Experimental Study on Bio-grouting in Metal Tailings: Injectability, Diffusion Heterogeneity and Strength-Porosity Relationship

Microbially Induced Calcium Carbonate Precipitation (MICP) is an emerging bio-mediated soil improvement technique with potential for sustainable reinforcement of tailings. This study explores the injectability, spatial diffusion characteristics, and mechanical performance of MICP in fine-grained tailings using Sporosarcina pasteurii . A large-scale column grouting apparatus was employed, complemented by dye-tracing, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and triaxial shear testing. Results show that although 93.86% of pores were deemed injectable based on MIP test, dye-tracing experiments revealed significant preferential flow paths, suggesting that pore-throat analysis alone cannot accurately predict grouting uniformity. Mechanical testing indicated that both cohesion and internal friction angle increased with decreasing porosity, with a plateau in friction angle observed below 27%. An artificial neural network (ANN) model was applied to characterize the nonlinear relationship between porosity and shear strength, capturing both the threshold effect and platform stage. These findings offer new insights into pore-scale mechanisms and predictive modeling of strength evolution in MICP-treated tailings.