Research Methods And Engineering Application On Electrokinetic Consolidation Of Soft Soil Foundation

Electro-kinetic consolidation(EKC),which is categorized as electro-osmotic consolidation(EC)and electro-osmotic chemical treatment(ECT),can be used to strengthen the soft soil.Due to the characteristics of the soft soil including high water contents,high compressibility,low bearing capacities,and low shear strengths,it is difficult for the traditional techniques to consolidate and strengthen.Compared with the traditional techniques,EKC is a promising and useful method for enhancing the mechanical properties of the soft soil and improve its strength as it shows many advantages,such as the increased consolidated speed,less chance to occur instability,and improved safety.However,EKC is developing slowly owing to several restraints,such as,imperfect introduction of consolidation mechanism for EKC,incomplete computation method,lack of design approach in the field,severe erosion of the electrode,etc.This paper summarized the development and researches of EKC,and introduced the double electronic layer theory which is the basis theory of EKC.Based on the researches and the experimental requirements for this paper,the mechanics of EKC was described.Also,one-dimension and two-dimension pore pressure of EKC and the stress-defined consolidation formula were proposed for this research.According to the theory and the engineering requirements,the design method had been improved to solve the issues shown in the engineering projects.In this research,a series of laboratory tests were conducted,numerical simulation and field tests were also performed based on the laboratory experimental results.The following results had been achieved in the research:1.Designed a laboratory experimental system.The EC tests under different potential gradients were conducted to analyze the effect of the potential gradient on consolidation.According to the distribution of the electrodes in practical engineering,the effect of the electrode groups were investigated to propose a new concept of electrode distance ratio which is defined as the ratio of the distance of adjacent electrodes with the same electrical polarity to the different electrical polarity.The optimal electrode distanceratio were obtained though the experimental results.2.Addressed the issue of the electrode erosion.A new composite electrode was developed in this research.It has been demonstrated that the carbon electrode is feasible for the EC,but it may crack with a high electric current.The new composite electrode which consists of carbon fiber,plastic drain board,and steel board was developed to improve better consolidation performance and reduce the electrode erosion.The comparison between the new composite electrode and the traditional steel electrode shows its feasibility for EC and gives the optimal potential gradient.3.The ECT tests were proposed to solve the existed issues in the EC tests.The results received from the single-electrode ECT were compared with the EC test,and the results showed that the bearing capacity of the soil was improved with the injection of the chemical solution.In the ECT tests,comparative analysis on the single and double injectionwas performed to demonstrate that the sodium silicate is effective to restrain the development of cracks of the soil.4.The change of the voltage was fitted with the data in the EC test with a single electrode.A simulation of electric potential field was performed by coding and computing.Based on this result,a simulation on a field test in Dalian City was performed to analyze the relation between the electrode distribution and the ultimate bearing capacity of the soil.According to the requirements of the simulation on voltage using Comsol,two groups of laboratory tests with two different draining directions were designed and conducted,and a series of simulation was performed based on the laboratory tests.The filed study in Dalian City was analyzed further using the simulation results to provide a robust description of the consolidation in the field study.The simulation results are useful to adjust the electrode distances and the number of electrodes and to develop the reasonable design approach for various field studies.5.This research investigated the application of ECT test on the engineering projects to address the issues of soft foundation in the off-shore area,such as insufficient bearing capacity and inadequate anchoring capacity of the pre-stressed anchors.The ECT was utilized to improve the behaviors of soft soils in Dalian City,increase the anchoring force of the pile anchor system used in the deep foundation,and verify the feasibility of the ECT for the pile anchor system.It is the first application of the ECT on the deep foundation.The results of this research provide references and suggestions for the future engineering projects.