Abstract:

To effectively address the undrained contraction problem of a cylindrical cavity in unsaturated soils, an auxiliary variable approach without simplifying the deviatoric stress and axial stress in the plastic zone is adopted. This approach is based on the modified Cam Clay model considering suction hardening and a liquid phase equation. The incremental governing equations of the stress component, matric suction and void ratio in the cylindrical cavity plastic zone are then derived according to the associated flow rule, the logarithmic large deformation geometric relation, and the equilibrium equation. Finally, the undrained solution of cylindrical cavity contraction in unsaturated soils is iteratively achieved from the initial value condition at the elastic-plastic interface, while validations and variations of the proposed solution are discussed. The results indicate that the proposed solution has important theoretical significance and good application prospect, because it reasonably accommodates comprehensive influences of cavity radius ratio, suction hardening and compactness, yet it is applicable to both hydrostatic and longitudinal uneven in-situ stress fields, and its parameters have clear physical meanings. In addition, the degradation, extension and application feasibility of the proposed solution are verified by comparing it with analysis results of the existing methods in many aspects. The tangential effective stress increases radially first and then decreases, and it reaches a peak at the elastic-plastic interface, whereas the matric suction and void ratio decrease radially rapidly at the beginning and then change slowly. The plastic zone radius reduces with the increase the effect of suction hardening.

Key words: unsaturated soils, cylindrical cavity contraction, undrained condition, suction hardening, the auxiliary variable approach