series of irregular waves similar to a real ocean storm were generated using the JONSWAP spectrum, and their motions with the presence of ocean currents are described using the Reynolds-Averaged Navier–Stokes (RANS) equations. Under storm waves and currents, the dynamics of a seabed with an embedded pipeline were reproduced using a coupled fluid-dynamic framework. An advanced constitutive model (modified Pastor-Zienkiewicz Mark-III) was used to describe the cyclic plasticity of soil. This model was calibrated according to the given soil properties; the predicted results match the wave flume test and geotechnical centrifugal test fairly well when the evolution of residual pore water pressure near the pipe and/or further away are considered. The numerical results indicated that seabed soil is more susceptible to liquefaction due to regular waves than irregular waves. The specific gravity of the pipe can significantly affect the onset and spread of liquefaction in the neighbouring region. As a practical guide, a relationship between the critical wave height and the depth to which the pipe is buried is proposed to control the liquefaction at the bottom of the pipe by selecting feasible backfill materials based on operational requirements and ocean storm conditions.