Numerical investigation of microbially induced calcite precipitation and its influence on the permeability of soil

Microbially Induced Calcite Precipitation (MICP), a bio-mediated cementation process that improves the geotechnical properties of soils through the precipitation of calcium carbonate, is becoming a promising alternative to traditional soil improvement methods. This technology in recent years has been used in the production of building materials, construction of waterproof barriers, biofilm to prevent water leaks or pollutant leaks from storage. Other geotechnical applications currently being explored include cementation of sands to enhance bearing capacity and liquefaction resistance, soil erosion control and remediation of soil and groundwater impacted by metals and radionuclides. Challenges in bio-mediated ground modification include upscaling processes from the laboratory to the field, in situ monitoring of reactions, reaction products and properties, developing integrated biogeochemical and geotechnical models, management of treatment by-products, establishing the durability and longevity/reversibility of the process. MICP has been shown to increase soil stiffness, reduce permeability and increase shear strength in laboratory experiments. The current study presents the numerical model for microbially induced calcite precipitation predicting the reduction of permeability over time due to biomineralization in the fracture of rocks and prevention of leakage from C°₂ storage reservoirs. The results show the permeability of the fracture-layer can decrease by one order of magnitude in a radius of 3 meters and by the factor of 3 in a radius of 5 meters from injection position. The maximum reduction of permeability was nearly by two orders of magnitude from the initial value. Identification of different process limitations, such as bacterial activity and reaction rates, enables the control of MICP for its use in geotech-nical engineering. The primary challenges in this area include assessment of subsurface ecosystems and their interaction with the available fluids and minerals, mapping and modelling of subsurface variability of pore structure, mineralogy, ground water flow and transport and bacterial diversity. Techniques for real-time monitoring require improvement. Upscaling requires extensive experimental work that is hypothesis-driven owing to the inherent complexity of natural systems. The experimental work must be complemented by rigorous analytical and numerical modelling to identify the first-order principles controlling the system. Interdisciplinary research requires greater interaction between scientists and engineers, formation of interdisciplinary work groups and departments.

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