Alternative Method for Estimating Liquefaction-Induced Settlement of Shallow Foundation PLEM Using Finite Element Analysis

Abstract Settlement of subsea structures, such as Pipeline End Manifolds (PLEMs), is typically calculated using conventional software or analytical methods for non-liquefied soil conditions. However, these methods do not effectively address realistic structural settlement behaviors under liquefied soil conditions induced by seismic activities. Recent publications have introduced simplified procedures for estimating liquefaction-induced settlement, but these are tailored primarily for onshore structures and do not extend to subsea applications. Additionally, specialized software in geotechnical engineering has limited capability to model the penetration of shallow foundation structures through liquefied soil layers during seismic conditions. This study proposes an alternative method using Finite-Element-Analysis (FEA) to model and analyze the settlement of subsea structures, specifically PLEMs, in liquefied soil conditions caused by earthquake ground motions. The shallow foundation part of PLEMs, called mudmat, and soil layers were modeled. The soil model was defined based the density, the shear modulus, and pressure as a function of volumetric strain. The Smooth Particle Hydrodynamics (SPH) technique was employed to capture large deformations under dynamic conditions like earthquakes. Simultaneously, settlement of mudmat under the same conditions was reproduced using geotechnical engineering software to validate the proposed approach. The result from the studied FEA revealed greater settlement than traditional geotechnical engineering software in liquefied soil during seismic conditions. This comparison demonstrates the advantages and limitations of each approach, highlighting the enhanced capability of FEA when utilizing the SPH technique to capture the complex behavior of subsea structure in liquefied soils. Consequently, it provides more realistic results for design proposes.