## 4 Experimental Results  
### Compaction Properties of GRMs  
For satisfactory performance of structures made of soil-rubber assortments, it is necessary to properly control the compaction and correctly evaluate the physical properties of compacted materials. For the GRMs investigated in this study, vibratory table tests were found to be ineffective due mainly to the low moduli and energy absorption ability of  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{**Symbol**} & \multicolumn{4}{c}{**Grain Size (mm)**} & \multicolumn{2}{c}{**Specific Gravity**} & \multicolumn{2}{c}{**Dry Unit Weight, \(\gamma_{\text{d}}\)**} \\ \cline{3-6}  & & \(D_{\text{max}}\) & \(D_{\text{50}}\) & \(G_{\text{s}}\) & \(\gamma_{\text{d,min}}\) & \(\gamma_{\text{d,max}}\) \\ \hline Gravel & G & 10 & 6 & 2.71 & 15.4 & 17.2 \\ Large rubber & RL & 8 & 4 & 1.15 & 5.0 & 6.4 \\ Small rubber & RS & 4 & 2 & 1.14 & 4.2 & 5.9 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Index properties of the tested materials.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multirow{2}{*}{
\begin{tabular}{c} _VRC_ \\ **(\%)** \\ \end{tabular} } & \multicolumn{5}{c}{**Test Type**} \\ \cline{3-6}  & & **1-D** & **Direct** & **Bender** & **Cyclic** & **Batch** \\  & & **Compression** \# & **Shear** \# & **Element** \# & **Triaxial \#** & **Leading \#** \\ \hline G & 0 & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\circ\) \\ G-RL & 10 & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\circ\) \\ G-RL & 25 & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\circ\) \\ G-RL & 40 & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) & \(\bullet\) \\ RL & 100 & \(\bullet\) & \(\bullet\) & N/A & N/A & \(\circ\) \\ G-RS & 10 & \(\bullet\) & \(\bullet\) & N/A & N/A & \(\circ\) \\ G-RS & 25 & \(\bullet\) & \(\bullet\) & N/A & N/A & \(\circ\) \\ G-RS & 40 & \(\bullet\) & \(\bullet\) & N/A & N/A & \(\bullet\) \\ RS & 100 & \(\bullet\) & \(\bullet\) & N/A & N/A & \(\circ\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Summary of geo-environmental tests carried out in this study.  
the rubber aggregates. In contrast, Proctor compaction tests resulted in a suitable testing procedure, even if the moisture content was not a controlling factor. On the other hand, the minimum unit weight was simply attained by cautiously pouring the materials in the compaction mold with nearly zero depositional height. Typical results are reported in Figure 4a in terms of dry unit weight variation with \(V\!RC\).  
As the rubber particles are much lighter than the gravel ones (Figure 4b), both the minimum and maximum dry unit weights of GRMs decrease almost linearly by increasing \(V\!RC\). It is worth mentioning that, at \(V\!RC\leq 40\%\), the dry unit weight values of G-RS were slightly above the linear trends. This is because at lower \(V\!RC\) values, small rubber particles can easily occupy the large voids between gravel grains (Figure 4c), which results in an increase in the density state of the mixtures [39; 40; 41]. In contrast, because the size of RL particles is almost similar to that of the gravel, the rubber particles cannot fit in the voids between the gravel grains, even at lower \(V\!RC\), but rather replace the gravel grains in the mixtures. For completeness, a schematic illustration showing idealized packing density arrangements between gravel and RL and RS particles is reported in Figure 4c for \(V\!RC=20\%\) and \(40\%\).