Mechanism of geotechnical seismic isolation system: Analytical modeling

The innovative concept of geotechnical seismic isolation (GSI) system with the use of a continuous layer of low-modulus materials, such as rubber-soil mixtures (RSM), surrounding the foundation of structure has attracted considerable research interest on its performance at both system and material levels, since it was first proposed over a decade ago. The performance of the GSI system has been studied through a number of numerical, physical and hybrid modeling techniques; but due to the complexity of the problem, the isolation mechanism has not been thoroughly investigated. Hence, this article aims at initiating this aspect of development. A simple and efficient lumped-parameter analytical model is developed for analyzing the dynamic soil-foundation-structure interaction (SFSI) of the GSI system. Considering the importance of various nonlinearities involved, a theoretical approach for estimating effective shear strain is derived for capturing the nonlinearity of subsurface materials by the equivalent-linear method. The effectiveness of the analytical model is then demonstrated through a representative case study, based on which the main features of the isolation mechanism are investigated. The seismic isolation capability of the GSI system is founded on the reduced lateral stiffness of the RSM layer and the lower modulus of RSM that reduces the rocking stiffness. The proposed system could take advantage of the rocking isolation mechanism with reversible foundation deformations due to the higher elasticity of the RSM material.