# Investigation of Geotechnical Seismic Isolation Systems Based on Recycled Tire Rubber-Sand Mixtures
###### Abstract  
In geotechnical earthquake engineering, enhancing the seismic properties of foundation soil to modify the characteristics of earthquake waves transmitted to structures presents a viable solution. This study investigates the effect of placing an isolation layer, composed of a mixture of recycled tire rubber and sand, beneath structures to mitigate seismic forces acting on buildings situated on soil layers with high amplification potential. In other words, the role of a soil layer functioning as a seismic isolator is examined. To achieve this objective, the seismic behavior of building-type structures is analyzed through numerical simulations, supplemented by laboratory experiments available in the literature. The numerical analyses are performed in the frequency domain using the finite element method within a one-dimensional (1D) framework. To validate the feasibility of the proposed isolation layer based on parametric analysis results, comparisons are made with laboratory tests available. In the literature, seismic isolation applications with thicknesses ranging from 1 to 3 m resulted in reductions of 6.8% to 16.17% in response spectral accelerations measured at the surface, while improvements in Fourier amplitude ratios ranged between 12.03% and 13.98%. This approach aims to provide an economical and efficient solution for earthquake-resistant structures while simultaneously promoting sustainability by recycling waste tires, contributing both to environmental conservation and economic benefits. s 2025 15 2133  
been met with excitement and enthusiasm, particularly in countries that regard and experience earthquakes as existential threats, owing to its cost-effectiveness and simplicity of implementation [2]. The fundamental principles of GSI are derived from traditional isolation systems, which typically consist of flexible or sliding interfaces placed between the foundation and vertical load-bearing elements to decouple the structure-foundation interaction. To put it succinctly, these systems separate the lateral movement of the ground from the structure, thereby reducing earthquake-induced shear and torsional forces on the building, making it more resilient against seismic events and their consequent deterioration [3]. In friction-based systems, synthetic layers are customarily used as isolators. The primary objective of using these layers is to create a stable isolation layer where a fraction of the seismic energy generated by earthquakes is dissipated through friction between the two materials. In damping-based systems, one or more improvement techniques are applied beneath the foundation to enhance the damping capacity of the underlying soil, thereby creating a geotechnical isolation layer focused on damping. This layer absorbs a portion of the earthquake's energy, thus reducing the amount of energy transmitted to the structure. In synthetic liner ground isolation method, referred to as ground isolation, a smooth synthetic liner is placed within the soil at a depth beneath the foundations to prevent seismic energy from reaching the building or ground surface. This approach isolates the soil layer above the liner from the underlying soil layer [4]. In damping-type geotechnical seismic isolation, energy dissipation is one of the primary mechanisms for reducing seismic ground motions. Rubber is known for its excellent energy absorption capabilities; hence, it is widely used in applications such as vibration control and damping in automotive parts. Rubber and soil particles complement each other functionally. Compared to conventional soils, rubber-reinforced soil demonstrates a significant increase in shear strength [5] and, more importantly, a substantial enhancement in energy dissipation capability. From a sustainability perspective, the reuse and recycling of waste tires are preferred over energy recovery. Tire fragments can be utilized in civil engineering applications such as road embankments, landslide stabilization, and as backfill material for retaining walls and bridge abutments.