Investigating the Shear Strength of Biologically Improved Soil Using Two Types of Bacteria

Many types of researches have been carried out on sandy soils to improve the fertility through bacteria. In this regard, after measuring the activity of urease enzymes in urea bacterial sediments, calcium carbonate was applied in Sirjan soil (southeast of Iran), and the native bacteria of this soil were isolated. The strains of these microorganisms, because of the Come and aridity in the region and the severity of the environmental conditions in the area, have a greater resistance to chemical and physical factors and are compatible with the environment of this region. In this study, we tried to use two types of soil bacteria: one is Sporosaercina pasturii, many researchers have been working on this bacterium and the effects of soil improvement, and another is the native bacterium found in Sirjan soil (Acinetobacter calcoaceticus strain Nima). Thirty samples were taken in the same conditions and experiments to evaluate the use of native bacteria of Sirjan in soil remediation by direct shear testing, seismic electronic microscopy, and microscopic scanning (SEM) were performed on the samples. The treatment period for this study was 28?days. The results showed that the angle of internal friction increased for the treated A. calcoaceticus Nima (42%) and S. paturii (39%) compared to untreated samples. Also, adhesion between particles increased by 14.5 times for A. calcoaceticus Nima and 13.5 times for S. paturii. Finally, shear strength for soil treatment increased by4.6 times for A. calcoaceticus Nima and 3.9 times for S. pasturii. The use of indigenous strains in the natural environment due to the adaptation of strains to environmental conditions can increase the production of bio-cementation. It is, therefore, possible to use native bacteria for biologically improved soil as an appropriate alternative rather than traditional methods due to environmental problems.