There are many drawbacks in traditional loess-strengthening technology. MICP (microbially induced calcium carbonate precipitation) technology provides a new approach to loess management, but there are few studies on loess solidification and a lack of engineering application research and verification. This study investigated the strength and microscopic mechanisms of loess solidified by the application of MICP technology combined with plant straw. The permeability conditions of loess for MICP technology were derived, and multiple sets of experiments were conducted using specific loess, Bacillus pasteurii, cementing solution, plant straw, and other materials. The experiments explored shear strength, unconfined compressive strength, microscopic properties, plant growth adaptability, and factors affecting bacterial growth. The results indicated that within the temperature range of 25–35 °C, the concentration and urease activity of Bacillus pasteurii were significantly affected by temperature, with the highest bacterial concentration observed at 30 °C. During scaled-up cultivation, increasing the inoculation ratio prevented a significant decrease in the urease activity of individual bacterial strains, and a 1% inoculation ratio was generally sufficient to meet the experimental requirements. When the loess density was 1.7 g/cm³ and 1.8 g/cm³, the cohesive force and internal friction angle in the experimental groups with added bacterial solution were increased by approximately 30% and 50% and 15% and 5%, respectively, indicating that MICP technology can significantly enhance the shear strength of loess.

Through three stress path tests of unsaturated Ili undisturbed loess, the effect of soluble salt content on the deformation of net mean stress, suction, and deviated stress were investigated. The mechanical properties of the normalized compression curve, soil water characteristic curve and critical state line were revealed. The test results indicate that: in the isotropic compression test, the normal compression curves controlling different suctions can be characterized by using the initial void ratio and the yield net mean stress, and can be described as a two-parameter exponential function. In the triaxial shrinkage test, the soil water characteristic curves controlling vary net mean stresses are dimensionless by using saturated moisture and air entry value, and the normalization formula can be characterized by a single parameter exponential function. In the consolidation shear test, the corresponding effective net mean stress is calculated by suction and saturation. The critical state lines under the unsaturated condition controlling vary suctions can be described as the critical state line under the saturated condition on the plane of effective net mean stress and deviator stress. When the effective net mean stress is constant, the critical state lines under the unsaturated condition can be characterized by the degree of gas saturation and the ratio of unsaturated void ratio to saturated void ratio. The research will offer reference pointing at the regulation and utilization of water and salt in the loess region of Central Asia, so as to better guarantee the sustainable development of saline-alkali land project construction.