Abstract: The rate effect of cavity expansion is not only related to the drainage conditions of the soil surrounding the cavity, but also closely associated with the rate-dependent mechanical properties of the soil. Most existing cavity expansion theories primarily focus on the rate effect caused by partial drainage conditions, with little attention given to the combined influence of drainage conditions and the rate-dependent mechanical behavior of soil. By employing numerical analysis and utilizing the overstress elasto-viscoplastic (EVP) model, the study focuses on the partial drainage conditions during cylindrical cavity expansion. The analysis indicates that when only the effect of partial drainage conditions is considered, the total radial stress and shear stress decrease monotonically as the expansion velocity increases, and the expansion velocity ranging from 10⁻⁴ to 10⁻¹ mm/s has a small impact on the total radial stress during the initial expansion stage. When the effect of partial drainage conditions and rate-dependent behavior is considered simultaneously, the total radial stress and shear stress gradually increase with the increase of expansion velocity during initial expansion stage, which is consistent with the results of in-situ self-boring pressuremeter tests conducted on the Burswood clay and Zhanjiang clay. With the cavity expansion, the radial total stress and shear stress show a pattern of first decreasing and then increasing with the increase of expansion velocity. Sensitivity analysis of the soil's viscoplastic parameters (γ ^vp and η ) reveals that, for a given expansion velocity, the total radial stress, shear strength, and initial shear modulus gradually decrease as γ ^vp or η  increase, with the rate of decrease diminishing over time. The expansion velocity, permeability coefficient, and overconsolidation ratio of the soil significantly impact the drainage conditions at the cavity wall, while the influence of γ ^vp and η  is relatively minor. The drainage conditions of the soil can be assessed using a dimensionless velocity V, with values of V corresponding to partial drainage conditions ranging from 0.04 to 250. It is suggested that the time-dependent mechanical behavior should be considered when applying cylindrical cavity expansion theory to analyze geotechnical problems related to cohesive soils.

Key words: cavity expansion, partial drainage, clay, elastic-viscoplastic, constitutive model