## 4 Results and Discussion
### Distributions of Stress and Excess Pore Pressure around the Cavity  
The stress distributions along the radial distance, including the stress components \(\sigma^{\prime}{}_{r}\), \(\sigma^{\prime}{}_{\theta}\), \(\sigma^{\prime}{}_{z}\), mean effective stress \(p^{\prime}\), and deviator stress \(q\), as well as the excess pore pressure \(\Delta u\), are plotted in Figures 11 and 12. These stress distributions at the instant of \(a/a_{0}=2\) for \(R_{\rm s}=1.2\) and \(1.5\) were also compared with those for \(R_{\rm s}=1.0\) (i.e., the solution in [22]) to investigate the influences of the initial structure and the subsequent stress-induced destructuation. Note that, in these figures, the radial distance \(r\) is normalized by the current cavity radius \(a\), and then plotted in logarithmic coordinates to highlight the stress features near the cavity. From Figure 11, it can be seen that the distributions of \(\sigma^{\prime}{}_{r}\), \(\sigma^{\prime}{}_{\theta}\), and \(\sigma^{\prime}{}_{z}\) for \(R_{\rm s}=1.0\), \(1.2\), and \(1.5\) are consistent in the far field but have significant differences in the near field around the cavity. According to the stress state, three zones, i.e., the elastic zone, plastic zone, and critical state zone, can be generally defined around the cavity. For reconstituted soils (\(R_{\rm s}=1.0\)), \(\sigma^{\prime}{}_{r}\), \(\sigma^{\prime}{}_{\theta}\), and \(\sigma^{\prime}{}_{z}\) vary monotonously in the plastic zone with a decrease in \(r/a\), and tend to be constant in the critical state zone. For structured soils (\(R_{\rm s}=1.2\), \(1.5\)), \(\sigma^{\prime}{}_{r}\) first increases to a maximum value corresponding to the peak strength of structured soils, and then decreases gradually with a decrease in \(r/a\) until the value is the same as that for \(R_{\rm s}=1.0\). It can also be seen that the larger the \(R_{\rm s}\) that is adopted, the larger the magnitudes of \(\sigma^{\prime}{}_{\theta}\) and \(\sigma^{\prime}{}_{z}\) that are obtained in the plastic zone. However, the final critical state values are the same for structured and reconstituted soils, irrespective of the initial structure. The influences of soil structure on the development of the stress-state zones around the expanding cavity can also be seen in Figure 11. For normal consolidated reconstituted soils (\(R=1\) with \(R_{\rm s}=1.0\)), there is no elastic zone, as shown in Figure 11a. However, for structured soils (\(R_{\rm s}=1.2\), \(1.5\)), the elastic zone appears because of the partial 'false' over-consolidated behavior of structured soils. For all cases, it can be seen that, as \(R_{\rm s}\) increases, the position of the elastoplastic boundary gradually shifts to the left, the ranges of the plastic zone and critical state zone become narrow, and the critical state zone even disappears in some cases. Figure 10: Relationship between the effective internal cavity pressure \(\sigma^{\prime}{}_{a}\) and the cavity radius \(a/a_{0}\). Figure 12 shows the distributions of the mean effective stress \(p^{\prime}\), the deviator stress \(q\), as well as the excess pore pressure \(\Delta u\) around the cavity. It can be seen that, for reconstituted soils (\(R_{s}=1.0\)), \(p^{\prime}\) and \(q\) remain almost unchanged in the vicinity of the cavity wall, which indicates that the soils have reached the critical state. As \(r/a\) increases, \(p^{\prime}\) and \(q\) may increase or decrease in the plastic zone, which actually depends on the values of \(R\). For structured soils (\(R_{s}=1.2\) and \(1.5\)), \(q\) increases rapidly with a decrease in \(r/a\), and then decreases to a stable value with the destructuration of soils after reaching the peak value. The variations in \(p^{\prime}\) can be divided into two patterns, for normally consolidated and lightly over-consolidated soils (Figure 12a,b); \(p^{\prime}\) remains a constant in the elastic zone and decreases monotonously with the decrease in \(r/a\) during the plastic deformation.