Sustainable solidification of high water content marine deposits (MD) is crucial for coastal infrastructure, where clay content (CC) of MD critically affects its performance. This study proposed an in-situ treatment of magnesia-based bio-cement (MBC) for MD solidification. This novel approach utilizes concentrated bacteria solution to hydrolyze urea directly within high water content MD and then engage the bio-carbonation of reactive MgO. The in-situ MBC-solidified MD (MBC-samples) with 10-70% CC were prepared to validate the feasibility and reveal CC effects by investigating their mechanical properties, chemical characteristics, and microstructures. The results indicate that in-situ MBC can effectively solidify high water content MD by utilizing its inherent water for urea hydrolysis, circumventing further water content increment by bacteria solution addition. The increase in CC significantly improved unconfined compressive strength (UCS) by 370.0% to 0.94 MPa, but decreased the degree of carbonation (DC, evaluating hydrated magnesia carbonates (HMCs) yield) by 30.3% to 0.31. Pre-hydrolysis treatment increased the DC and UCS of MBC-samples by 24.4% and 177.0%, respectively. Although higher CC inhibits urea hydrolysis within MD and reduces HMCs production, it decreases pore volume and dominant pore size, changing HMCs development and distribution, which compensates for the lower DC and ultimately improves the UCS of MBC-samples. The relationship between CC and UCS was quantitatively analyzed by considering the decreased DC effects via inhibiting reactions and microstructural refinement through reduced dominant pore diameters with higher CC. These findings provide theoretical and practical insights for sustainable marine deposit solidification.

High water content marine deposits,Clay content effects,Soil solidification,Magnesia-based bio-cement,In-situ treatment