Shear strength characteristics of loess solidified via enzyme induced calcium carbonate precipitation (EICP) and fiber reinforcement (FR)

Loess has a porous, weakly cemented, and loosely consolidated structure, making it prone to collapsibility, disintegration, and dissolution, which consequently lead to slope instability, foundation settlement, and ground fissures. Enzyme induced calcium carbonate precipitation (EICP) method could significantly enhance strength and lead to the brittle failure of solidified soil, whereas harden effect of the fiber reinforcement (FR) be able to help enhance the ductility. In this paper, the loess was solidified via EICP with combination of polypropylene fiber reinforced (PFR) or wool fiber reinforced (WFR). According to conducting unconsolidated undrained triaxial tests, how fiber type ( FT ), fiber length ( FL ), and fiber content ( FC ) influence the shear strength and index of brittleness ( IB ) of solidified loess were investigated. Furthermore, the microstructure of loess was constructed and the solidification mechanism was revealed by performing XRD, FTIR, and SEM tests. Based on the triaxial test results, an EICP-FR shear strength model was constructed by taking into account the impact of fiber length, fiber content, and fiber diameter. Test results indicated that stress-strain curves showed the trend of strain softening and the peak deviatoric stress of EICP-FR treated loess is remarkably larger than that of EICP treated loess. As both fiber length and fiber content increased, the peak deviatoric stress increased, whereas the index of brittleness decreased. For EICP-PFR treated loess, the optimal reinforcement conditions was FL = 12 mm and FC = 0.75%, and that of EICP-WFR treated loess was FL = 12 mm and FC = 1.00%. Untreated loess had a loose structure due to the poor bonding effect, and the particle aggregates and the compactness between soil particles were significantly increased under EICP effect. A single fiber was anchored to soil particles, and the anchor effect of WFR was better than that of PFR. The model calculation results exhibited good agreement with the test results, indicating that the model is applicable to predicting the shear strength of loess solidified by EICP-FR. The findings can provide substantial guidance for the practical application of loess solidification engineering.