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Improving deformation characteristics of sand soils using bio-improvement methods

Tunalı, Mert
Utilizing biological processes is new and innovative method which can be used to improve engineering properties of soils in an environmentally friendly way. In this study, a recently introduced bio-improvement method named microbially induced calcite precipitation (MICP) is used to improve the strength and deformation characteristics of soft soils. For that purpose, ureolytic bacteria were utilized to improve the strength properties of soils. Ureolytic bacteria can induce enzymatic hydrolysis of urea, which results in production of free ammonium (NH4+) and bicarbonate (HCO3-) ions. In case of existence of free calcium (Ca2+) ions in the environment, calcite (CaCO3) precipitation may occur as the result of a reaction between HCO3- and Ca2+ ions. This reaction results in cementation of soil grains, which results in the improvement of engineering properties of soil. Within the scope of the study, both MICP’s applicability and its effect on strength properties of soil were investigated by performing direct shear tests. More specifically, improvement efficiencies of Sporosarcina pasteurii (ATCC 11859), a widely studied bacterium, and Bacillus licheniformis (ATCC 14580), a relatively new introduced bacterium, were examined with samples prepared at different relative densities and with different number of injections. The improvement in the strength values are also supported with the help of sophisticated imaging tools such as Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) techniques.