Experimental Study on Reinforcement of Mucky Clay by Electroosmosis-Calcium Chlorideunder Intermittent Current

[Objective] This study aims to improve the reinforcement effect of electroosmosis and enhance its engineering practicability by applying an intermittent current to the electroosmosis-calcium chloride method. [Methods] Laboratory model tests were conducted on mucky clay reinforced by the electroosmosis-calcium chloride method under different intermittent current ratios, in order to reduce energy consumption and electrode corrosion, as the on/off time ratio is a key factor influencing reinforcement effectiveness. The effects of different on/off ratios on the reinforcement of mucky clay were analyzed, and the underlying reinforcement mechanisms were investigated. The off-time was fixed at 1 h, while the on-time was set at 8 h, 5 h, and 2 h. The concentration of the CaCl2 solution was 10%. [Results] The addition of CaCl2 increased the electrical conductivity of the soil, which enhanced the electroosmotic drainage by about 49.3%. At the same time, cementitious substances were generated at the cathode and the average shear strength of soil was enhanced by about 240%, which dramatically improved the strengthening effect of electroosmosis. Meanwhile, the anode corrosion and energy consumption increased by 6.6% and 12.0%, respectively, after adding CaCl2. Applying intermittent current could reduce the anode corrosion and energy consumption induced by the addition of CaCl2, but it also weakened the electrochemical reinforcement effect, which was related to the on/off duration. When the on-time was 2 h, part of the Ca2+ could not migrate to the cathode, the amount of cementitious products decreased, and water molecules at the cathode flowed back under the hydraulic gradient, resulting in a reduction in the electrochemical reinforcement effect. When the on-time was 8 h, the electrolysis at the anode and cathode produced more H+ and OH-, which aggravated the dissolution and oxygen-evolution corrosion of the anode. Meanwhile, the generated metal oxides/hydroxides increased the surface film resistance of the electrode, leading to more heat production in the soil and unnecessary energy consumption. In addition, prolonged current caused gas accumulation at the cathode, resulting in detachment between the electrode plate and soil, an increase in interfacial resistance, and further increase in energy consumption. By comparison, the on/off time of 5 h/1 h showed the best reinforcement effect, which increased the drainage volume by 55.7% and increased the shear strength of cathodic soil by about 400%. The energy consumption per unit drainage decreased by 6.7%, and anode corrosion decreased by 4.7% compared with continuous current. [Conclusions] The electroosmosis-calcium chloride method under intermittent current can mitigate the drawbacks of conventional electroosmosis, namely limited strength improvement, severe electrode corrosion, and high energy consumption. It therefore provides an optimized approach for its practical engineering application.