Influence of degree of compaction on electrokinetic remediation of unsaturated soil

In order to evaluate the electrokinetic process for unsaturated soil with different compacted conditions, six remolded soil samples containing the same water content (16 wt%) were compressed to obtain the various degrees of compaction (96.87% to 103.37%). All the lab-scale experiments were performed by applying a constant electrical voltage (1 V/cm). The electrical parameters related to the electrokinetic process were monitored to evaluate the influence of the soil degree of compaction on this process. The obtained results indicate that the soil compaction degree could influence the electrical current, the migration velocity of the voltage front, and the controlling mechanism of water transport during the electrokinetic processes. Followed by the initial decline, the electrical current of soil with a lower degree of compaction (96.87%) would increase at 0.7 mA/h, which was about seven times larger than that of the soil with a higher degree of compaction (103.37%). The migration velocity of voltage front in the soils increased with decreasing compaction degree. The voltage front migrated from the cathode towards the anode at 6.66 mm/h in the soil with a lower degree of compaction (96.87%). In comparison, the migration velocity decreased to 1.75 mm/h in the soil with a higher degree of compaction (103.37%). Both hydraulic and electrokinetic driving forces could influence the water transport in unsaturated soil. The results demonstrate that the catholyte entering the soil under the hydraulic gradient could be opposite to electro-osmosis. The electrokinetic driving force would be a major controlling mechanism for the unsaturated soil with a higher degree of compaction. For the soil with a lower degree of compaction, the hydraulic driving force would affect the water transport in the soil during its initial saturation period. Moreover, with the increase in soil saturation, the effects of hydraulic driving force were weakened, and the electrochemical properties of the pore solution appeared to be the dominant factor for the electrokinetic process.