We present the results of a large-scale experimental campaign performed on the prototype structure of EuroProteas in Thessaloniki, Greece, to assess the effectiveness of gravel-rubber mixture (GRM) layers underneath shallow foundations as a means of geotechnical seismic isolation (GSI). We found that the geotechnical seismic isolation of structures is optimized by increasing the rubber content of the soil rubber mixture up to 30% per mixture weight. Although the effectiveness of the GSI systems has been investigated numerically and in small-scale experiments, this paper seeks to fill the gap in the lack of full-scale experimental studies on this subject. Three soil pits were excavated and backfilled with GRM of different rubber content per weight to serve as foundation soil for the structure. A large number of instruments were installed on the structure, the foundation, the soil surface, and inside the gravel-rubber mixture layers beneath the foundation to fully monitor the GSI-structure systems' response in three dimensions. The experimental investigation included ambient noise, free-and forced-vibration tests. Our results showed that a geotechnical seismic isolation layer composed of a gravel-rubber mixture with 30% rubber content per weight effectively isolates the structure. Even 0.5m thickness (i.e., B/6 of the foundation width) of the GSI system is successfully cutting off practically all emitted waves at a (horizontal or vertical) distance of B/6 from the foundation. A significant reduction in the GSI-structure system's stiffness was apparent, leading to a rocking-dominant response. The rise in the system's damping and the substantial energy dissipation inside the GRM layer highlight its effectiveness as a geotechnical seismic isolation system.

Dynamic soil-structure interaction (DSSI) plays a fundamental role in many geotechnical and/or structural design situations, as clearly shown by the damage which occurred during several recent earthquakes (Kobe 1995; Koaceli 1999; Chi-Chi 1999; L'Aquila 2009). For a long time civil engineering researchers have devoted increasing attention to this subject. Thanks to their efforts, several technical regulations, such as EC8 (2003), have taken DSSI into account. However, many steps are still necessary in order to increase our knowledge regarding this complex phenomenon, as well as to make all the results achieved known to academics and practitioners. This paper presents the results of a shaking table test performed on a scaled physical model consisting of a 3-D steel frame resting on a bed of sand. The experimental results are compared with the numerical ones obtained using a sophisticated elasto-plastic constitutive model recently implemented in the FEM code utilised. The solution of geotechnical problems requires the use of appropriate constitutive models. Many interesting constitutive models have been developed, but only a few of these have been implemented into commercial numerical codes; which is particularly so when dynamic analyses are required. The described experimental results, as well as the comparison between them and the numerical results, allow interesting considerations to be drawn on dynamic soil-structure interaction and on its numerical simulation.

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