Abstract
This paper presents a numerical study to investigate the seismic behavior of mudmat and caisson foundations supporting subsea structures, such as manifolds, in liquefiable sand. In seismic areas, substantial earthquake loads can be imparted to subsea structures during ground shaking, threatening their stability. In particular, soil liquefaction in sandy soil arising from strong ground motions could significantly influence the performance of subsea structures founded on liquefiable sand. The results of this study can provide a better understanding of the response of subsea manifolds in liquefiable soil during and after the earthquake. Three-dimensional, non-linear, dynamic analyses are performed using a finite difference scheme, and the ability of the model to reproduce the site response of a saturated sand deposit is assessed using the results of available centrifuge data. This study includes six computational models representing manifolds with different sizes and weights supported by caissons and mudmats in shallow and deep liquefiable sand subjected to moderate and strong earthquake shakings. The response is evaluated in terms of excess pore water pressure generated in the soil medium and displacements of the subsea foundation during and after the shaking. The results show that manifolds may experience considerable movement during liquefaction and post-liquefaction settlements. In addition, depending on the characteristics of the seismic motion and structural system, the manifold could also experience large tilting.
Highlights
Subsea production systems include a variety of structures and facilities varying in size and weight from relatively heavy wellhead trees to large manifolds and templates
Kaynia [1] presented a comprehensive study on the dynamic response of 4-pile, caisson and mudmat foundations for subsea facilities and the effect of soil-structure interaction and radiation damping on the seismic performance of these foundations
It can be observed that the excess pore pressure is lower inside the caisson which is believed to be due to the kinematic confinement provided by the caisson described above
Summary
Subsea production systems include a variety of structures and facilities varying in size and weight from relatively heavy wellhead trees to large manifolds and templates. Kaynia [1] presented a comprehensive study on the dynamic response of 4-pile, caisson and mudmat foundations for subsea facilities and the effect of soil-structure interaction and radiation damping on the seismic performance of these foundations. In this study, calibrated soil parameters were confirmed using element-level and centrifuge tests, and different model features including boundary conditions, mesh size, and large-strain were investigated They extended their research to the earthquake response of monopiles and caissons with various dimensions for large offshore wind turbines subjected to a combination of wind load and earthquake shaking [39]. The present study investigates the earthquake response of caisson and mudmat foundations supporting subsea manifolds in liq uefiable sand subjected to moderate and strong ground motions To this end, three-dimensional, non-linear dynamic analyses were carried out for a total of eleven cases using advanced numerical modeling. The structure was placed symmetrically on the foundation which minimized the tilt due to earthquake shaking
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