Physical-mechanical properties of microbially induced calcite precipitation-treated loess and treatment mechanism

Loess disintegration can lead to geotechnical engineering problems, e.g., slope erosion, wetting-induced landslide, and hydroconsolidation. Microbially induced calcite precipitation (MICP) technique is a potential loess reinforcing method. This study investigated the physical-mechanical properties of MICP-treated loess and then explored the mechanism of loess modification by MICP. Here, loess first underwent MICP treatment, i.e., mixing loess with Sporosarcina pasteurii and cementation solution (CS). Then, the effects of the CS concentration (0.2, 0.6, 0.8, and 1 M) on the physical and mechanical properties of the MICP-treated loess were tested. Finally, the static contact angle test, scanning electron microscopy (SEM), and X-ray diffractometry (XRD) were conducted to study the mechanism of MICP treatment on loess. Results showed the following property changes of loess after MICP treatment: the liquid limit decreased by 1.7%, the average particle size increased from 6 to 47 μm, the specific gravity decreased from 2.65 to 2.43, the unconfined compressive strength increased from 37 to 71 kPa, and the disintegration time increased from 10 to 25 min. Besides, the shear strength also increased, and the shear strength parameters (cohesion c and internal friction angle \varnothing ) varied with the CS concentration. The static contact angle tests indicated that the water absorption ability of loess was reduced after MICP treatment. SEM and XRD results verified that the CaCO₃ from MICP was attributed to the above results. The above findings explained the mechanism of MICP treatment of loess: the CaCO₃ coats and cements the particles, and fills the pores of loess, improving the strength and water stability of loess.