Laboratory tests on adhesion reduction of clay soil by electro-osmosis method

XIAO Yuhao;LIU Cheng;HUANG Lin;LIU Lei;College of Civil Engineering,Nanjing Forestry University;

electro-osmotic adhesion reduction;;clay;;adhesion;;tapered electrode;;adhesion failure;;shield

As a kind of adhesion reduction method,the electro-osmosis method can quickly reduce the adhesion force,and provide a new idea for solving the problem of soil sticking and clogging of the cutter face during the shield tunneling.In order to study the influence of electro-osmosis on the adhesion force,the self-developed electro-osmosis device was used to measure the maximum value of adhesion force and the electro-osmotic adhesion reduction under different moisture contents and continuous tensile state throughout the whole test. The test results show that the adhesion value first increases with the increase in moisture content,and reaches the maximum one near the plastic limit moisture content,then decreases and becomes stable when the moisture is greater than the liquid limit. In this paper,four groups of remolded soil samples with characteristic moistures between liquid and plastic limits contents were studied,and the pull-out force value in the constant-speed drawing state increased almost linearly with the drawing time.Under the action of electro-osmosis,the reduction time of adhesion was affected by the moisture content and the initial adhesion value tested before. There was an inflection point,which makes adhesion reduction time increase slowly before the point and increase sharply after the point. The average adhesion reduction rate increases first and then decreases with the changes in moisture contents of the four groups of selected soil samples,then the maximum adhesion reduction rate occurs at the moisture of 27% and the adhesion reduction ratio of 0.4. After the cone was disengaged,the soil particles on the surface adhered uniformly,and with the increase in electro-osmotic time and the decrease in adhesion value,the sticky particles continued to decrease. This phenomenon appeared to be significantly different from normal conditions with more sticky clay particles or smooth surface. Based on the analysis of experimental phenomena and results,the adhesion failure occured in the soil surrounding the water film at the interface,and was affected by many factors. The water tension and cohesion in the soil were the two main factors to affect the adhesion,and together determined the position of the adhesion failure in the soil. According to the research results,it may provide a theoretical basis for the application of electro-osmosis adhesion reduction in engineering.