Large strain consolidation of clays: Numerical comparison between evaporation and electro-osmosis dewatering

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.