Study on the influence of joint roughness on time-dependent shear properties

Experimental evidence confirms that initial damage significantly influences rock creep behavior; however, existing creep models rarely account for instantaneous shear damage induced during shear loading. In this study, multi-stage shear creep tests are conducted on artificial sandstone joints with quantified three-dimensional morphologies under constant normal stress. Results demonstrate that joint roughness parameter E ( θ *| θ *>0 ° )- μ , shear stress level τ / τ p , and normal stress σ n significantly influence the time-dependent shear properties. The degradation of shear resistance, analyzed through its roughness and frictional components, elucidates the mechanism behind the reduction in the long-term shear strength ratio with increasing roughness and normal stress. A novel non-stationary viscoelastoplastic shear model for rough joints is established, explicitly incorporating the time-dependent evolution of shear damage. Within this model, the instantaneous shear damage variable ( D ) governs the subsequent evolution of creep damage, and the derived equivalent shear stress ( τ ′ ) is identified as the key driver of time-dependent shear displacement. Strong concordance between experimental measurements illustrated in the other paper and theoretical predictions validates the model’s predictive efficacy. • Multi-stage shear creep tests on artificial sandstone joints with quantified 3D roughness elucidate the influence of the roughness parameter E ( θ *| θ *>0 ° )- μ , shear stress level τ / τ p , and normal stress σ n on time-dependent shear behavior. • The concepts of an idealized joint and equivalent shear stress ( τ' ) are introduced, identifying τ' acting on undamaged micro-units as the key driver of time-dependent viscoelastic and viscoplastic displacement. • The degradation mechanism of the long-term shear strength ratio ( ξ ) is elucidated by decomposing shear resistance into roughness and frictional components, revealing that higher roughness and normal stress lead to a more pronounced time-dependent reduction in the shear strength. • A non-stationary viscoelastoplastic shear model is developed, explicitly incorporating the instantaneous shear damage incurred during initial loading as a governing factor for subsequent creep evolution. • The model demonstrates strong predictive capability against independent experimental data. A damage evolution index ( α ) is defined, which quantifies the transition between creep hardening, stability, and accelerating failure, providing practical guidance for engineering predictions on rough joints.