Enhancing mechanical strength of Yili loess soil using microbial-induced calcite precipitation (MICP)

Loess soils widely distributed in the Ili River Valley of Northwest China face severe risks of soil erosion and geological hazards due to their strong collapsibility, high soluble salt content, and loose structure. This study explores an environmentally friendly bio-improvement strategy—Microbial Induced Calcium Carbonate Precipitation (MICP) technology—to enhance the mechanical properties and structural stability of Ili loess. Through laboratory experiments, the effects of calcium ion concentration in the cementing solution (0.5, 1.0, 1.5 mol/L) and the number of cementing cycles (1, 3, 5 cycles) on the improvement efficacy were systematically analyzed. Results from unconfined compressive strength tests, triaxial shear tests, and scanning electron microscopy (SEM) revealed that the calcium carbonate precipitates generated during the MICP process effectively filled soil pores and cemented soil particles, significantly improving the soil's macromechanical properties. Compared to the untreated control, the optimal treatment group (calcium ion concentration 1.5 mol/L, 5 cementation cycles) exhibited increases of 2.46%, 63.64%, 79.70%, and 18.31% in internal friction angle, cohesion, unconfined compressive strength, and shear strength, respectively. This study confirms that MICP technology fundamentally improves the engineering properties of problematic loess through biomimetic mineralization, providing a sustainable solution for regional soil and water conservation and ecological slope reinforcement. • First MICP application to saline Yili loess yielding 82.1% ↑ unconfined compressive strength. • Optimized MICP (1.5 M Ca²⁺, 5 cycles) achieves 20.3% ↑ shear strength under UU conditions. • The differences in improvement effects between Yili loess and other loess types are discussed.