Biological improvement of sandy soil by microbial induced carbonate precipitation and the affecting factors

Microbial-induced calcite precipitation (MICP) is a relatively green and sustainable soil improvement technique. It refers to a chemical reaction network that is managed and controlled within soil through biological activity and whose byproducts alter the engineering properties of soil.To treat soil, first, the microbial population in-situ is augmented by the injection of additional urease positive bacteria and then reagents are added. This paper provides an overview of the factors affecting the MICP in soil. Several factors including nutrients, bacteria type, geometric compatibility of bacteria, bacteria cell concentration, fixation and distribution of bacteria in soil, temperature, reagents concentration, pH, and injection method are introduced. These factors were found to be essential for promoting successful MICP soil treatment. Furthermore, a preliminary laboratory test was carried out to investigate the potential application of the technique in improving the strength and impermeability of a sand specimen and utilized techniques, materials, methods and empirical process during the test are explained. The results showed that as a result of the calcite precipitation, shear wave velocity increased up to 1000m/s and UCS strength increased to about 300Kpa and permeability of soil decreased significantly upon MICP treatment.