Enhancing the structural stability of Pisha sandstone soil is an important measure to manage local soil erosion. However, Pisha sandstone soil is a challenging research hotspot because of its poor permeability, strong soil filtration effect, and inability to be effectively permeated by treatment solutions. In this study, by adjusting the soil water content to improve the spatial structure of the soil body and by conducting unconfined compressive strength and calcium ion conversion rate tests, we investigated the effect of spatial distribution differences in microbial-induced calcium carbonate deposition on the mechanical properties of Pisha sandstone-improved soil in terms of the amounts of clay dissolved and calcium carbonate produced. The results demonstrate that improving the soil particle structure promotes the uniform distribution of calcium carbonate crystals in the sand. After microbial-induced carbonate precipitation (MICP) treatment, the bacteria adsorbed onto the surface of the Pisha sandstone particles and formed dense calcium carbonate crystals at the contact points of the particles, which effectively enhanced the structural stability of the sand particles, thereby improving the mechanical properties of the microbial-cured soils. The failure mode of the specimen evolved from bottom shear failure to overall tensile failure. In addition, the release of structural water molecules in the clay minerals promoted the surface diffusion of calcium ions and accelerated the nucleation and crystal growth of the mineralization products. In general, the rational use of soil structural properties and the synergistic mineralization of MICP and clay minerals provide a new method for erosion control in Pisha sandstone areas.

Traditional soil stabilization methods, including cement and chemical grouting, are energy-intensive and environmentally harmful. Microbial-induced carbonate precipitation (MICP) technology offers a sustainable alternative by utilizing microorganisms to precipitate calcium carbonate, binding soil particles to improve mechanical properties. However, the application of MICP technology in soil stabilization still faces certain challenges. First, the mineralization efficiency of microorganisms needs to be improved to optimize the uniformity and stability of carbonate precipitation, thereby enhancing the effectiveness of soil stabilization. Second, MICP-treated soil generally exhibits high fracture brittleness, which may limit its practical engineering applications. Therefore, improving microbial mineralization efficiency and enhancing the ductility and overall integrity of stabilized soil remain key issues that need to be addressed for the broader application of MICP technology. This study addresses these challenges by optimizing microbial culture conditions and incorporating polyethylene fiber reinforcement. The experiments utilized sandy soil and polyethylene fibers, with Bacillus pasteurii as the microbial strain. The overall experimental process included microbial cultivation, specimen solidification, and performance testing. Optimization experiments for microbial culture conditions indicated that the optimal urea concentration was 0.5 mol/L and the optimal pH was 9, significantly enhancing microbial growth and urease activity, thereby improving calcium carbonate production efficiency. Specimens with different fiber contents (0% to 1%) were prepared using a stepwise intermittent grouting technique to form cylindrical samples. Performance test results indicated that at a fiber content of 0.6%, the unconfined compressive strength (UCS) increased by 80%, while at a fiber content of 0.4%, the permeability coefficient reached its minimum value (5.83 x 10-5 cm/s). Furthermore, microscopic analyses, including X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), revealed the synergistic effect between calcite precipitation and fiber reinforcement. The combined use of MICP and fiber reinforcement presents an eco-friendly and efficient strategy for soil stabilization, with significant potential for geotechnical engineering applications.