Large‐scale field testing of geotechnical seismic isolation of structures using gravel‐rubber mixtures

Abstract

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.

Resonant Column Tests on Mixtures of Different Sands with Coarse Tyre Rubber Chips

“…Compared to pure sands, the results from these studies showed an improvement of damping ratio associated with a decrease in shear modulus. Large scale tests showed the effectiveness as a means of geotechnical seismic isolation (Pitilakis et al 2021).…”

Analytical design models for geotechnical seismic isolation systems

“…In the past one and a half decades, numerical simulations and analytical modelling have been conducted by various researchers to demonstrate the effectiveness of GSI systems (Tsang et al 2009(Tsang et al , 2012aPitilakis et al 2015;Anbazhagan et al 2015;Abdullah and Hazarika 2016;Brunet et al 2016;Dhanya et al 2020;Forcellini and Alzabeebee 2022). Experimental testing and field measurement have also been performed to confirm the isolation mechanism and to evaluate their performance (Kaneko et al 2013;Nikitas et al 2014;Nappa et al 2016;Tsiavos et al 2019;Tsang et al 2021;Pitilakis et al 2021). It comes to the stage when appropriate design models, procedures and guidelines are needed for systematic design in real applications (Tsang and Pitilakis 2019).…”

Field testing of gravel-rubber mixtures as geotechnical seismic isolation

“…Recently, the first large-scale field experimental study of the dynamic response of the EuroProteas prototype structure founded on GRM layers was performed (Pitilakis et al 2021). The experimental findings showed that a thin GRM layer with a height of 0.50 m, including 30% rubber content per mixture weight, could effectively isolate the structure from the foundation soil.…”