# Compaction Characteristics and Mechanical Response of Gravel-Glass-Rubber Mixtures +
## 4 Experimental Results and Discussions
### Compression of Compacted GGRM Under One-Dimensional Loading  
The normal compression (virgin loading) response of GRM and GGRM obtained from 1D compression tests with creep is reported in Figures 6 and 7 (note that such normal compression curves have been extracted for the unloading/reloading compression tests that are reported in Figures 8 and 9). From Figure 6a, it is evident that the addition of rubber to gravel generates a much more deformable material (e.g., under 100 kPa vertical effective stress (\(\sigma_{\rm v}\)'), the gravel experiences approx. 1% volumetric strain (\(\epsilon_{\rm v}\)'), while those of GRM are on the order of \(\epsilon_{\rm v}\) = 9.5% and \(\epsilon_{\rm v}\) = 10.5% for \(R_{\rm B}\) = 0.4 and \(R_{\rm B}\) = 0.55, respectively). These test results are consistent with those reported by [PERSON] et al. (2017). Figure 6b,c indicate that the addition of green glass to GRM (\(R_{\rm B}\) = 0.4 and \(R_{\rm B}\) = 0.55) produces an increase in the 1D compression. Such an increase is proportional to \(G_{\rm L}\). Furthermore, GGRM with \(R_{\rm B}\) = 0.4 performed better than those with \(R_{\rm B}\) = 0.55 (i.e., a much smaller \(\epsilon_{\rm v}\) is developed under the same applied \(\sigma_{\rm v}\)'). For example, in the case of \(G_{\rm L}\) = 0.45, \(\epsilon_{\rm v}\) is 11.5% for \(R_{\rm B}\) = 0.4 and 19.1% for \(R_{\rm B}\) = 0.55, respectively. Figure 6: Normal compression response of GGRM in one-dimensional tests with creep: (**a**) gravel-rubber mixtures (\(G_{\rm L}\) = 0) (experimental data from [PERSON] et al. (2017) and this study); (**b**) GGRM with \(R_{\rm B}\) = 0.4 and (**c**) GGRM with \(R_{\rm B}\) = 0.55. Figure 7: Variation of the secant constrained modulus obtained from one-dimensional compression tests: (**a**) GGRM with \(R_{\rm B}\) = 0.4; and (**b**) GGRM with \(R_{\rm B}\) = 0.55 and gravel. Figure 7 shows the variation of the secant drained constrained modulus (\(M=\sigma_{\rm v}{{}^{\prime}}/\varepsilon_{\rm v}\)) with \(\sigma_{\rm v}{{}^{\prime}}\) for GGRM with \(R_{\rm B}=0.4\) and \(R_{\rm B}=0.55\). \(M\) of gravel is also reported for completeness. In a log-log plot, \(M\) increases linearly with increasing \(\sigma_{\rm v}{{}^{\prime}}\); however, it decreases with increasing \(R_{\rm B}\) and \(G_{\rm L}\). 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 particles. The data also suggest that as \(G_{\rm L}\) increases, GGRM stiffness gradually reduces, and compressibility increases, mainly due to glass crushability. Moreover, at lower \(G_{\rm L}\), the mixtures transfer the load mainly through the gravel-rubber particle-to-particle contacts, while at larger \(G_{\rm L}\), the load is transferred primarily through the glass-rubber particle-to-particle contacts. Therefore, there is a gradual transition in the material type, from hard-soft mixtures [54] to soft-crushable mixtures; that is, the more rubber and glass are present in the mixtures, the more compressible the material becomes, and thus the lower the \(M\). In Figures 8 and 9, the unloading-reloading 1D compression responses of GGRM are reported in terms of settlement vs. time and \(\varepsilon_{\rm v}\) vs. \(\sigma_{\rm v}{{}^{\prime}}\) relationships, respectively. A sudden initial (plastic) settlement can be observed for GRM, which is the result of the rubber particle deformability and the rearrangement of non-compressible gravel grains. When glass is added to the mixtures to form GGRM, the glass grain rearrangement and  
Figure 8: One-dimensional unloading/reloading compression response of gravel, GRM (\(R_{\rm B}=0.4\) and \(R_{\rm B}=0.55\)), and GGRM (\(R_{\rm B}=0.55\), \(G_{\rm L}=0.45\)). Figure 9: Variation of vertical strain in one-dimensional unloading/reloading tests with creep of GGRM with (**a**) \(R_{\rm B}=0.4\) and (**b**) \(R_{\rm B}=0.55\). crushing also play a key role, and a much larger initial settlement takes place (Figure 8).