Development of an Improved Immersing Method to Enhance Microbial Induced Calcite Precipitation Treated Sandy Soil through Multiple Treatments in Low Cementation Media Concentration

Experimental immersing method is one of treatment methods to study the microbial induced calcium carbonate precipitation (MICP) that can improve engineering properties of sandy soil. Cementation media concentration and treatment frequency are two factors that can influence the effect and efficiency of MICP process in the immersing method. An improved immersing treatment method is developed in this study to enhance MICP through multiple treatments with low cementation media concentration. Experimental results show that repeated treatments under cementation media concentration of 0.25 M Ca, 0.5 M Ca, and 0.75 M Ca can improve the utilization of cementation media and increase the unconfined compression strength of MICP-treated specimens up to 6400 kPa. Meanwhile, the hydraulic conductivity of MICP-treated sand reduced from untreated of 0.14 cm/s to 0.001 cm/s after four MICP treatments. Dry density of MICP-treated sand increased with higher concentration of cementation media and more treatment times. At the cementation media concentration of 0.25 M Ca, the MICP process can be repeated up to 4 times with an efficient improvement of mechanical strength. When the cementation media concentration increased to 0.5 M Ca or 0.75 M Ca, the optimum MICP treatment times reduced to two due to the reduction of void ratio.