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...