# Investigation of Geotechnical Seismic Isolation Systems Based on Recycled Tire Rubber-Sand Mixtures
## 4 Conclusions and Recommendation  
The results of this study reveal key differences and similarities with previous studies. While prior studies, such as those by [PERSON] [9], primarily investigated seismic isolation effects in controlled laboratory settings, the present study extends this analysis by incorporating real earthquake records and site-specific ground motion characteristics. The comparative analysis of Fourier amplitude spectra and damping behavior indicates that the inclusion of RSM significantly reduces peak accelerations, particularly in the horizontal direction, a finding consistent with the numerical studies of [PERSON] [11]. However, unlike previous research, which mainly considered shallow isolation layers, this study highlights the importance of confinement depth, demonstrating that the effectiveness of RSM increases with depth up to a certain threshold, beyond which additional thickness provides diminishing returns. Moreover, the present study challenges some earlier assumptions regarding the relationship between rubber content and damping capacity. While [PERSON] and [PERSON] [13] suggested a linear increase in damping with higher rubber content, our findings indicate a nonlinear trend where excessive rubber inclusion may lead to a decrease in damping efficiency at lower confining pressures. This discrepancy underscores the necessity of optimizing rubber content based on site-specific conditions rather than applying a uniform design approach. In summary, this study not only validates and extends previous findings but also introduces a novel approach for optimizing seismic isolation systems using RSM. By addressing limitations in prior research and presenting a comprehensive analysis of geotechnical seismic isolation, this study provides valuable insights for both theoretical advancements and practical applications in earthquake-resistant design. In this study, the seismic performance of granular rubber-sand mixtures were investigated. For this purpose, pure sand (0% rubber) and sand mixtures containing 5% and 10% granular rubber were utilized. The experimental results reviewed during the literature survey revealed that the seismic isolation performance of granular rubber-sand mixtures is significantly influenced by both the rubber content and the confining pressure. This observation was also confirmed in the numerical analyses conducted during the study, where it was determined that the damping ratio tends to increase as the rubber content in the isolation layer decreases. However, the literature review further highlighted that under higher confining pressures, such as 200-300 kPa, this trend is expected to reverse, as observed in experimental studies in Figure 1.  
In the study, it was observed that the damping ratio decreased as the rubber content increased under relatively low confining pressures (50 and 100 kPa). However, the literature review suggests that this trend is expected to reverse at higher confining pressures, such as 200-300 kPa shown in Figure 1. Given its potential to enhance performance and provide economic benefits, this phenomenon remains an open topic for more detailed investigations. In isolation layers formed with sand-rubber mixtures, it was observed that the damping ratio increased with confining pressure. Similarly, under the same loading conditions, analyses conducted for layers without rubber content revealed that the damping ratio also increased as the confining pressure increased. Rubber-reinforced soils demonstrated an enhanced damping capacity under dynamic loads. However, at low confining pressures, higher rubber content was found to reduce the elastic modulus, thereby negatively impacting soil performance. Under confining pressures of 50-100 kPa, the reduction in rubber content demonstrated a positive influence on isolation layers, effectively mitigating soil-structure interaction risks.