Effect of Bacterial Strain on MICP and its Application for the Erosion Control of Fine Sands
Tangential flow-induced erosion poses a major threat to a wide variety of engineering structures, including earth-filled embankment dams and oil and gas extraction wells. Current mitigation solutions are limited to mechanical approaches (e.g. filters, gravel packs), relying on the fulfilment of a ‘p...
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| Format: | Thesis |
| Language: | unknown |
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Apollo - University of Cambridge Repository
2020
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| Online Access: | https://dx.doi.org/10.17863/cam.55396 https://www.repository.cam.ac.uk/handle/1810/308305 |
| Summary: | Tangential flow-induced erosion poses a major threat to a wide variety of engineering structures, including earth-filled embankment dams and oil and gas extraction wells. Current mitigation solutions are limited to mechanical approaches (e.g. filters, gravel packs), relying on the fulfilment of a ‘paradoxical permeability-retention criterion’; and to the use of emergency hydraulic head reduction which limits serviceability. In this context, microbial induced calcium carbonate (CaCO3) precipitation (MICP) could be used to enhance the erosion performance of soils. This research investigates the influence of the CaCO3 microstructure on the macromechanical erosion response of fine sands by combining instrumental techniques for characterisation, with element-scale flume testing and controlled modelling of a heterogeneous layered system. The flume tests employed a newly designed Erosion Function Apparatus (EFA) and testing procedure to measure surface erosion, focusing on fine-coarse sand interfaces treated with the same soil bacterium (Sporosarcina pasteurii), but varying urea-CaCl2 solution concentrations. The key aspect examined was the role of CaCO3 micro-architecture – comprised of the CaCO3 vertical profile, crystal size and distribution, and morphology. Results showed that higher CaCO3contents, bigger crystals, and cohesive bonds yield lower erodibility values. It was also seen that crystal growth mechanisms could change depending on bacterial distributions, urea-CaCl2 solution concentrations, and the pore space of the original granular material. As MICP moves from research into practice, the effect of bacterial strain on CaCO3 precipitation also needs to be considered. The morphology, mineralogy and crystalline properties of biominerals precipitated by three different ureolytic microorganisms were henceforth investigated. These strains were: S. pasteurii, S. aquimarina, and S. newyorkensis – a newly isolated microbe from the Daini-Atsumi Knoll in offshore Japan. From in vitro experiments it was found that CaCO3 polymorph selection can be controlled through selection of ureolytic strain with appropriate precipitation kinetics, and that metastable polymorph stabilisation is dependent on the kinetics of the mobile water contained within the crystal structure. Finally, the Cambridge Plane-Strain Sand Production Apparatus (SPA), through the incorporation of Particle Image Velocimetry, was used to examine the effect of bacterial strain-specific MICP on the deformation mechanisms of a layered granular system resulting from lateral unloading due to erosion. It was observed that MICP treatment reduces sand production at the expense of ductility, however, this behaviour becomes more prominent with increasing CaCO3 polymorph stability – namely, amorphous calcium carbonate (ACC), vaterite, and calcite. Correlations between microstructual characterisation, and EFA and SPA results highlighted the potential for designing bio-reinforced geo-materials that capitalise on the different CaCO3 microstructural features. : The author would like to acknowledge the EPSRC Centre for Doctoral Training in Future Infrastructure and Built Environment at the University of Cambridge (EPSRC grant reference number EP/L016095/1). In addition, this study was conducted as part of the activity of the Research Consortium for Methane Hydrate Resources in Japan [MH21 Research Consortium] as planned by the Ministry of Economy, Trade, and Industry (METI), Japan. Thank you to the crew of D/V Chikyu for the 2012 JOGMEC/JAPEX pressure coring operation. In addition, the author would like to acknowledge the additional financial support from the Cambridge Philosophical Society Research Studentship. |
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