| A large number of engineering problems related to consolidation of marine sludge have emerged with construction and maintenance of port and coastal engineering. Traditional physical consolidation methods, such as preloading and vacuum preloading, are limited by low shear strength and low permeability of marine sludge. Electro-osmosis, short for EO, is more promising because its drainage rate has nothing to do with clay particles and buckling failure would not happen during electro-osmotic consolidation process. However, EO technology is not widely used mainly because of lack of electro-osmotic theory、complicated consolidation mechanis、large energy demand, and physical and chemical variance of soil may lead to completely different consolidation effects. So it is necessary of further EO test research on marine sludge to provide references for practical engineering.On the basis of one dimensional electro-osmotic relevant theories, a series of laboratory experiments of marine sludge in Dalian were conducted on self-made apparatus. Monitor and analyze drainage、electric current and voltage distribution during test process, electrode corrosion、water content and un-drained shear strength after test to research the influence of electrode material、electric potential gradient and preloading on electro-osmotic consolidation. Main conclusions were as follows:(1) Form microscopic perspective, EO method could reduce the thickness of diffusion layer in DDL (double diffusion layer) around clay particles and carried water molecules out through the ions movement, which was the advantage over traditional consolidation methods. Coefficient of electro-osmosis permeability mainly maintained the order of10"5cm2/(V. s), which was hardly affected by clay particles. One-dimensional EO consolidation theory could qualitatively describe the distribution regularity of pore pressure and consolidation process of soil. However, it was still necessary to study electro-osmotic drainage and reinforcement effect through specific EO experiments.(2) Ferrum electrodes made a better performance than cuprum and aluminum in electro-osmotic process, mainly because for ferrum electrode, effective potential and current decayed slower、ultimate drainage and consolidation effect were better. The main reason was that copper anode surface generated non-conductive CuCl (cuprous chloride) which could increased contact voltage losses between anode and soil、reduced effective potential and current, that leaded to poor reinforce effect and extra corrosion. When using aluminum electrodes, the reaction between electrolytic aluminum ion and sludge might produce low conductive soil that would lead to high strength near anode but general overall the specimen because of large consume of effective voltage. In addition, part of aluminum electrode would be dissolved in acid and alkaline environment around anode and cathode.(3) Voltage gradient impacted on EO obviously. Higher voltage gradient bought bigger current higher drainage rate and better consolidation effect, but anode corrosion and energy consumption would increase as well. Electrode materials and electric potential gradient weakly affected coefficient of electro-osmosis permeability, and the coefficient had a tendency to reduce for a long time.(4) The whole preloading has positive function on electro-osmotic drainage, including reduce of interface potential loss and increase of drainage rate, also the strength of soil near electrode increased significantly after electro-osmosis, but pressure on both ends could not improve drainage rate and ultimate displacement. The stability of reinforced soil was good because7days’strength and instant strength were similar, while the moisture content tended to be more uniform along with time. |
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