Geotechnical seismic isolation (GSI) using gravel-rubber mixtures (GRM), as an energy dissipative horizontal layer, is a foundation system that can enhance the seismic resilience of low-rise residential buildings. This paper presents the results of a numerical study carried out to evaluate the seismic performance of a selected GSI(VRC40) system (having volumetric rubber content of 40%) and compare it to that of a standard foundation system placed on a compacted gravel layer (i.e., without rubber). To this scope, a 3-dimensional FE model is implemented in OpenSees and calibrated using experimental data. In the model, a 12 m × 6 m × 0.5 m concrete raft foundation is placed on a layer of VRC40 with varying thicknesses (i.e., 0.6, 1.2, 1.8, 2.4, 3.0 and 3.6 m). No structures are considered in this study. The model is subjected to a ramped sinusoidal input base acceleration (ab = 0.1 - 0.5 g) at different frequency levels (f = 1 - 8 Hz). The accelerations at the base (aGIS,base) and top (aGIS,top) of the GSI layer are measured and it is found that the seismic performance of the GSI system significantly increases with increasing ab and f, as well as the GSI thickness, as the GSI(VRC40) layer is able to drastically reduced the acceleration transmitted at the GSI top (i.e., at the base of the concrete raft) as compared to that of the non-isolated gravel foundation. Using a recently proposed GSI efficiency index (EGSI), the effect of the thickness on the energy dissipation efficiency of GSI(VRC40) systems is further examined and it is found that GSI(VRC40) layers of 1.2‒1.8 m thicknesses represent cost-effective foundation systems to significantly reduce the seismic load on/improve the seismic performance of low rise-residential buildings.