Consolidation of soft clay, clay slurry, or mine tailings takes a long time to complete, because of the very low permeability and high compressibility. When such materials are deposited over a wide area, consolidation naturally starts due to evaporation. Letting the soil consolidate under atmospheric evaporation is typically inexpensive in terms of energy input, but it might be time consuming and possibly inefficient. Among alternative techniques for accelerating consolidation, electro-osmosis is numerically analysed here, by means of a large strain coupled electro-hydro-mechanical finite element formulation including unsaturated flow.Volumetric strains and variation in the degree of saturation induced by changes in both hydraulic and electric driven pore water flows are accounted for. These, in turn, affect the transport parameters, which are assumed to depend on the degree of saturation and on the void ratio. Electro-osmosis consolidation and atmospheric evaporation are simulated for a soft clay layer, after calibrating the model against data from small scale laboratory tests. The efficiency of electro-osmosis consolidation compared to evaporation is demonstrated by the numerical results, which highlight the different water content, degree of saturation and stress state profiles resulting from the two different consolidation processes.

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This paper presents a numerical model for the elasto-plastic electro-osmosis consolidation of unsaturated clays experiencing large strains, by considering electro-osmosis and hydro-mechanical flows in a deformable multiphase porous medium. The coupled governing equations involving the pore water flow, pore gas flow, electric flow and mechanical deformation in unsaturated clays are derived within the framework of averaging theory and solved numerically using finite elements. The displacements of the solid phase, the pressure of the water phase, the pressure of the gas phase and the electric potential are taken as the primary unknowns in the proposed model. The nonlinear variation of transport parameters during electro-osmosis consolidation are incorporated into the model using empirical expressions that strongly depend on the degree of water saturation, whereas the Barcelona Basic Model is employed to simulate the elasto-plastic mechanical behaviour of unsaturated clays. The accuracy of the proposed model is evaluated by validating it against two well-known numerical examples, involving electro-osmosis and unsaturated soil behaviour respectively. Two further examples are then investigated to study the capability of the computational algorithm in modelling multiphase flow in electro-osmosis consolidation. Finally, the effects of gas generation at the anode, the deformation characteristics, the degree of saturation and the time dependent evolution of the excess pore pressure are discussed.

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A newly developed numerical model is used to identify and evaluate optimum electrode configurations for electro-osmosis dewatering, as well as to evaluate approaches such as current intermittence and current reversal. Various electrode configurations, electrode spacings, and voltage gradients are studied numerically using 3D models with a cubic domain and vertically installed tube electrodes. The results indicate that, with more anodes installed, one can expect more water to drain out and a more uniform surface settlement, although a greater energy consumption is then required. A 2D square domain is used to study current intermittence and current reversal. Current intermittence allows more water to be drained out and has a higher energy efficiency compared to a continuous current, although it consumes more energy. Polarity reversal is also shown to be more efficient than a continuous current supply.@en

In this paper, the nonlinearity of the gravelly and clayey soils in Japan is investigated based on the Kiban Kyoshin network (KiKnet) downhole array seismic observations. Shear modulus reduction ratios at 18 sites under 165 strong motions are calculated by comparing the response amplification spectra (surface response normalized by bedrock response) subjected to strong motions with those subjected to weak motions and are plotted versus the corresponding seismically induced shear strains. The back-calculated shear modulus reduction ratios are categorized into several groups under different effective confining pressures, and a best-fit line is proposed for each group as the corresponding empirical shear modulus degradation curve. The obtained results are compared with the existing studies based on both in situ and laboratory tests, highlighting the influence of different testing techniques on nonlinear soil behavior. Furthermore, a modified cyclic nonlinear model is used to formulate the proposed empirical curves to account for the shear modulus degradation under a wide range of effective confining pressure. This modified model can then be used to specify material constitutive relationships for the future numerical analysis of geotechnical structures under seismic loads.@en