The comparison of the performance of biological improvement in sandy soils by the injection and the flow-through methods

Bio-improvement has been identified as an environmentally friendly method, Microbially Induced Calcium Carbonate Precipitation (MICP) is the predominant technique in this domain. The four main methods introduced for MICP are the injection, surface injection or flow-through, immersion, and mixed methods. Among these, the injection and the flow-through methods hold particular significance. In this study, the efficiency and performance of these two methods were investigated in soils with different relative densities and varying volumes of bacterial suspension injection.To assess the efficacy of these methods, various tests including optical density, urease activity, permeability, uniaxial strength, calcium carbonate pericipitation percentage were conducted. The flow-through method, with its easier implementation, absence of the need for special equipment, minimal reduction in permeability, more uniform dispersion of the resulting cement, and the ability to achieve comparable strength to the injection method when using an injection volume equal to the pore volume in high relative density, stands out as the more suitable and economical approach for improving sandy soils. Despite its cost-effective implementation, the flow-through method necessitates more injection cycles, particularly in the injection volume of two-thirds and one-third of the pore volume, to achieve the same strength as the injection method. This aspect diminishes the economic difference between improvement using the injection method and the flow-through method in laboratory. This aspect diminishes the economic difference between improvement using the injection method and the flow-through method in a laboratory conditions.