Effects of push-pull injection-suction spacing on sand biocementation treatment

The process of ureolysis-driven biocementation is used to improve granular soils. The precipitation of calcium carbonate (CaCO3) crystals results from the reactions of urease generated by ureolytic bacteria and chemical reagents, which strengthen or bind soil particles together. Using a lab-based scaled physical model, this paper investigated the influence of selected spacing intervals (107 mm, 214 mm and 321 mm) on the effectiveness of biocementation via the injection-suction or 'push-pull' approach. Polystyrene moulds were used to create soil specimens. It was then injected with 6 cycles of the treatment solutions at the intervals stated. The compressive strengths and CaCO3 content of the biocemented soil specimens were measured after curing, as well as scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared (FTIR) spectroscopy, and effluent analysis (pH and ammonium measurements). The biocemented soil specimens with different spacing intervals obtained compressive strengths of 2.53 +/- 1.06 to 4.2 +/- 2.3 MPa, while the CaCO3 contents were from 2.78 +/- 0.3 to 11.16 +/- 1.5%, respectively. The elemental compositions and bonding of CaCO3 precipitates in the biocemented soil were confirmed by EDS and FTIR spectra, while SEM micrographs revealed chip-like and irregular rhombohedral crystal forms. The results demonstrated that injection spacing had an effect on MICP-treated biocemented soil.