Investigation of simultaneous effect of the remaining time, molarity and bacterial solution concentration on shear strength of sandy soils stabilized by bio-cementation method

Soil bio-remediation is one of the developing methods of soil improvement and the reduction of environmental problems due to the injection of chemicals in the soil is one of the superior features of this method compared to other common methods. It was created by linking the fields of civil engineering, geochemistry, and microbiology. The basis of soil improvement by biological cementation method is based on the microbial production of calcium carbonate precipitation, which is inspired by the formation of sandstone in nature and with the help of bacteria that have precipitation and hydrolysis of urea to enhance the technical specifications of soil. The steps of soil remediation in this method are that in the presence of Bacillus Pasteurii bacteria, crystals are formed which are the result of urea reaction and a source of calcium, which is usually calcium chloride. These crystals are placed in empty spaces of the soil and represent the reason why the adhesion of soil particles increases significantly and its strength increases. In order to manage the consumption of materials used, it is better to obtain optimal values during studies. For this purpose, in this study, the cemented samples were subjected to triaxial tests, permeability, and SEM testing. In consolidated undrained triaxial experiments, the trend of soil resistance over time was investigated by considering different retention times and different molarities. The optimal amount of molarity of the materials used and the concentration of bacteria and the optimal retention time were obtained according to the results of experiments performed in this method. Also, by examining the resistance of cemented samples, an increase in strength in the range of compared to clean sand was observed. Examination of the time parameter pointed to the formation of calcium carbonate precipitation and their final setting up to days. After days, the trend of increasing soil resistance exhibited a constant amount.