## 3 Test Results and Analysis  
### Deformation Characteristics of Rockfill Materials Considering the Effect of Density  
The deviatoric stress and volumetric strain versus axial strain curves for specimens with a relative compaction of \(D_{\mathrm{r}}\) = 0.60 under different confining pressures are shown in Figure 7. Five points, \(A\), \(B\), \(C\), \(D\), and \(E\), divide the loading process into five stages. Point \(A\) represents the initial yield with the beginning of the volume change; point \(B\) represents the phase change state with the beginning of the volumetric strain shift from shear contraction to shear expansion; point \(C\) represents the peak strength, indicating maximum volume compression (stress-strain hardening) or the fastest volume expansion (stress-strain softening) when the rockfill materials reach the limit of resistance to external forces; point \(D\) represents the critical state with gradual volume change tending to level off; and point \(E\) represents the end point of loading. When the confining pressure is low (\(\sigma_{3}\) = 300 kPa), the stress-strain relationship exhibits strain softening, as illustrated in Figure 7. As the axial strain increases, the deviatoric stress increases, with body shrinkage deformation due to the volumetric strain. When the axial strain is loaded to approximately 4%, the volumetric strain compression reaches the limit and transforms into volume expansion. At this point, the specimen is in the phase change state (point \(B\)). The specimen enters the damage state when the deviatoric stress reaches the peak (point \(C\)), and the body expansion deformation becomes more distinct. Furthermore, as the shear proceeds, the deviatoric stress starts to decrease and stabilize, along with the stabilization of the volumetric strain, which ultimately results in the critical state (point \(D\)). When the confining pressure is high (\(\sigma_{3}\) = 900 kPa), the stress-strain relationship shows strain hardening and the deviatoric stress increases with increasing axial strain, resulting in the corresponding shrinkage of the specimen's corresponding volume. The volumetric strain shows body shrinkage deformation, which continues until the end of loading. The deviatoric stress does not exhibit a peak during the loading process. At this point, the specimens' phase change, peak, and critical states occur in the same state (\(D^{\prime}\)). The confining pressure determines the deformation characteristics of specimens with distinct densities. The lower the confining pressure, the more distinct the strain softening phenomenon; the higher the confining pressure, the more distinct the strain hardening phenomenon. Figure 6: Laboratory test and numerical simulation curve. The deviatoric stress and volumetric strain versus axial strain curves for specimens with different densities at a confining pressure of 600 kPa are shown in Figure 8. When the relative density of the specimen is large (\(D_{\mathrm{r}}\) = 0.90), the stress-strain relationship exhibits a strain-softening relationship. As loading proceeds, the deviatoric stress increases initially, with body shrinkage resulting from volumetric strain. A loading of axial strain up to approximately 2% results in the phase change state of the specimen (point \(B\)) and the maximum compression value of the volumetric strain, which subsequently results in volume expansion. This is followed by a more noticeable body expansion deformation, resulting in the fastest volume expansion when the axial strain reaches approximately 5%. The deviatoric stress also peaks at this point, and the specimen reaches a limited resistance state to external forces. Furthermore, the deviatoric stress decreases and stabilizes at 18% of the axial change. The deformation of body expansion also slows down at this point, reaching a critical state (point \(D\)).