Large-scale field experiments on the geotechnical seismic isolation capability of gravel-rubber mixtures

We present the first large-scale experimental campaign performed on the prototype structure of EuroProteas in Thessaloniki, Greece, to assess the effectiveness of gravel-rubber mixture (GRM) layers placed underneath shallow foundations as a means of geotechnical seismic isolation (GSI). The paper aims to provide insight into the response of the GSI-structure systems in the forced vibration experiments. Three GRM with different rubber content per mixture weight (0%, 10%, and 30%) were used as foundation soil layers. Before the execution of the field experiments, laboratory tests were carried out to determine the physical, mechanical, and dynamic properties of the three GRM. A large number of instruments were installed to fully monitor the response of the structure and the GRM layer. An eccentric mass shaker applied harmonic forces at the top of the structure over a wide range of frequencies and force amplitudes. The field test results showed that a GSI layer of 0.50 m thickness composed of a GRM of 30% rubber content reduces the fundamental frequency of vibration of the GSI-structure system and thus its stiffness, whereas the structure tends to oscillate as a rigid body over soft soil. Additionally, the increased material damping of the mixtures leads to an increase in the system’s damping. Overall, the recorded motion at the top of the structure is effectively reduced indicating that a thin GRM layer of 30% rubber content per mixture weight can be an efficient and affordable seismic isolation scheme.