Shear behavior of basalt fiber modified compacted red mudstone as subgrade fill material

Abstract This study experimentally investigated the shear behavior of basalt fiber-modified compacted red mudstone as a subgrade of a high-speed railway. We examined the effects of different vertical stresses, initial water contents, and fiber contents on brittleness and dilatancy. Several direct shear tests were conducted under the aforementioned conditions. The stress displacement curve tended to vary from softening to hardening with an increase in vertical stress. In the Mohr–Coulomb mode, except for the saturated state, the residual internal friction angle was greater than the peak value, whereas the residual cohesion was lesser than the peak value. The maximum cohesion occurred at the optimal water and fiber content, whereas the friction angle exhibited a downward trend with an increase in the contents discussed above. The brittleness index ( I b ) was defined as the ratio of the peak to residual shear strengths. The magnitude of the brittleness index reduced with increase in the vertical stress. Moreover, the maximum value occurred at the optimal water and fiber content. Furthermore, the deformation mechanism was discussed based on the dilatancy angle( ψ ). Based on the data, three different stages were proposed: Softening–Dilatancy (S1), the Hardening–Dilatancy (S2), and Hardening–Shrinkage (S3).