Dispersive soils are frequently employed as construction materials in projects such as drains and dams in western Jilin, China. However, their propensity to disperse upon contact with water presents a grave threat to construction projects if left unaddressed. Therefore, following the identification of the fundamental physical and chemical properties, as well as the dispersivity of soils in the western region of Jilin Province, Sporosarcina pasteurii was chosen to conduct laboratory experiments and mechanistic studies aimed at improving dispersive soils in the area through MICP. The treatment effect of the soil samples was quantitatively assessed through tests including comprehensive dispersivity identification, unconfined compressive strength (UCS) measurement, and determination of calcium carbonate content. Furthermore, scanning electron microscope (SEM) tests were conducted to examine the microstructural alterations of the soil samples before and after microbial treatment. The experimental results showed that soil dispersion can be significantly reduced under various conditions, and increase the soil strength under certain condition. MICP facilitates the replacement of exchangeable Na+ in soil and induces the formation of calcium carbonate, which fills pores and acts as a cementing agent. Treating dispersive soil in western Jilin is crucial to ensuring the safe and normal operation of its water conservancy projects.

Microbial-induced carbonate precipitation (MICP) is a novel geotechnical reinforcement method that can be used for slope protection, erosion mitigation and seepage control without compromising the soil structure. Based on computed tomography (CT) 3D reconstruction, pore parameters such as the connected porosity, pore equivalent diameter and coordination number are extracted to quantitatively evaluate the effect of the calcium carbonate content on the microstructure of biocemented sand. Then, simulations are conducted to analyze the seepage characteristics of single-phase water flow in the pore space, and 3D visualization of porous seepage in biocemented sand is achieved. The results indicate that as the calcium carbonate content increases, there is a noticeable decrease in total porosity, which is accompanied by an increase in the number of isolated pores and a decrease in the number of connected pores. Concurrently, the average pore equivalent diameter increases, while the pore coordination number decreases. Seepage simulation shows that the permeability of biocemented sand has strong anisotropy, and the pore structure has a strong control effect on the seepage. With increasing calcium carbonate content, the biocemented sand streamlines gradually develop from a network to a branching shape until several main stems remain.