Abstract: Soils are often in an over-consolidated state due to complex stress paths such as unloading and reloading in practical engineering and the existing models for the cavity expansion problem fail to reflect the dilatancy and softening characteristics of over-consolidated soils. To this end, a semi-analytical solution for cavity undrained expansion in over-consolidated soils based on UH model was solved by using similarity solving technique in combination with associated flow rule and large strain theory. The response of stress and excess pore-water pressure caused by compaction effect was analyzed and the applicability of UH model was discussed by analyzing the variation of soil stress path with different over-consolidation ratios (OCR). The results, including the stress distributions curves, the expansion-pressure curves, effective stress path and yield locus variation curves and the evolution of the potential strength during cavity expansion, shows that: (1) For the lightly over-consolidated, the excess pore-water pressure decreases monotonously along the radial direction in the plastic zone in which the pressure curve presents a "S" shaped trend and decreases gradually around the cavity, particularly negative pore pressure appears around the pore wall, with the increase of OCR. (2) With the increase of OCR, the convergence of pressure-expansion curves becomes slower. (3) In the process of the cavity expansion, the normally consolidated soil is always in the stage of contraction and hardening. While for the over-consolidated, it goes through critical state to dilatancy and hardening stage to critical state to shear contraction and hardening one. This paper not only enriches the application of similarity solving technique, but also provides a reference for calculation of bearing capacity of pile foundation in over-consolidated soil, prediction for surrounding rock deformation of tunnels and determination of in-situ test parameters.

Key words: over-consolidated soils, cavity expansion theory, similarity transform theory, UH model, semi-analytical solution