# Compaction Characteristics and Mechanical Response of Gravel-Glass-Rubber Mixtures +
## 4 Experimental Results and Discussions
### Behavioral Zones for Compacted GGRM  
From a mechanical viewpoint, it is well understood that for GRM, the addition of rubber inclusions to gravel induces a drastic reduction in stiffness that can be associated with the low modulus and deformability of the rubber inclusions ([PERSON] et al., 2016; [PERSON] et al., 2017; [PERSON] et al., 2018). By examining the load-transfer mechanisms of the GRM tested by [PERSON] et al. (2016)--using a combination of numerical simulations (Discrete Element Method) and micro-mechanical analyses--[PERSON] et al. (2016) have identified three distinct material-like behavioral responses for GRM (Figure 17): gravel-like for 0.3 \(<R_{\mathrm{B}}\), dual (intermediate) behavior for 0.3 \(\leq R_{\mathrm{B}}\) \(<\) 0.6, and rubber-like behavior for \(R_{\mathrm{B}}\) \(\leq\) 0.6. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Mixture**}} & \multicolumn{4}{c}{**Experimental Data**} & \multicolumn{4}{c}{**Mohr-Coulomb (Equation (5))**} & \multicolumn{4}{c}{**Nonlinear Model (Equation (7))**} \\  & \multicolumn{3}{c}{\(\boldsymbol{\phi_{\mathrm{sec(peak)}}}\) (\({}^{\circ}\)) at \(\sigma_{\mathrm{n}}{}^{\prime}\)} & \multicolumn{3}{c}{(\(\boldsymbol{c}^{\prime}\) = \(\boldsymbol{c_{\mathrm{a}}}\)\({}^{\prime}\))} & \multicolumn{3}{c}{(\(\boldsymbol{c}^{\prime}\) = \(\boldsymbol{0}\))} & \multicolumn{3}{c}{\(\boldsymbol{\phi_{\mathrm{sec(peak)}}}\) (\({}^{\circ}\)) at \(\sigma_{\mathrm{n}}{}^{\prime}\)} \\ \(\boldsymbol{R_{\mathrm{B}}}\) & \(\boldsymbol{G_{\mathrm{L}}}\) & 30 kPa & 60 kPa & 100 kPa & \(\boldsymbol{\phi_{\mathrm{peak}}}\) (\({}^{\circ}\)) & \(\boldsymbol{c_{\mathrm{a}}}\)\({}^{\prime}\) (\(\boldsymbol{\mathrm{kPa}}\)) & \(\boldsymbol{\phi_{\mathrm{peak}}}\) (\({}^{\circ}\)) & 30 kPa & 60 kPa & 100 kPa \\ \hline  
\hline \hline \end{tabular}
\end{table} 
Table 3: Strength parameters for GGRM evaluated by different failure criteria. In stiff, gravel-like materials, the load-transfer mechanism is primarily governed by the interaction between gravel grains due to the limited amount of rubber inclusions in the mixtures; this leads to a stiff (brittle) mechanical response. Instead, in soft rubber-like materials, the load-transfer mechanism is due mainly to the interaction between rubber inclusions because of the limited amount of gravel grains in the mixtures; this leads to a soft (ductile) mechanical response. Additionally, in the case of dual (intermediate) materials, the strong force network responsible for the load-transfer mechanism is jointly shared between the gravel grains and rubber inclusions; this results in an intermediate stiff-soft (brittle/ductile) mechanical response. The test results reported in this study indicate that the mechanical response of GGRM (\(R_{\text{B}}\) = 0.4 and 0.55) is similar to that of GRM (\(R_{\text{B}}\) = 0.4 and 0.55); thus, the investigated GGRM can be considered intermediate materials whose mechanical response is expected to be in between that of the stiff gravel, crushable glass, and soft rubber (Figure 17 and Table 4). Specifically, the experimental data show that as \(G_{\text{L}}\) increases (i.e., glass replaces gravel in the mixtures), the stiffness of the mixtures gradually reduces, and compressibility increases, mainly due to glass crushability. That is, at lower \(G_{\text{L}}\), the mixtures transfer the load mainly through the gravel-rubber particle-to-particle contacts, while at larger \(G_{\text{L}}\), the load is transferred primarily through the glass-rubber particle-to-particle contacts. Therefore, there is a gradual transition in the material type, from stiff-soft mixtures to soft-crushable mixtures, as glass is added in the mixtures as a replacement for gravel, as shown in Figure 17. Table 4 provides a description of the behavioral types identified for GGRM.