Experimental Study On The Influential Factors And Improving Method Of Electro-osmotic Permeability Of Soft Clay

Electro-osmosis is considered to be a promising method to reinforce soft foundations. Widely distributed deep natural soft soils in waterfront area of China, and the increasing number of reclamation projects and environmental geotechnical engineering projects, all provede a good chance for electro-osmotic to develop.Electro-osmotic permeability is a basic parameter of electro-osmotic, however, there are a lot of contradictions in the research of electro-osmotic permeability. Therefore, it is necessary to do research on it systematically and comprehensively. In this thesis paper, three external factors and four intrinsic factors are chosen to study the influencing factors of electro-osmotic permeability, furthermore, a method to increase electro-osmotic permeability was attempted. Main research work and corresponding results are listed in what follows.(1) After summarizing exitiong researches, electric potential gradient, electrode materials, and electrode spacing were chosen to conduct single factor and one-dimensional electro-osmosis experiments and study how the external factors influence electro-osmotic permeability. It is found that external factors only change total electro-osmotic permeability, while have little influence in efficient electro-osmotic permeability. So it is considered that efficient electro-osmotic permeability reflects the intrinsic nature of soils.(2) At the basis of Helmholtz-Smoluchowski model, water content, salt species (to discuss pH value at the same time), salt content and humus content were considered to intrinsic factors which are influential to electro-osmotic permeability, so the single factor model tests of those factors were performed. It is found that, comparatively speaking, water content influences electro-osmotic permeability most, folloeed by salt content, while salt species (pH value) and humus content seem to have little influence upon electro-osmotic permeability. It is also found that there is critical water content, below which electro-osmotic permeability increasing as water content incrases, while above which electro-osmotic permeability staying almost steady. The critical water content of Hangzhou soft clay used in this thesis paper is about70%. At the range of water content experienced, the smallest electro-osmotic permeability is about50%of the biggest.(3) The applicability of electro-osmosis in practical projects was discussed from two aspects, including the effect of dewatering and the economic. It is considered to be practical to deal with clays with high water content, salt content lower than0.5%,and humus content lower than5%, but impractical in clays with salt content around or above2%, or humus content around or above20%. It should be considered seriously to deal with clays with medium salt content or humus content.(4) In order to improve the electro-osmotic permeability, flocculants were injected in labrotary experiments, the idea of which coming from the inspiration gained from Krishna R. Reddy’s research. However, electro-osmotic permeability doesn’t increase whatever flocculants, whatever the concentration, whatever the injecting place. The benefit is that the energy consumption coefficient decreases as flocculants injected. When the soluntion injected contains2%or5%polyacrylic, the energy consumption coefficient decrease by more than20percent.(5) The Helmholtz-Smoluchowski model was discussed. There are two questions considered to be existing in this model, which lead to ineffectiveness in predicting some experiment results, one for exaggerating the driving force of the fluid, the other for unsaturated soil being ignored.(6) In order to solve the problem of limited effects of deep soil using electro-osmotic method reported by scholars, the experiment of electro-osmosis combined with loading and pneumatic fracturing was conducted. The deep soil was better treated on the experiment of electro-osmosis combined with loading and pneumatic fracturing. The shear strength of the deep soil on the experiment of electro-osmosis combined with loading and pneumatic fracturing increases by34.6%compared to the experiment of electro-osmosis combined with loading. It provides a reference for the projects with high demand for strengthening deep soil.