## 3 Results and Analysis
### Stress-Strain Behavior under Different Stress Paths  
Figure 6 presents the variations of deviator stress \(q\) and volumetric strain \(\varepsilon_{\mathrm{s}}\) in response to shear strain \(\varepsilon_{\mathrm{s}}\) for the soil under 3 or 4 consolidation pressures. For all stress paths investigated in this study, there is no distinct drop of deviator stress after peak points in the \(q\)-\(\varepsilon_{\mathrm{s}}\) curves, which reflects the strain-hardening behavior of the UGRS. The shear strain corresponding to peak deviator stress is defined as failure strain. It is found that the failure strain increases with the increase in consolidation pressure regardless of stress path. Similar test results were reported by [PERSON] [50] for compacted decomposed granite soil. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Test Type**} & \multicolumn{2}{c}{**Strength Parameters**} \\ \cline{2-3}  & \(c\) **(kPa)** & \(\varphi^{\prime}\) **(degrees)** \\ \hline ICU & 14.9 & 28.2 \\ ICD & 47.8 & 28.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Strength parameters of the isotropically consolidated UGRS. Figure 6: _Cont._  
The volume change behavior of the soil strongly depends on consolidation pressure, as expected. When \(\alpha=56.3^{\circ}\), steady volume contraction is developed until the \(\varepsilon_{\rm{v}}\)-\(\varepsilon_{\rm{s}}\) curve reaches a plateau. The effects of consolidation pressure on the volume change behavior under \(\alpha=71.6^{\circ}\) and \(90^{\circ}\) are identical: while contractive behavior followed by volume dilatancy is observed under low consolidation pressures, volume dilatancy at large shear strain is suppressed when high consolidation pressures were used. Similar results appear in tests with \(\alpha=123.7^{\circ}\) and the volumetric strains at the end of test of soil specimens under \(\sigma_{3c}=100\), \(200\), \(300\) and \(400\) kPa are \(-2.82\%\), \(-0.62\%\), \(-0.10\%\) and \(0.32\%\), respectively. The mean effective stress remains unchanged when \(\alpha=90^{\circ}\); therefore, only the increment of deviator stress is responsible for the considerable volumetric strains developed, a large proportion of which is irreversible. In other words, deformation of the soil is the result of the coupled effects of mean effective stress and deviator stress; the UGRS shows a coupled and irreversible response, which cannot be represented by uncoupled models such as the simple linear elasticity, to stress path testing. For the case where \(\alpha=251.6^{\circ}\) (i.e., extension tests), besides the aforementioned inhibitory effect of high consolidation pressure on volume dilatancy, it is surprising that soil specimens develop appreciable volume contraction at the beginning of the test. Due to the fact that the increment of mean effective stress \(\Delta p^{\prime}\) is negative in this situation, the result above indicates the initial shear-contraction behavior of the UGRS under this stress path. In order to investigate the influence of stress path on the stress-strain behavior of the UGRS, the \(q\)-\(\varepsilon_{\rm{s}}\) and \(\varepsilon_{\rm{v}}\)-\(\varepsilon_{\rm{s}}\) curves of soil specimens under the same consolidation pressure but different loading angles are provided in Figure 7. Stress paths make a significant difference to the deformation characteristics of the UGRS. As can be seen, a considerable decrease in failure strain is observed as the loading angle increases for compression tests with \(\alpha=56.3^{\circ}\), \(71.6^{\circ}\), \(90^{\circ}\) and \(123.7^{\circ}\) under the same consolidation pressure. This observation will be discussed later in this section in a quantitative manner. As for the volume change behavior, the role of the stress path is evident: soil specimens show less volume contraction as the loading angle increases. For the same increment of deviator stress \(\Delta q\), the corresponding increment of mean effective stress \(\Delta p^{\prime}\) decreases and even becomes negative as the loading angle increases.