Shear creep characteristics and fractional modeling of carbonaceous shale under thermo-hydro-mechanical coupling

Gently inclined weak interlayers, which commonly occur in high mine slopes, are typically composed of carbonaceous shale. Owing to its low strength and pronounced sensitivity to temperature and moisture fluctuations, carbonaceous shale readily softens and undergoes creep deformation. Therefore, an in-depth understanding of its creep behavior is essential for landslide prevention in mining areas. In this study, the effects of temperature cycling and initial water content on the creep behavior of carbonaceous shale were systematically investigated through direct shear and creep tests. Based on the Caputo fractional derivative theory, a fractional-order creep model was established, and a nonlinear damage model considering temperature and initial water content was further developed. The results show that carbonaceous shale with high water content is prone to argillization during shearing, resulting in a loose fracture structure. Premature fracture propagation and weakened cementation markedly reduce its shear strength. The creep process can be divided into three stages: initial creep, steady-state creep, and creep rupture. Both the creep rate and creep deformation increase with increasing number of temperature cycles and initial water content. Compared with the classical Nishihara model, the proposed thermo-hydro-mechanical (T-H-M) coupled damage creep model provides higher fitting accuracy. Sensitivity analysis and experimental validation further confirm that the proposed model can accurately characterize the creep behavior of carbonaceous shale under T-H-M coupled damage conditions.