Geotechnical seismic isolation (GSI) is a new concept that has been proposed recently. The injection of polyurethane into the soil layer (non-intrusive GSI) reduces seismic fragility without altering the original structure, which may provide an effective seismic isolation solution for existing bridge structures. The purpose of this study was to investigate the seismic isolation effect and isolation mechanism of non-invasive GSI applied to existing bridges. First, a noninvasive GSI site modeling method is described based on the results of existing soilpolyurethane resonance column tests and the OpenSees computational platform. Subsequently, a refined dynamic analysis model of site-existing bridge interactions was established by combining the rusting theory. The seismic isolation effect of the non-invasive GSI and its effect on the seismic response of the bridge were explored using a nonlinear dynamic time-course analysis. The results showed that non-invasive GSI soils can change the characteristic period of ground motion, thus reducing the site effect. The seismic isolation effect was positively correlated with the percentage of injected polyurethane. Altering the characteristic period of the site and avoiding as many of the preeminent periods of ground motion as possible is the result of noninvasive GSI. The non-invasive GSI soil layer reduces the structural response and provides seismic isolation throughout the life cycle of corroded piers, and its fragility is significantly reduced. Especially, the old piers have significant seismic isolation effect, effectively limiting serious damage or even collapse under earthquakes. The results of this study provide a reference for noninvasive GSI design of existing bridge structures.

Seismic isolation aims to prevent the direct transmission of seismic wave energy to the main resistant structure. Typically, this is achieved by using a flexible support system that isolates the base of the structural system from the ground, absorbing the relative deformation at the soil-structure interface. Meanwhile, the main structure tends to move as a rigid body on this flexible support. This article proposes an alternative approach for the dynamic characterization of shredded rubber, which is used in geotechnical seismic isolation (GSI). Traditional testing methods are expensive and require specialized equipment, making them less practical for routine determination. The article details the most important parameters needed to evaluate the applicability and effectiveness of the material in the context of GSI. The parameter of interest, i.e. the transverse elasticity module GR, was calibrated numerically from an experimental model of a column of shredded rubber subjected to free vibrations tests. The results were consistent with those obtained from resonant column and hollow cylinder tests. In this way, it is shown that the presented approach is capable of providing valid estimations of the transverse modulus of elasticity of shredded rubber.

Geotechnical seismic isolation (GSI) is a new category of low-damage resilient design methods that are in direct contact with geomaterials and of which the isolation mechanism primarily involves geotechnics. Various materials have been explored for placing around the foundation system in layer form to facilitate the beneficial effects of dynamic soil-foundation-structure interaction, as one of the GSI mechanisms. To reduce the thickness of the GSI foundation layer and to ensure uniformity of its material properties, the use of a thin and homogeneous layer of high-damping polyurethane (HDPU) was investigated in this study via centrifuge modelling. HDPU sheets were installed in three different configurations at the interface between the structural foundation and surrounding soils for realising GSI. It was found that using HDPU for GSI can provide excellent seismic isolation effects in all three configurations. The average rates of structural demand reduction amongst the eight earthquake events ranged from 35 to 80%. A clear correlation between the period-lengthening ratio and the demand reduction percentage can be observed amongst the three GSI configurations. One of the configurations with HDPU around the periphery of the foundation only is particularly suitable for retrofitting existing structures and does not require making changes to the structural systems or architectural features.