On stability improvement of gravity type onshore and offshore structures

A protective cushion layer sandwiched between a gravity type caisson and the surrounding soil can improve the seismic stability of the caisson. In this paper, an interaction model was developed for analyzing such structure under earthquake loading. Interfaces on either side of the cushion were modeled as elements of finite thickness having different stiffness and constitutive properties. Participation from each element of the interaction system was taken into the account by incorporating appropriate factors at the respective interfaces. Seismic analyses were performed on a gravity-type caisson subjected to an actual earthquake motion. Comparison of the analysis results with a similar caisson without any protective cushion showed that the use of cushion yields a significant reduction of seismic load on the structure.