Experimental And Theoretic Study On Electro-osmotic Consolidation Of Soft Clay Foundation

It takes a long time and even is difficult to improve low conductivity clay with conventional gravitational drainage methods based on mechanics such as vacuum preloading and preloading. Challenge is increasing while soft foundation was formed more and more by hydraulic filling recently. Compared with natural clay, dredger fill or dredged sediment has larger compressibility and smaller undrained shear strength. In the advances of ground improvement technologies electro-osmotic consolidation is much promising because its drainage rate is independent of clay particle size. However, the application of this method was limited by consolidation mechanism, design and calculating, energy demand and others. Research program was implemented to study electro-osmotic consolidation of soft clay.Electro-osmotic experiments program in the three different electrodes arraies was conducted in the laboratory firstly. The effect of supply voltage and soil salinity to electro-osmosis was studied through one-dimensional laboratory tests. Larger voltage leads faster drainage and lower energy efficiency. Clay salinity had a significant effect on the electro-osmotic consolidation. Consolidation in the feasible salty ground could gain the best result by the lowest energy consumption. Two-dimensional laboratory tests were conducted to reveal the effect of electrodes spacing to consolidation and the variation of clay properties in the space and time during dealing. Halving the spacing while keeping voltage gradient constant could enhance consolidation evidently. Saturated stage of clay was transformed gradually to unsaturated stage by electro-osmosis. The wettest part after testing might be between anode and cathode. Voltage profiles between annular electrodes were measured in the axisymmetric experiments and were proved to be dependent of dealing time and radial distance. The difference caused by electrodes shapes to consolidation was obtained after comparing tests under three different conditions. Voltage drop in the contact of soil and electrode varied with electrode shape and each shape had its strong point.Then the caiculation of electric field among electro-osmotic electrodes was studied. The calculated formula of electric field intensity among electrodes arrayed rectangular was proposed based on the assumption of homogeneous isotropic soil and ignoring the sectional dimensions of electrodes. Horizontal electric field intensity was decomposed and simplified considering the effect of adjacent electrodes. The intensity in the direction parallel to the beeline through anode and corresponding cathode could be assumed to even and the value equaled to the intensity in the centre of rectangle while the one perpendicular to it included effective part and ineffective part which was two isosceles triangles with the base being the distance between electrodes of the same polarity and the height being half its base.Then the consolidation theory of electro-osmosis was analyted. According to the voltage profile measured in the axisymmetric experiments, axisymmetric electro-osmotic consolidation theory was established base on the equal strain assumption and related theories which already existed. The analytic solutions for average excess pore pressure and radial average degree of consolidation in terms of stress were provided and so did the method of conversion from hexagonal array of electrodes to axisymmetric array. This theory could incorporate the coupling action of electro-osmosis and loading and the effect of soil-electrode contact. The results of parametric analysis showed that better consolidation effect can be gained by higher supply voltage and there was a range of appropriate ratio of electro-osmosis permeability coefficient to hydraulic permeability coefficient for axisymmetric electro-osmotic consolidation.The design method of electro-osmotic consolidation of soft clay foundation was suggested at last. An ameliorated design method of electro-osmotic consolidation of soft clay foundation was proposed after investigating the collected data and summarizing the influence factors of electro-osmotic consolidation finally. The difference between the method and existed ones was that the electro-osmotic treatment acceptability of sites was evaluated before calculating and electro-osmotic system parameters could be optimized during selecting. Evaluation and optimization can be finished easily using the tables offered. A classical case history was illustrated to confirm that this design method lead electro-osmotic consolidation to be more effective and more efficient.The present work would be useful to promote the application and research of electro-osmotic consolidation of soft clay foundation.