SOIL IMPROVEMENT BY MICROBIAL INDUCED CALCITE PRECIPITATION AND A CHEMICAL METHOD FOR LIQUEFACTION MITIGATION

Microbial induced calcite precipitation (MICP) is a geochemical process for ground improvement by enhancing the mechanical properties of the soil stratum. A bacteria and nutrient containing liquid are injected into the sand to precipitate the formation of calcium carbonate crystals through the metabolism of microorganisms. The calcium carbonate crystals precipitate in pores between the grains of sand, effectively cementing the particles of sand together and filling the pore volume, consequently, increasing the shear strength and reducing the permeability. However, the functioning of the MICP method is quite sensitive to environmental conditions such as temperature and humidity. Another way to cement the soil layers is to use a chemical process where a Na₂CO₃-CaCl₂ liquid mixture is added to produce CaCO₃ which helps to harden the soil. However, this method has significant undesirable side effects in the ground environment. In this study, a series of experiments is carried out comparing samples that have been improved by MICP and a chemical method under different conditions with the original non-improved samples. The experiments include direct shear testing, constant head testing and centrifuge testing. The results show that the treated sand layer has better resistance to liquefaction, decreased excess pore water pressure, and improved settlement which also shortens the excess pore water pressure dissipation time. In addition, it is also demonstrated that the temperature, humidity and nutritional liquid have a critical effect on the effectiveness of the MICP and chemical methods.