Seismic isolation effect of rubber-sand mixture cushion under different site classes based on a simplified analysis model

Abstract

The use of rubber-sand mixture (RSM) cushion in geotechnical seismic isolation (GSI) systems is an emerging technique for protecting buildings in earthquake-prone areas. The advantage is that RSM with high shear resistance and low shear modulus improves the foundation soil, allowing seismic energy to be partially dissipated in the cushion before it is transmitted to the structure. However, the isolation effect of the RSM cushion considering site classification has not been recognized due to the complexity of the problem. In this paper, a simplified analysis model is established to study the seismic performance of the RSM cushion, in which 195 ground motion records are obtained from different site conditions according to the Code for Seismic Design of Buildings GB50011-2010, reflecting the influence of site classification. By using the developed theoretical analysis method, the seismic isolation effect of the RSM cushion under different site classes is investigated. The key influencing factors to be considered include the cushion thickness, base pressure and seismic excitation intensity. The results show that: 1) The isolation effect of the underlying RSM cushion on the superstructure is affected by site classification. The harder the site, or more specifically, the shorter the predominant period of the site, the better the isolation effect of the RSM cushion. 2) For the same site classification, the isolation effect increases with increasing cushion thickness, base pressure and seismic excitation intensity. In particular, the robustness of the seismic performance of the RSM cushion deteriorates upon reaching a cushion thickness of 500 mm, and this deterioration in robustness is independent of site classification. Overall, the present study is the first systematic analysis of the effects of ground motion on GSI systems with RSM as the core under different site classes, and the research findings are of great significance for the low-cost seismic design of residential houses in developing countries.