Microbial-induced calcite precipitation (MICP) is one of the environmentally friendly techniques that has recently become popular amongst geotechnical engineers. Two bacterial species of Bacillus family, i.e., B. pasteurii and B. megaterium have been used to improve the loess soil properties. A set of unconfined compressive, permeability, ultrasonic, and collapse potential tests have been applied to assess the characteristics of natural soil compared to those of MICP-treated ones. The effects of curing time (1, 3, and 7 days), bacterial optical density (OD = 0.5, 1, and 1.5), and soil density (13, 14, and 15 \( \frac{kN}{m^3} \)) have been investigated. Results indicate that biological enhancement has improved the engineering properties of the loess soil. MICP-treated soil using B. megaterium provides higher strength improvement ratios (1.15–4.4 times) rather than B. pasteurii-treated samples (1.05–3.4 times). Correspondingly, specimens containing B. megaterium have greater permeability reduction ratios (3.9–93.7%) compared with those of B. pasteurii ones (2–95%). Moreover, scanning electron microscope (SEM) analysis has been employed to confirm the findings. It is worth noting that various bacteria concentrations, curing periods, and soil densities can affect the stress-strain curve considerably. The results indicated that MICP reduced the collapse potential between 24 and 54.8% and increased the longitudinal wave velocity between 1.1 and 2.4 times more than the untreated soil.

微生物引起的方解石沉淀（MICP）是一种环保技术，最近在岩土工程师中变得很流行。芽孢杆菌家族的两种细菌，即巴斯德毕赤酵母和巨大芽孢杆菌已被用于改善黄土的土壤特性。与经MICP处理的天然土壤相比，已使用一组无限制的压缩，渗透性，超声波和坍塌潜力测试来评估天然土壤的特性。固化时间（1、3和7天），细菌光密度（OD = 0.5、1和1.5）和土壤密度（13、14和15 \（\ frac {kN} {m ^ 3 } \））已被调查。结果表明，生物增强改善了黄土的工程性质。使用巨大芽孢杆菌经MICP处理的土壤提供了更高的强度改善率（1.15-4.4倍），而不是经过巴氏芽孢杆菌处理的样品（1.05-3.4倍）。相应地，与巴斯德毕赤酵母相比，含有巨大芽孢杆菌的标本的通透性降低率更高（3.9–93.7％）（2-95％）。此外，已采用扫描电子显微镜（SEM）分析来确认发现。值得注意的是，各种细菌浓度，固化时间和土壤密度都会对应力-应变曲线产生很大影响。结果表明，与未经处理的土壤相比，MICP降低了24％至54.8％的坍塌潜力，并使纵向波速提高了1.1至2.4倍。