Bio-İmprovement of Dune Sand by Bacterial Medium Cultures using Sporosarcina Urea and Bacillus Subtilis

Abstract

Sand storms are catastrophic geological challenges worldwide in arid and semiarid areas with growing intensity. Engineering geologists and geotechnical engineers are always trying to monitor the desertification phenomenon and stabilize weak soils with dust storms origin through environmentally friendly procedures. It is assumed that erosion resistance can be improved by improving the strength of soils. In the past few years, microbial-induced calcite precipitation (MICP) has been utilized as a sustainable ground improvement technique. In this method, urea is fractured by bacterial urease enzymes, and the biochemical reaction network is then completed by adding cementation solution and instigating calcite precipitation which improves the mechanical and physical properties of the soil. In the presented research, a single culture of Sporosarcina urea (S. urea) and a mixed culture of Sporosarcina urea and Bacillus subtilis (S. urea + B. subtilis) mediums were used for the bio-cementation of typical dune sand. Firstly, the medium culture was gravitationally injected into the soil specimens in one cycle. Secondly, the cementation reagent (urea + calcium chloride) was injected into the specimens in two cycles. After a specific curing period, the specimens were evaluated using unconfined compression strength (UCS), permeability, direct shear, and California bearing ratio (CBR) tests. The tests outcomes revealed a considerable enhancement in strength and stiffness and a significant reduction in permeability for all treated soil specimens. Finally, the improvement of stabilized specimens was verified by quantifying calcite content, scanning electron microscopy (SEM) images, and X-ray diffraction (XRD) analyses on selected treated specimens.