# Investigation of Geotechnical Seismic Isolation Systems Based on Recycled Tire Rubber-Sand Mixtures
## 4 Conclusions and Recommendation
When evaluated in terms of economic and sustainability aspects, the numerical analyses conducted in this study, combined with the experimental results reviewed in the literature, suggest that isolation layers composed of rubber-enhanced sand (5-10% rubber) and pure sand provide a cost-effective and sustainable seismic isolation solution. However, higher rubber content may negatively affect soil stability, increasing deformation risks. Thus, the careful optimization of rubber content is crucial during the design phase. The increase in the thickness of the isolation layer significantly reduces amplification ratios. Generally, as the thickness of the seismic isolation layer increases, the damping ratio also increases. However, it has been observed that 1 m thick isolation layers are more effective in preventing seismic loads from being transmitted to the structure compared to 2 m and 3 m thick isolation layers. This is because the damping ratios provided by thicker isolation layers do not increase proportionally; instead, their effects are characterized by relatively smaller increments. Based on the results for isolation layers of 1 m, 2 m, and 3 m thickness, the percentage reductions in the peak accelerations of the soil response spectrum are as follows as shown in Table 16:  
It has been observed that isolation layers influence the natural frequency and amplitude behavior of the soil. The natural frequency of the untreated clay soil with a shear wave velocity of 200 m/s was measured to be 2.5 Hz. However, based on the results of applying isolation layers of 1 m, 2 m, and 3 m thickness, the natural frequencies of the soil were determined as follows as shown in Table 17. \begin{table}
\begin{tabular}{c c c c} \hline
**Earthquakes** & **1 m** & **2 m** & **3 m** \\ \hline
10\% rubber at 50 kPa & \%6.8 & \%6.87 & \%6.09 \\
10\% rubber at 100 kPa & \%7.41 & \%8.98 & \%10.53 \\
5\% rubber at 50 kPa & \%8.31 & \%10.57 & \%12.46 \\
5\% rubber at 100 kPa & \%8.64 & \%11.87 & \%14.33 \\
0\% rubber at 50 kPa & \%9.27 & \%13.92 & \%14.96 \\
0\% rubber at 100 kPa & \%9.43 & \%13.17 & \%16.17 \\ \hline \end{tabular}
\end{table} 
Table 16: The percentage of reductions in the peak accelerations of the response spectrum. Numerical analyses conducted using DeepSoil software were found to be in strong agreement with experimental results. The experimental findings indicated that reducing the rubber content under low confining pressures led to more controlled and reliable dynamic behavior. Rubber-enhanced soils, produced using recycled granular rubber materials, offer an economic and environmentally friendly solution. These materials, particularly when considering budget constraints in developing countries, stand out as an innovative seismic isolation approach for several key reasons:  
Granular rubber is derived from recycled materials such as discarded vehicle tires. This not only addresses waste management challenges but also promotes a sustainable construction approach by reducing environmental impacts. Repurposing end-of-life tires into valuable materials minimizes landfill requirements and decreases the risks of environmental pollution. Recycling rubber materials helps conserve raw material resources. This reduces the risk of depleting natural resources and promotes a sustainable circular economy model, ensuring the efficient utilization of materials. Conceptualization, D.S. and M.T. ; methodology, D.S. and M.T. ; software, D.S. ; validation, D.S. ; formal analysis, D.S. ; investigation, D.S. ; resources, D.S. ; data curation, D.S. ; writing--original draft preparation, D.S. ; writing--review and editing, D.S. ; visualization, D.S. ; supervision, M.T. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. All data are included in this article. The authors would like to thank [PERSON] for his support during this study. The authors declare no conflicts of interest.