Study the grain size and infiltration method effects for sand soil improvement using the microbial method

Today, with regard to land shortage and ever-increasing growth of the world's population, construction on loose soil has been inevitable. Therefore, to deal with this issue, it is necessary to improve project site materials. The conventional soil improvement techniques are limited due to high costs and environment unfriendliness. In this regard, microbial-induced calcite precipitation (MICP) is a relatively environment-friendly method that is efficient for soil improvement. In this method, hydrolysis of urea by bacteria containing urease enzyme and in the presence of soluble calcium ions leads to the precipitation and attachment of CaCO3 among the soil grains. In this study, the effects of grain size, a method of infiltration, infiltrated bacteria suspension (BS) volume and infiltrated fixation solution (FS), and cement solution (CS) on Quartz sand shear strength are investigated. The results of the conducted tests showed that among four different infiltration methods, continuous infiltration of BS and CS, have the strongest effect on shear strength. Studying shear strength two different sand sizes based on direct shear test showed that sand with larger effective size and higher permeability has a shear strength 6.2 times compared to non-treated sand. The results showed that soils with less volume of infiltrated bacteria have a higher shear strength. Adding a FS to three different BS volumes showed the one with the lowest amount has the highest shear strength. According to the X-ray diffraction and scanning electron microscopy analyses, the efficient CaCO3 precipitation between the soil particles is confirmed.