Application of electric fields to improve cementation homogeneity of biogrouted sands

Abstract

AbstractThe inhomogeneity of cementation is a common problem in soil improvement with microbially induced carbonate precipitation process (MICP), which is caused by uneven spatial distribution of bio‐induced calcium carbonate precipitation. Electric field adjustment method was developed and adopted for improving cementation homogeneity of bio‐grouted sands in this research. Horizontal one‐dimensional biogrouting experiments were conducted in sand columns under 0.1 V/cm of direct current (DC) electric field. The column treated with DC electric field showed a significant improvement in homogeneity of calcium carbonate precipitation as compared to the control (without DC electric field). Spatial distribution of calcium carbonate in columns were affected by the properties of bacteria, whether suspended or attached. In general, the attached bacteria with uneven spatial distribution played an important role in the calcium carbonate precipitation when flow rate was regulated at 0.54 cm/min, while the suspended bacteria could also be attached upon times with consumption of cations during biogrouting. With the influence of electric field, suspended bacterial transport in porous media occurred in one direction to the target locations because of the electrophoresis at an average speed of 0.14 cm/h, while sodium ion was found to be moved from anode to cathode by electromigration approach. Electrolysis of water, on the other hand, resulted a slight fluctuation in pH, even though this variation did not show any significant effect on the metabolic activity of bacteria and microbial‐induced carbonate precipitation process. The redistribution of suspended bacteria and sodium ion in porous media provided a possible for attached bacteria to distribute uniformly, which could be considered as the key factor to influence spatial distribution of the bio‐induced calcium carbonate in application of electric field adjustment method.