Experimental Study on Solidified Loess by Enzyme-Induced Carbonate Precipitation Combined with Polypropylene Fiber

ABSTRACT Loess disintegration can lead to engineering problems, such as landslides, subgrade settlement, and tunnel deformation. Although enzyme-induced carbonate precipitation (EICP) is considered a novel soil improvement method, only a few studies have applied it to loess soils. Fibers can enhance the strength and improve the brittleness of the soil. Exploring the improvement method of combining EICP with fiber reinforcement is of great significance for its application in loess. In this study, the optimal fiber content of loess was determined by an unconfined compressive strength (UCS) test, and then the fiber-reinforced loess samples were mixed with an EICP solution. UCS, direct shear, disintegration, and scanning electron microscope tests were performed to analyze the strength, water stability, and microstructural characteristics of the loess, with the results indicating that the best reinforcing strength was achieved when the fiber length was 15 mm and the fiber content was 0.6 %. The UCS and shear strength of the EICP-cured fiber-reinforced loess were positively correlated with the calcium carbonate (CaCO3) content, and the generated CaCO3 had a positive effect on the cohesion of the soil and the angle of internal friction. The disintegration test showed that EICP combined with fiber technology improves the disintegration resistance of loess. The specimen hardly disintegrated after treatment with 1.5 mol/L EICP concentration. The CaCO3 generated by the EICP solution further cements the soil particles and fibers, and the fibers provide adhesion nodes for the formation of CaCO3, increasing the contact area between the fibers and soil particles.