Effects of drying–wetting cycles on small-strain stiffness characteristics of fissured clay

Fissured clays exhibit unique geotechnical behaviors, with the stiffness characteristics evolving dynamically in response to environmental changes. To address this issue, reported here is a systematic assessment of how drying–wetting (DW) cycles affect the small-strain stiffness characteristics of fissured clay. Resonant column tests are taken to examine the nonlinear attenuation behavior of the small-strain shear modulus (SSSM) and damping ratio of fissured clay under various DW cycle and consolidation pressure (25–200 kPa) conditions. Scanning electron microscopy (SEM) and computed tomography (CT) are employed to reveal the microstructure of fissured clay. The Hardin–Drnevich (H-D) model is used to describe the decay law of its SSSM, and the small strain stiffness characteristics of fissured soil are analyzed in view of damage mechanics. The results show that the SSSM of the fissured clay decreases as the DW cycles increase, with the greatest attenuation at original soil state. The damping ratio exhibits an incremental trend with escalating strain and a higher number of DW cycles. Regarding damage, DW cycles can lead to the formation of microcracks in the sample, and the aggregates disperse into smaller aggregates, which then aggregates again, resulting in structural damage. The damage variables of the samples under various confining pressures and DW cycles are analyzed based on the principle of strain damage. Finally, the volume changes and the distribution of different pore sizes obtained through CT are analyzed to investigate the stiffness attenuation under DW cycles. Additionally, the study examines the propagation direction of secondary cracks induced by primary fissures, which will play an important role in reduction of the stiffness. Our investigations contribute to understanding of soil mechanics and practical applications in areas where fissured clay is prevalent.