A Study On The Influence Factors And Novel Methods Of Soft Soil Improvement By Electro-osmosis Techniques

Since electro-osmosis technique can rapidly improve the shear strength of soft soil with low permeability,it can be widely used in the empirical applications.Based on the results of previous researches,this study developed two electro-osmosis experimental setups to conduct a series of electro-osmosis experiments,the aim of which is to investigate the influencing factors and improvement methods of electro-osmosis consolidation effect.The main contents of this paper are summarized as follows:Firstly,a vertical electro-osmosis experimental setup and a horizontal experimental setup were developed.The vertical setup can be easily manipulated to do decoupling analysis.The horizontal one can satisfy different experimental conditions with respect to solution type,contact of soil and electrodes,and drainage conditions.And it is used to test and compare different methods in improving soft soil in the electro-osmosis experiments.Moreover,a data collection system was developed to monitor and record the current,settlement,temperature,electrical potential distribution,and drainage volume during the experiments.The setups developed can not only satisfy the requirements of this research,but also provide some insights for other related researches.Secondly,the influence of durations,salt contents,electrode materials,clay types,voltages,temperatures,loading pressures,and drainage directions on electro-osmosis consolidation effect are fully investigated.It is found that horizontal shrinkage appears when the increment of effective stress resulted by the negative pore water pressure in the soil is greater than the critical value of K0 condition during the electro-osmosis experiments.And the horizontal shrinkage becomes larger with the experiment on;The performance of cupper anode heavily relies on the salt content in the soil.The higher salt content is,the heavier cupper’s corruption is,which makes the relative performance（compared with stainless steel anode）of cupper anode worse.The electro-osmosis permeability ke is proportional to zeta potential and porosity;The higher voltage is,the better electro-osmosis effect is.But higher voltage will produce more heat;Higher temperature can also improve the electro-osmosis effect;Finally,an ANN model was established to predict the water content of soil after electro-osmosis consolidation.Thirdly,in order to improve the electro-osmosis effect after cracks appear during the experiment,different methods were put forward.Inserting a relay anode into the crack can build a new electro-osmosis flow field between relay anode and cathode,thereby increasing the drainage volume of electro-osmosis experiments.Filling the crack with the graphite powder can increase the electro-osmosis channels,resulting an improvement of drainage volume.Moreover,avoiding the cracks during the electro-osmosis experiment is crucial.Adding enough polypropylene（PP）fiber into soil can increase the tensile of soil,thereby avoiding cracks.As a result,electro-osmosis consolidation effect is improved.Comparing with the methods mentioned above,the chemical injection method performs best,and has the potential to improve the soft soil uniformly.Finally,to improve the soft soil uniformly,this part fully explored the mechanism of electro-osmosis grouting of saline solution and put forward optimized procedures.Initially,settlement of consolidation and water content distribution were explained based on pore water pressure distribution formula obtained from mass conservation equation.Then this study found the improvement of soil near the cathode can be attributed to the cementation,which can be explained by ion migration theory.However,the cementation will decrease the electro-osmosis channels if it is produced too early.Therefore,the method of electro-osmosis grouting of saline solution should consider both of cementation ability and electro-osmosis drainage ability.Separating the electrode and soil can make more Ca²⁺ enter into soil,thereby promoting the cementation.Moreover,adding（NaPO3）6,which is a kind of retarder,can not only increase Ca²⁺ content in the soil,but also guarantee the electro-osmosis drainage ability.Based on the procedures above,an optimized time for injecting Ca²⁺（anode side）was determined.The result suggested that method of electro-osmosis grouting of saline solution performed best when Ca²⁺was injected in the first two days.