The Characterisation of Carbonate-Bearing Soil Ahead of Future Biomineralisation Treatments

The C2C project, a Research Centre to Centre collaboration began in 2020. It involves an international team of scientists and engineers from three research centres: the Centre for Bio-mediated and Bio-inspired Geotechnics (CBBG), Arizona State University USA; the Energy Efficient Materials Research Centre (EEM) at Queen’s University Belfast, Northern Ireland; and the Irish Centre for Research in Applied Geoscience (iCRAG), Ireland. The C2C project’s objective is to conduct a multi-scale investigation into bio-based mineral precipitation using carbonate bearing granular soils and construction related waste. Bio-based mineral precipitation is a potential green energy solution to the remediation of problematic soils. It has been gaining in popularity over the past two decades and involves expediting the naturally occurring process of calcite precipitation in granular soils. Through this process calcite bonds are formed between soil grains. As a result, engineering characteristics of the soil are improved. The permeability is reduced while the shear strength, stiffness and dilatancy of a soil are increased. Research in bio-based mineral precipitation requires a multidisciplinary approach. This study involves the characterisation of a carbonate bearing glacially deposited soil ahead of biomineralisation trials. An understanding for the soils properties is important in terms of predicting the soils suitability and likely reaction to biomineralisation treatments. The soil selected is from Blessington, Ireland. It represents an unlithified Quaternary soil, common to the Earth’s northern hemisphere. Biogeochemical reaction pathways and reaction kinetics for carbonate bearing soils are expected to be more complex than those previously studied by CBBG in pure silica soils. The analyses reported here aim to characterise the Blessington soil in order to achieve a macro to micro scale perspective on the soil’s geotechnical parameters. The site investigations carried out detail the in-situ parameters of the soil and its groundwater. Aspects of field parameters recorded include the soil’s structure, stress state, strength and stiffness, as well as resistivity and groundwater geochemistry. Geological observations lend context to the soils field conditions. Field results are complemented with laboratory studies aimed at classifying the soil further and obtaining the soils physical and particle characteristics. Studies to establish the engineering properties of the soil such as permeability and compressibility are presented along with studies of the soils small-strain mechanical behaviour at varied consolidation stress. Micro-scale studies include the mineralogy, microtopography and bacterial assemblage of the soil are also reported. Results detailed here are intended to provide baseline datasets that can be used to inform future treatment designs ahead of column, tank and field scale testing.