Ground improvement with single treatment using Mg 2+ modified all-in-one MICP solution: 1m sand column

The potential of microbially induced carbonate precipitation (MICP) for soil bio-improvement has been widely studied as an alternative to traditional cementation by Portland cement. While multiple-phase injection techniques are commonly used for MICP treatment, they impose complexities and require a high number of injections. One of the latest developments in the biocementation research area is using the one-phase-low-pH MICP method as a more effective and efficient alternative to the traditional two-phase method. The published studies in one-phase MICP used 1M concentration and injected all-in-one solution several times. So, this study primarily investigated the possibility of soil improvement by a single injection of high-concentration all-in-one solution in 1m columns. This high concentration can impose a toxic effect on bacterial activity and hinder urea conversion. Also, a high concentration of salts such as calcium or magnesium chloride can increase the ionic strength and decrease the uniformity of carbonate precipitation. The effect of 20% magnesium substitution and decreasing the initial temperature of substances were studied. The experiments in aquatic steps demonstrated that these magnesium cations and low temperatures can prolong the lag phase. The collected precipitation from magnesium-included solutions showed an enhancement in the crystal structure of calcium carbonate formations. The transportability of all-in-one solutions was examined by injection of 6 pore volume solution through a 20 cm sand column and comparing the optical density of effluent to the influent. Solutions with magnesium contents and low temperature demonstrated a higher transportability. Eventually, 1 m sand columns were treated with all-in-one solution and the most homogeneous urea conversion and calcium carbonate precipitation were observed in the column injected with a low temperature of magnesium substituted solution.