Abstract: To investigate the shear mechanical properties of straw fiber reinforced loess, we conducted triaxial shear tests and scanning electron microscopy tests. These tests aimed to examine the influence of fiber content, fiber length, and soil moisture content on the shear-strain characteristics and shear strength of the reinforced loess, as well as the reinforcing mechanism. The results of the tests demonstrate that the addition of straw fibers significantly enhances the shear strength of loess by increasing soil cohesion. Importantly, the admixture of straw fibers does not alter the type and characteristics of the deviatoric stress-strain curve of loess, which remains strain-hardening in nature. Through further analysis, we determined that the optimal values for fiber content and length are 0.3% and 10 mm, respectively. Beyond these optimal values, an excessive number of weak interfaces within the soil mass would weaken the integrity of the reinforced loess. Consequently, the bond and friction between the fibers and soil decrease, leading to a decline in the shear strength of the reinforced loess. Additionally, we found that the best moisture content for reinforced loess coincides with the optimal moisture content of pure loess. However, if the moisture content of reinforced loess exceeds this optimal value, a thickening water film forms on the surfaces of the fibers and soil. This, in turn, increases lubrication and reduces friction between the fibers and soil, ultimately resulting in a decrease in the shear strength of reinforced loess.

Key words: reinforced loess, straw fiber, triaxial test, scanning electron microscope, mechanical characteristics