Abstract: The aim of this research is to compare and analyze the reinforcement effect and mechanism of different types of fibers. Four commonly used synthetic fibers, namely, basalt fiber, polypropylene fiber, polyester fiber, and glass fiber, were selected to prepare five groups of reinforced loess specimens for direct shear test by controlling water content, dry density, fiber length, and fiber content. Results demonstrated that: 1) before fiber reinforcement, the curves of shear stress versus shear displacement of loess displayed evident strain softening features; after fiber reinforcement, the strain softening turned into strain hardening. 2) Fibers escalated the shear strength of soil. Among the tested four fibers, basalt fiber has the best reinforcement effect by enhancing the cohesion and internal friction angle of soil by 52.03% and 24.30%, respectively, followed by polypropylene fiber with an increment by 45.94% and 16.01%, respectively. 3)The improvement of the cohesion of reinforced soil is related to the cohesive force of fiber-soil interface and the tensile strength of fiber itself; the increase of internal friction angle is mainly related to the interface friction between fiber and soil. Basalt fiber is of rough surface and large tensile strength, which significantly improves the shear properties of reinforced soil.

Key words: synthetic fiber, reinforced soil, shear strength, tensile strength, sliding friction