Effect of Fines Content in Silt-Sand Mixtures with Different Saturations on Microbial-Induced Calcium Carbonate Precipitation

In general, soil in its natural state is not geotechnically suitable to achieve the intended engineering objectives. Therefore, refining them to improve their mechanical properties is essential. In recent years, soil improvement based on microbial-induced calcium carbonate precipitation has been proposed as a new branch in geotechnical engineering, also referred to as the green method. In this method, via nonpathogenic microorganisms capable of producing urease enzyme, a calcium carbonate precipitate bond is formed by the carbonate ion and its bond with the calcium ion. This causes the soil particles to adhere. In this study, using Sporosarcina pasteurii with high urea enzyme activity and a suitable cementation solution, the formation of calcium carbonate precipitate in three types of sand with different percentages of silt and with different degrees of saturation was investigated, and a uniaxial compressive strength test was conducted. The results indicated that the highest compressive strength was obtained with a 10% increase in the fines content with a degree of saturation of 20%. Moreover, as the fine content and degree of saturation increased, the compressive strength decreased despite forming a high percentage of calcium carbonate precipitate. The results also presented here indicate that the effect of MICP on silty sands depends on degree saturation, fine content and the fabric governing the soil structure. The findings also demonstrated that in low fines content, calcium carbonate bio-deposition could be utilized to improve soil parameters owing to their economical nature.