Soil Improvement by Electrokinetic Sodium Silicate Injection into a Sand Formation Containing Fine Grains

The effect of electrokinetic sodium silicate injection into sand formation containing fine grains was studied in this research. A soil was grouted by Na-silicate in a 160 mm length electrokinetic cell with a 1 V/cm potential gradient for 1 week. Silicate solutions of 5% and 10% concentrations were injected through the reservoir next to the anode electrode, while 10% phosphoric acid or 30 mg/l bicarbonate solutions were used in the cathode chamber. When comparing the results, it was evident that the electrokinetic (EK) process without additives does not significantly enhance soil strength, except in the vicinity of the cathode electrode. Specifically, the most notable increase in strength was observed in the section proximal to the cathode, which demonstrated approximately 3.1 times higher strength than the control sample (i.e., without EK application). The obtained results indicate that injecting 5% and 10% Na-silicate solutions significantly increase the strength of soil all over the sample. Significant improvement in soil strength was observed when Na-Si was injected with bicarbonate as a catholyte during the EK process. Strength at the anode increased by 82% and 107% at 5% and 10% Na-Si concentrations, respectively. Resistance in the middle of the cell samples remained consistent for both concentrations. Immediate application of bicarbonate catholyte and silicate injection notably enhanced soil strength, while efficiency decreased when Na-Si was injected with phosphoric acid catholyte, especially near the cathode. Higher silicate concentrations resulted in reduced penetration length in both acid and bicarbonate catholytes. It can also be concluded that adding silicate to the anode chamber meaningfully reduces the electro-osmotic flow after 2 or 3 days.