Abstract: Electro-osmosis is frequently used in combination with surcharge loading in foundation treatment. Based on Fredlund’s three-dimensional consolidation theory of unsaturated soil, Esrig’s electro-osmosis consolidation theory and the equal-strain assumption, the governing equations of axisymmetric consolidation considering the radial-vertical flow and smear effect under the coupled electrical and flow field are derived. The semi-analytical solution in the time domain is obtained using Laplace transform, decoupling technology and Laplace inverse transform. Then, the solution of this paper is degraded to the two cases of considering the combined electro-osmotic and surcharge preloading in saturated soil and considering only the load in unsaturated soil respectively to compare with the existing solutions to verify the reliability of the solution in this study. Finally, the effects of the parameters such as effective voltage, electro-hydraulic permeability coefficient ratio, and smear coefficient on the axisymmetric consolidation characteristics of unsaturated soils are investigated by arithmetic examples. The results show that the negative pore pressure finally generated by excess pore-water pressure is proportional to the effective voltage; the consolidation of unsaturated soil under electro-osmosis and surcharge preloading can be divided into two stages, which are mainly affected by loading and electro-osmosis; the settlement of the foundation treated by electro-osmotic and surcharge preloading is the sum of the settlements when the two actions treat the foundation separately, and for the soil with low permeability, the consolidation rate will be significantly increased. Furthermore, the difference in the rate of excess pore-water pressure dissipation in the same interval of the smear coefficient after applying voltage is larger than that when voltage is not considered, and the smaller the smear coefficient is, the greater the negative pore-water pressure finally generates.

Key words: electro-osmosis, unsaturated soil, smear effect, time-varying load, semi-analytical solution