Advances in methodologies for seismic time history analysis for safety of offshore modular platform foundation in cohesive soil by 3D FEM

Abstract

The particular research presents dynamic time history analysis carried out for jack up spudcan foundation installed in the sea bed with varying soil parameters like undrained shear strength and stiffness of offshore cohesive soil with geometrical variations of jack up leg and spud angle. The entire study has been carried out using three-dimensional finite element-based software Plaxis 3D AE 2021 dynamic module. The motive of research is to study impacts of earthquake excitation with soil structure interaction through application of dynamic time history. The load deformation behavior is investigated under dynamic time history analysis. The same model is calibrated for various parametric studies under influence of earthquake forces. The versatile FEM techniques became very popular for studying earthquake impacts and dynamics soil -structure interaction phenomenon from last two to three decades. Impacts of frequency (fn), moment magnitude (Mw), embedment depth (Di), change in ratio of fundamental period to predominant period (Td/Tp), and changes of angle of internal cone of spud (A.I.C.S) with respect to seismic settlement have been studied. Research is enhanced to study influence of peak ground acceleration (PGA) and Arias Intensity on seismic settlement. Total 10 nos. earthquake records are selected whose epicenters are close proximity of offshore regions. Analysis results indicate that PGA and Arias intensity shows identical behavior at peak values and proportional to stiffness and undrained shear strength of offshore cohesive soil. When the angle of internal cone of spud flattens, amplitudes of displacements decrease. Increase in mass of leg or spud results into decrease of displacements.