Shallow slope failures occur frequently in the Loess Plateau region and the ecological materials are usually used for slope protection. The mechanical characteristics and strength models of the interface between environmental protection materials and native materials are crucial for evaluating the effectiveness of slope protection. In this study, the polypropylene fiber and guar gum are used for slope protection, and indoor experiments are conducted to elucidate the mechanical performance changes at the interface between untreated loess (UL) and guar gum-treated fiber-reinforcement loess (GFL) under different moisture content and curing time. A damage strength model of the interface between untreated loess and guar gum-treated fiber-reinforcement loess (UL-GFL) is constructed based on statistical damage theory. The results show that guar gum can aggregate and cement loess particles, while polypropylene fiber enhances the friction between loess particle aggregates. The synergistic effect of these two materials significantly improves the strength and hydraulic characteristics of loess. The cohesion and internal friction angle of the interface between untreated loess and guar gum-treated fiber-reinforcement loess decrease with an increase in moisture content and increase with an extended curing time, stabilizing when the curing time exceeds 7 days. The strength model for the interface of untreated loess and guar gum-treated fiber-reinforcement loess is established. The proposed model is verified through experimental data based on the stress-displacement relationship. The findings of this research can provide an important reference for the application of ecological protection materials on loess slopes.
