Shaking table tests on geotechnical seismic isolation of electrical transformers using recycled tire rubber-soil mixtures

Electrical transformers were repeatedly damaged in recent earthquakes, leading to significant disruptions to energy infrastructure. This study introduces an innovative approach of geotechnical seismic isolation (GSI) by using rubber-soil mixtures (RSM) which incorporate recycled tire rubber for mitigating seismic responses of electrical transformers to both horizontal and vertical ground motions. The use of scrap tires as the rubber component in RSM can also support the green transition in construction materials by recycling waste. In previous studies, the mechanism of the GSI system has been explained and its effectiveness in structural demand reduction has been demonstrated through analytical and numerical studies. However, experimental validation through shaking table testing on this innovative isolation system has been limited, and its adoption on industrial facilities has not been reported. In this study, shaking table test was carried out to investigate the performance of GSI-RSM system for protecting Ultra High Voltage (UHV) electrical transformers on shallow foundations. The bushings on a transformer are usually made of brittle porcelain material, and they have different fundamental frequencies, allowing evaluation of the performance of GSI-RSM system on a wide range of natural frequencies. It was observed that the reduced horizontal and rotational stiffnesses of the RSM foundation are the key attributes to isolation effectiveness. Results showed that GSI system could achieve an average of 35 % reduction of strain response, which is the most important performance indicator for the bushings of the transformer. Significant reductions were also observed in displacement and acceleration responses. It is noteworthy that the performance was comparable when vertical excitation was also applied. A numerical model employing solid elements with equivalent linear viscoelastic properties for the RSM was developed to simulate the shaking table tests, achieving satisfactory agreement with the experimental results. • Geotechnical seismic isolation (GSI) using rubber–soil mixtures (RSM) is proposed for electrical transformers in substations. • Shaking table tests showed a reduction of seismic responses by an average of 35 %. • 3D numerical modeling of the GSI-RSM system closely matched test results. • Use of scrap tires in RSM supports the green transition of construction materials.