# Compaction Characteristics and Mechanical Response of Gravel-Glass-Rubber Mixtures +
## 5 Potential Use of GGRM as Fill Materials in Geotechnical Applications  
The prospect of mixing a variety of recycled materials, such as crushed glass and granulated rubber, with gravel holds practical significance. The results of earlier investigations on GRM indicate that such synthetic materials can be used as geomaterials and primarily as lightweight backfill materials, shallow underground layers for mitigation of liquefaction phenomena, and geotechnical seismic isolation for low-to-medium-rise lightweight structures/infrastructure [33; 34; 35; 36; 37; 38; 39; 40; 41; 46; 47; 48; 49; 50; 51; 52; 53]. Due to the many similarities between GRM and GGRM, it is therefore expected that compounds made of gravel, crushed glass, and granulated rubber will also have adequate strength, compressibility, and minimal leaching aspects, making them suitable geomaterials [57]. In previous studies by [PERSON] [58] and [PERSON] [59], GRM has been primarily studied and optimized to be used in geotechnical seismic isolation (GSI) foundation systems to increase the seismic resistance of lightweight residential buildings. The results of dynamic cyclic triaxial tests [60], impact hammer tests on a physical model [59], and advanced finite element numerical simulations [58; 59] have indicated that GRM (\(R_{\text{B}}\) = 0.4 and 0.55) can effectively filter the seismic waves passing through the GRM layer and reduce the seismic load transferred to the superstructure by 50% or more. Based on these findings, GS and potentially GSC mixtures may be used in GSI foundation systems. Overall, the investigated GGRM (\(R_{\text{B}}\) = 0.4 and 0.55) would have adequate strength (i.e., peak friction angle of 30\({}^{\circ}\) or greater) to be used as fill materials in eco-friendly geotechnical projects [38]. However, because of their high compressibility at low \(G_{\text{R}}\) values (i.e., for high combined \(G_{\text{L}}\) and \(R_{\text{B}}\) values) and the different mechanical behavior they can exhibit under applied loads (Figure 17), their use as structural fills may not always be feasible or may require some improvement, as indicated in Figure 18. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Symbol** & **Behavioral Type** & **Remarks** \\ \hline S & Soft & \(R_{\text{B}}\geq\) 0.6; rubber-like materials, the load-transfer mechanism is due primarily to the interaction between soft rubber inclusions \\ \hline G & Stiff & \(R_{\text{B}}\) \textless{0.3} and \(G_{\text{L}}\) \textless{0.3}; gravel-like materials, the load-transfer mechanism is due mainly to the interaction between stiff gravel grains \\ \hline C & Crushable & \(R_{\text{B}}\) \textless{0.3} and \(G_{\text{R}}\) \textless{0.3}; glass-like materials, the load-transfer mechanism is due mostly to the interaction between crushable glass particles \\ \hline GC & Stiff–crushable & \(R_{\text{B}}\) \textless{0.3}, \(G_{\text{L}}\geq\) 0.3 and \(G_{\text{R}}\geq\) 0.3; intermediate materials, the load-transfer mechanism is primarily shared between gravel grains and glass particles; rubber inclusions are mostly inactive \\ \hline GS & Stiff–soft & \(0.3\leq R_{\text{B}}\) \textless{0.6} and \(G_{\text{R}}\) \textgreater{0.4}; intermediate materials, the load-transfer mechanism is principally shared between gravel grains and rubber inclusions; glass particles are mostly inactive \\ \hline SC & Soft–crushable & \(0.3\leq R_{\text{B}}\) \textless{0.6} and \(G_{\text{L}}\) \textgreater{0.4}; intermediate materials, the load-transfer mechanism is mainly shared between glass particles and rubber inclusions; gravel grains are mostly inactive \\ \hline GSC & Stiff–soft–crushable & \(0.3\leq R_{\text{B}}\) \textless{0.6}, \(G_{\text{L}}\leq\) 0.4 and \(G_{\text{R}}\leq\) 0.4; intermediate materials, gravel grains, glass particles, and rubber inclusions actively and jointly contribute to the load-transfer mechanism \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Behavioral zones identified in this study for compacted GGRM.