Undrained Solution for Cylindrical Cavity Expansion in Structured Clays Using a Hypoplastic Model

This paper develops an innovative undrained solution for cylindrical cavity expansion using a hypoplastic model that could well reflect the mechanical properties of clay, especially the structural degradation of unstable clay. Then, the constitutive relationship of the hypoplastic clay model for cavity expansion problems is established by adding the strain rate-displacement relationship in cylindrical coordinates. Therefore, simple first-order ordinary differential equations are obtained to solve the problem of cavity expansion for structured clay. This paper compares the proposed solution with the Abaqus finite-element solution and conducts an extensive analysis of the model parameters. The results prove that the solution can accurately capture the expansion responses under undrained conditions. The variations and distributions of the internal cavity pressure, excess pore pressure, and sensitivity in unstable structural clay are obtained, which show obvious trends of structural degradation. The normalized expansion pressure and excess pore pressure decrease as the value of OCR increases. The normalized cavity pressure and structural degradation radius decrease as the structural parameters increase, while the opposite change is observed in the excess pore water pressure. The results of the application analysis can be used as a reference for clarifying the variation in the bearing capacities of piles and the disturbance of surrounding soil in practical engineering.