Sustainable Marine Structures

Numerical Prediction of the Seismic Behavior of Offshore Skirted Foundations Accounting for the Separate Influences of Soil and Superstructure Inertia

Alaoua Bouaicha

Scientific and Technical Research Center on Arid Regions CRSTRA

Nassima Zatar

Civil Engineering Department, Faculty of Technology, University Mostafa Benboulaid, Batna 05078, Algeria

DOI: https://doi.org/10.36956/sms.v8i2.3300

Received: 4 May 2026; Published: 5 June 2026

Abstract

The seismic behavior of skirted foundations plays a crucial role in the stability of marine and coastal structures subjected to earthquakes. This study provides an in-depth examination of the seismic bearing response of skirted foundations subjected to eccentric vertical loading, assessed through a Finite Element Limit Analysis (FELA) framework. The objective is to separately characterize the inertial contributions of the soil mass and the superstructure as functions of the horizontal seismic coefficient kh, the relative skirt depth D/B, and the eccentricity ratio e/B. Unlike previous studies, which generally consider inertial effects in a simplified or combined manner, this work introduces a systematic and explicit separation of soil and superstructure inertia contributions for skirted foundations within a unified numerical framework, particularly under eccentric loading conditions. This approach enables a clearer distinction between local soil failure mechanisms and global structural effects, thereby improving the understanding of the seismic response of skirted foundations. The findings reveal the decisive role of skirt embedment depth, which enhances stability and delays failure, whereas increasing kh and e/B significantly reduces the bearing capacity. The resulting three-dimensional surfaces offer a clear visualization of the combined influence of these parameters, revealing critical operational zones and stability domains of skirted foundations under seismic loading. Two new generalized analytical equations were developed for the correction factors associated under inertial effects, showing excellent agreement with the FELA results. These formulations, combined with the developed 3D surfaces, provide practical and reliable tools for optimized seismic design of skirted foundations under seismic conditions.

Keywords: Eccentric Loading, FELA, Skirted Foundations, Seismic Bearing Capacity, Soil and Superstructure Inertia

References