Abstract: Fibers effectively improve the mechanical properties of soil. In this paper, the influences of glass fiber content, fiber length, curing age, and drying-wetting cycles on the shear mechanical properties of fiber-straw ash-lime improved composite loess were examined through unconsolidated and undrained triaxial shear tests. Results demonstrated that with the addition of fiber, the stress-strain curve of the improved soil gradually displayed strain hardening features. With the rise of fiber content and fiber length, the ultimate deviatoric stress, cohesion and internal friction angle first increased but then decreased. The optimal ratio is that the fiber content is 0.4% and the fiber length is 9 mm. Under drying-wetting cycles, the ultimate deviatoric stress, cohesion and internal friction angle of the improved soil decayed gradually; the rate of such decay was large in the early stage and tended to be stable in the later stage. The decay amplitude was obviously affected by fiber content and fiber length. Regardless of the number of drying-wetting cycles, the strength and stability of the composite improved soil enhanced with the expansion of curing age

Key words: composite improved loess, shear mechanical properties, wet and dry cycles, glass fiber content, fber length, curing age