Effect of hydroxypropyl methylcellulose (HPMC) modified microbial induced carbonate precipitation on strength and water stability of loess

Loess exhibits high sensitivity to water, rendering it susceptible to strength loss and structural destruction under hydraulic effects of rainfall, irrigation and groundwater. As an emerging soil improvement technology, microbial induced carbonate precipitation (MICP) stands out for its cost-effectiveness, efficiency, and environmental sustainability. In this study, hydroxypropyl methylcellulose (HPMC) was innovatively introduced into the MICP process to improve the strength and water stability of loess, and a set of unconfined compressive strength (UCS), direct shear, laser particle size analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were conducted. The results show that HPMC-modified MICP is able to generate a novel structural matrix combining organic and inorganic elements, significantly enhancing the strength, stiffness, and ductility of loess. HPMC protects loess from water erosion by forming viscous membranes on the surfaces of soil particles and calcium carbonate crystals. Increasing HPMC content can augment membrane viscosity, which is conducive to stabilizing the loess structure, but it has the negative effect of reducing inter-particle friction through increasing membrane thickness. As the HPMC content increased to 0.6%, the strength loss of loess under high water content decreased. These findings are expected to provide critical support for the engineering application of HPMC-modified MICP in loess improvement.