Effects of MICP Stabilization Using Aerobic Denitrification and Non-Sterile Ureolysis Pathways on Sand Column Properties

Document Type

Conference Proceeding

Publication Date

1-1-2026

Abstract

This study explores the effect of microbially induced calcite precipitation (MICP) on the geotechnical properties of sand columns, utilizing two distinct microbial treatments: ureolysis and aerobic denitrification. Typically, sterile conditions are used for cultivating ureolytic bacteria, and only a specific strain is used for MICP applications. Both using a single strain and the sterile conditions pose challenges and increase the cost of the soil treatment when upscaling to field and real-world applications. This study employed a non-sterile approach for cultivating a ureolytic bacterial community in order to address these challenges. Ureolysis also produces ammonia as a byproduct, which can lead to environmental concerns in certain applications, e.g., stabilization projects close to bodies of water. While denitrification offers an alternative without ammonia byproducts, it typically requires strict anaerobic conditions, limiting its practical application, especially at shallow depths. In this study, a series of sand column experiments was conducted using both non-sterile ureolysis and aerobic denitrification pathways. The aerobic denitrification pathway’s ability to function effectively under varying oxygen accessibility was evaluated. Samples were prepared under two conditions. Fully saturated specimens restricted oxygen diffusion, while open-cap specimens were exposed to air and thus more aerobic. These conditions were used to examine how oxygen availability affected soil strength and calcite precipitation. In addition, the effect of injection direction was investigated for each saturation condition and treatment pathway. Microorganisms from activated sludge were cultivated separately for each pathway. Strength improvements were assessed through laboratory Cone Penetration Testing (CPT), and the impact of MICP on hydraulic conductivity was investigated through permeability measurements after each treatment cycle. Scanning Electron Microscopy (SEM) confirmed the precipitation of calcium carbonate, while calcite content analysis provided insights into its distribution within the sand column. The viability of MICP treatment via the denitrification pathway under aerobic conditions was confirmed. The results demonstrated that the 9-cycle aerobic denitrification treatment achieved higher strength compared to the 2-cycle ureolysis treatment. Finally, the combined effect of injection direction and saturation conditions on calcite precipitation and soil strength is discussed.

Publication Title

Geo Congress 2026 Geosynthetics Pavements and Soil Improvement Selected Papers from Geo Congress 2026

ISBN

[9780784486764]

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