Numerical Investigation on the Microbial Shallow Grouting Reinforcement in Permeability Anisotropic Seabeds and Liquefaction Evaluation

Microbially induced calcium carbonate precipitation (MICP) offers a sustainable approach to reinforcing marine soils, with broad potential in coastal protection, infrastructure reinforcement, and landing of autonomous underwater vehicle (AUV), where stable seabed is critical. This study presents a multifield coupled numerical model that considers bacterial growth, chemical reactions, fluid flow, solute transport, and wave actions. The model is validated against laboratory and field data under wave loading. Results show that seabed permeability anisotropy strongly influences solute migration and calcium carbonate precipitation. Low vertical permeability produces broader but shallower precipitation zones, while higher vertical permeability promotes deeper, columnar calcium carbonate precipitation. Wave-induced pore pressure accelerates reaction rate, enhancing precipitation rate and extent. MICP significantly improves liquefaction resistance by increasing shear stiffness (up to 12.86 times) and cohesion (up to 1.21 MPa), thereby forming a stable zone around the grouting pipe. Vertical permeability controls the liquefaction depth through pore-pressure dissipation, whereas horizontal permeability determines lateral precipitation range. A stepped-shape increase relationship is discovered between horizontal permeability and effective protection range. This study offers a validated model to design and optimize microbial shallow grouting for stabilizing anisotropic seabeds in marine engineering.