Mechanical properties of porous weakly cemented rocks under alternating creep-fatigue action

During underground engineering projects, siltstone—a porous, weakly cemented rock—commonly undergoes cyclical states of creep and fatigue, raising questions about its mechanical stability under such conditions. To investigate, this study employed laboratory experiments, featuring a creep-fatigue alternation action test and uniaxial reloading test, with the absolute expansion stress serving as the upper load limit. Results reveal a counterintuitive synergy between creep and fatigue actions. Fatigue processes reduced the viscoplastic deformation capacity of siltstone, prolonging its creep rupture life. Besides, creep actions amplified the fatigue life of siltstone by over 168%, attributable to the filling and embedding of rock debris particles in the rock matrix. Additionally, siltstone’s elastic modulus and Poisson’s ratio displayed a periodic “rise-drop” oscillatory pattern under the creep-fatigue regime. Plastic strain values emerged as a robust metric for quantifying damage. Intriguingly, creep-fatigue alternation increased the absolute expansion stress by 11.7%, bolstering the rock’s damage resistance. However, this cyclical regime exacerbated the postpeak fracture behavior of siltstone, underscoring the complexity of its mechanical response.