This study investigates the effect of the electrokinetic process, which includes electromigration and electro-osmosis, and the cause of process termination. The results show that electromigration strongly contributes to the ionic transportation in the first 10 days, and electro-osmosis is the dominant mechanism during 11-40 d. A total of 90% of Na+ was transported out of the compact soil, whereas Ca2+ was mainly retained near the cathode in the form of precipitation. The soil colloid electric double layer (EDL) was compressed at the anode because of the high concentration of free Ca2+ in the first 10 days and became thinner after 40 days because of the pH reduction. At the cathode, the EDL was first enlarged with the increase in pH and subsequently compressed because of the Ca precipitation film. Correspondingly, partial soil particles that were smaller than 712 nm were aggregated into larger ones because of the compression of EDL, particularly at the anode. In addition, partial soil particles were transported with EOF toward the cathode, which increased the percentage of colloid particles (<2 mu m). The decrease in the number of mobile ions and the aggregation of soil colloid particles are the main reasons for the termination of the electrokinetic process. Therefore, appropriate electrolytes to condition the soil colloid properties in different phases and soil sections can be used to maintain the EK remediation. (c) 2017 Elsevier Ltd. All rights reserved.