Shaking table experiments on framed structure resting on geogrid reinforced geotechnical seismic isolation system

Seismic protection of buildings using the Geotechnical Seismic Isolation (GSI) system placed between the natural soil and the building foundation has recently emerged as an innovative and economical alternative to the traditional base isolation system. The present study aims to experimentally investigate the effectiveness of the GSI system composed of horizontal layers of Sand Rubber Mixture (SRM), a high damping energy-absorbing material reinforced with geogrids for seismic protection of mid-rise buildings. A series of 1-g laboratory shaking table tests were carried out on a five-story model framed structure placed on the GSI system in a laminar shear box filled with sand subjected to input excitation of 0.1 Hz to 10 Hz frequency range. The shake table tests were carried out under different base conditions of model structure: (1) pure sand, (2) SRM-GSI system and, (3) geogrid reinforced SRM-GSI system. The seismic performance of the model structure was compared for test beds with and without the GSI system by evaluating and analysing the recorded acceleration-time histories. The results indicate that while both SRM-GSI and geogrid reinforced SRM-GSI system effectively reduces the acceleration response of the buildings; however, the geogrid reinforcement was highly effective in reducing vertical ground settlement and contributing to improved lateral stiffness compared to the SRM-GSI case. The introduction of the geogrid reinforced SRM-GSI system tends to reduce the lateral displacements on the superstructure by 35%, besides minimizing the foundation rotation. In addition, the geogrid reinforced SRM-GSI system significantly reduces the interstorey drift of the model framed structure. Overall, the effectiveness of the geogrid reinforced SRM-GSI system in reducing seismic damages and permanent displacements of typical mid-rise buildings was experimentally demonstrated in the present study.