Uniaxial compression tests on fissured loess after dry-wet cycles were carried out systematically, and the fissure evolution pattern and mechanical properties of fissured loess were deeply investigated. The results show that the surface crack rate R_sc and fractal dimension D_f of samples with different angles increase after more dry-wet cycles, while the growth rate gradually slows down. The dry-wet cycling has no significant influence on the types and characteristics of stress-strain curves; the initial slope of the stress-strain curve declines with the increase of dry-wet cycles. The stress-strain curves of loess samples with different angles all show the characteristics of strain softening, and the samples with 45° show bimodal characteristics. In addition, the uniaxial compression strength of samples with different angles exhibits decelerated attenuation with growing dry-wet cycles. The relationship between uniaxial compression strength and fissure angle unanimously presents characteristics of “double valley” after different dry-wet cycles.

Bentonite modified loess has the potential to serve as a clay liner layer in landfills, but the drying-wetting cycles can cause changes in the permeability and mechanical properties of the bentonite modified loess cushion layer, leading to leakage or instability damage in landfills, posing a threat to the long-term stability of the modified loess cushion layer. Taking plain loess and bentonite modified loess as research objects, experiments were conducted under different drying-wetting cycles, including scanning electron microscopy, mercury intrusion, flexible wall permeability, and uniaxial compression. The effects of dry-wet cycles on the microstructure, anti-seepage performance, and mechanical properties of modified loess were comprehensively analyzed at macro, micro, and nano scales, and the deterioration mechanism of modified loess under drying-wetting cycles was explored. The results show that: Bentonite can be used for loess solidification mainly due to the filling effect and water absorption and expansion characteristics of montmorillonite particles. The pore distribution of plain loess under different drying-wetting cycles is a three peak pore structure, while the pore distribution of modified loess is a bimodal pore structure; The permeability coefficient of plain loess continues to increase with the increase of drying-wetting cycles, while the permeability coefficient of modified loess tends to stabilize after five drying-wetting cycles; The uniaxial compression strength of both plain loess and bentonite modified loess tend to reach a stable value after five dry-wet cycles. Under different drying-wetting cycles, the uniaxial compressive strength of modified loess is higher than that of plain loess.

In this paper, the digital image based triaxial shear test, computed tomography (CT) scanning test and scanning electron microscopy (SEM) test were employed to investigate triaxial shear behavior and microstructure evolution of basalt fiber reinforced loess subjected to drying−wetting cycles. The results show that the shear failure mode of soil samples with relatively higher basalt fiber content changes from overall bulging failure to shear band failure with the increase in the number of drying−wetting cycles, while the shear failure mode exhibits an opposite trend with the increase in the fiber content at the early stage of drying−wetting process. Neither drying−wetting cycle nor fiber content has obvious effect on the type and characteristics of stress−strain curves, and both of them present strain-hardening behavior. The deviatoric stress at failure decreases with the increasing number of drying−wetting cycles; however, the attenuation rate gradually decreases. The deviatoric stress at failure first increases and then decreases with the increasing fiber content, showing a parabolic variation, and the optimal fiber content is 0.6%. A similar trend is observed between the ME value of CT scanning and the deviatoric stress at failure. Drying−wetting action induces cracking and loosening around the soil-fiber interface, thus weakening the fiber reinforcement effect. However, compared with unreinforced loess, fiber reinforced loess demonstrates strong overall stability in its microstructure. The macroscopic and microscopic damage variables reflecting the drying−wetting induced deterioration of loess samples were finally established, which shows a consistent variation trend.