## 6 Conclusions  
For the problem of cylindrical cavity expansion in naturally structured soils, an undrained elastoplastic solution was presented by using the SCC model of Carter and Liu [37]. Although the flow rules in the SCC model follow the different forms during the hardening, softening, and crushing processes, a unified system of differential equations was established for the considered problem, which can be solved in a simplified procedure by introducing an auxiliary variable. The present solution was compared with the previous solutions in reconstituted and structured soils to show the validity and significances of this study. Subsequently, parametric studies were conducted to explore the characteristics of cavity expansion responses in the structured soils, and then the influences of structural parameters were investigated. Finally, the casing installation and in situ SBPM tests were analyzed using the present solution. The following conclusions were drawn:  
1. Because the initial structure and destructuration effects are sufficiently considered, the present solution is capable of capturing the typical mechanical responses of naturally structured soils around the cavity. With the increase of the initial structure, the yielding stress increases and the 'false' over-consolidated behavior is strengthened. Moreover, as a result of the destructuration, the soils with different initial structures will reach the same critical state when the structure is completely destroyed;
2. The soil structure has significant influences on the cavity responses. As the cavity expands, the effective internal cavity pressure and the deviatoric stress decreases rapidly once the peak values are reached, which can be attributed to the release of accumulated stress due to the degradation and crushing of the structure;
3. The present solution can evolve to the existing solution in reconstituted soils when the structural parameters are sufficiently small. Therefore, the present solution can be regarded as a unified solution for cavity expansion in structured and reconstituted soils;
4. Compared with the previous solutions, the present solution takes the destructuration into account and captures the softening behavior of natural soils well;
5. The simulations of the casing installation and in situ self-boring pressuremeter tests indicate that the present solution provides an effective theoretical tool for the analyses of practical geotechnical problems involving cylindrical cavity expansion.  
Figure 17: Comparisons of calculated and experimental results for the SBPM tests: cavity strain pressure on the inner borehole wall.  
**Author Contributions:** Conceptualization, Y.Z. and T.L.; methodology, Z.Z.; software, Z.Z. and S.X.; validation, Z.Z.; data curation, Z.Z.; writing--original draft preparation, Z.Z.; writing--review and editing, Y.Z. and S.X.; supervision, Y.Z. and T.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Foundation of China (Grant No. 41807242).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.