Experimental study on improving hydraulic characteristics of sand via microbially induced calcium carbonate precipitation

Microbially induced calcium carbonate precipitation (MICP) technology has garnered significant attention for enhancing soil engineering properties, presenting a potential alternative to traditional cementitious materials for soil seepage control. This study investigates the application of MICP to enhance the hydraulic characteristics, specifically reducing porosity and hydraulic conductivity, of loose sandy soils. Three types of sand-river sand, sea sand, and quartz sand-underwent MICP treatment in cylindrical molds using multiple treatment schemes. Laboratory experiments, including permeability tests, porosity tests, scouring and soaking resistance tests, microstructural testing and analysis, and microfluidic chip tests, were conducted to evaluate the hydraulic characteristics and microstructure contributing to sealing. The results revealed that the structural integrity of the MICP-treated sand declined with an increase in cementation solution (CS) concentration, which were then categorized into intact, discontinuous, and loose blocks. The average decreases in porosity and hydraulic conductivity were 5.5% and 97.2%, respectively, from 0.382 and 4.33 × 10^-4 m/s (before treatment) to 0.361 and 1.2 × 10^-5 m/s (after treatment). Three cementation patterns, G-C-G, G-G, and G-C, were identified in the MICP-treated sand, with corresponding pore-filling rates decreasing successively. Furthermore, the study explores the feasibility of individually distinguishing and characterizing the contributions of biofilms and calcium carbonate precipitation to the reduction in porosity and permeability in biocemented sand through simulation.