Shear creep characteristics of carbonaceous shale under coupled hydro-mechanical-chemical coupling: Macroscopic-microscopic behavior

: The shear creep characteristics and microstructural evolution of carbonaceous shale under the coupled effects of oxalic acid corrosion and rainfall-induced dry-wet seepage cycles are crucial for elucidating the failure mechanisms of mine slopes containing weak carbonaceous shale interlayers. This study used a self-developed THMC-B (Thermo-Hydro-Mechanical-Chemical-Blasting) multi-field coupled shear rheology system, scanning electron microscope (SEM), and pores/particles and cracks analysis system (PCAS) to investigate these characteristics and evolution. The results indicate that, compared with the natural state (without oxalic acid corrosion or dry-wet seepage cycles), the coupled effects of acid corrosion at pH 1 and 12 dry-wet seepage cycles lead to a maximum reduction of 42.63% in long-term strength, an increase of 305.74% in the steady-state creep rate at the final stress level, and a rise in porosity from 1.07% to 20.83%. Both the fractal dimension and probability entropy of pores increase significantly after damage, which verifies the computational statistical analysis of strength degradation. The failure mode transitions from being controlled by the intact cementation between mineral particles to being dominated by friction and slip induced by damage. The coupled effects of acid corrosion, dry-wet seepage cycles, and osmotic pressure synergistically promote and exacerbate the damage to carbonaceous shale. The shear creep characteristics of carbonaceous shale exhibit a strong negative linear correlation with its fracture properties. These findings provide new insights into the degradation mechanisms of carbonaceous shale in complex acidic water environments, with critical implications for the assessment of mine slope stability.