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Microbially induced calcium carbonate-based cementation of fractured sandstone
Alahmar, Maryam
Alahmar, Maryam
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2024
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2026-04-09
Abstract
Microbially induced calcium carbonate precipitation (MICP) is an emerging ground improvement technology that has the potential to meet the growing demand for grout due to increasing construction activities and to reduce the negative impact of these activities on the environment. However, some of the challenges of this technique include the heterogeneous distribution of the precipitated calcium carbonate and clogging near the injection source, especially due to the difficulties associated with monitoring subsurface bio-treatment.
The stability and success of underground projects require an understanding of the mechanical behavior of the grouted fractures, as defects in the grout impact the stability of underground projects and may cause mechanical failure of the grouted rock system. Deficiencies in the grouted rock system may also affect the hydraulic properties of the grouted rock by allowing water to ingress. Therefore, understanding the mechanical and hydraulic behavior of bio-grouted fractured rock is crucial for assessing the potential of MICP as a ground improvement in underground engineering applications.
This Ph.D. dissertation describes an extensive experimental program that synthesized different strategies of injecting microorganisms into fractured rock; investigated the effect of different inoculation and incubation conditions on grouting prefabricated fractures; and monitored the bio-cementation process and evaluated the bio-cementation distribution at the pore scale spatiotemporally and non-destructively using nuclear magnetic resonance (NMR). The experimental program also included digital imaging correlation (DIC) technique and computed tomography (μ-CT) imaging to (1) elucidate the failure mechanism of the bio-grouted system under different loading conditions, considering the anisotropic influence of the grouted fracture orientation, and (2) investigate the effects of the bio-grout content on the mechanical and hydraulic properties of the grouted system.
A substantial improvement in anti-seepage of fractured rock was achieved due to the homogeneous distribution of calcium carbonate precipitation along the fracture rather than clogging near the injection source. Furthermore, the results revealed that the bio-grout can transfer both tensile and shear stresses while maintaining a strong interfacial bond with the original rock. However, some fracture orientations may not be favorable for the MICP-based grout. Since the reinforcement effect of the bio-grout can be enhanced by increasing the CaCO3 concentration, using a high CaCO3 concentration or using a combination of multiple ground improvement methods may be necessary to reinforce fractures with varied orientation and to ensure the stability of the underground structure. NMR was proven as a non-invasive method that can detect calcium carbonate precipitation, and therefore, has the potential to monitor the MICP process in situ. This study demonstrates some of the possibilities and limitations of MICP-based grout to advance the sustainability of underground engineering.
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