Study on delayed breakage and time-dependent deformation of rockfill particles

The creep behavior of rockfill materials is a key mechanism influencing the long-term deformation of rockfill dams post-construction, with direct implications for structural integrity and operational safety over decades. Traditional investigations rely primarily on intricate indoor creep tests that demand specialized facilities. These tests are not only costly and time-intensive—requiring substantial financial investment, advanced equipment, and prolonged durations from days to weeks—but also constrained by limitations in scalability. Empirical time parameters derived from small-scale laboratory samples often encounter difficulties when applied to full-scale dam predictions due to issues such as scaling effects, mismatched boundary conditions, and the inability to replicate realistic in-situ stress environments. In response, computational micromechanical simulations, particularly those employing advanced particle-scale techniques like the discrete element method, have emerged as a promising alternative. Once developed, such models offer significant reductions in both economic and time costs, while also addressing the dimensional and boundary constraints of physical testing. These simulations enable realistic representations of granular behavior and the modeling of geological timeframes beyond the reach of conventional laboratory methods, yielding valuable micromechanical insights. The fundamental physical mechanism underlying rockfill creep arises from the combined influence of sustained gravitational self-weight and long-term external loading, which induces time-dependent fracturing within individual rock particles. This fracture process is initiated by stress concentrations at inter-particle contacts and inherent flaws within the rock fragments, leading to the generation of finer particles that fill interstitial voids and promote complex frictional sliding between adjacent grains. These mechanisms result in a continuous rearrangement of the particle framework, expressed as progressive macroscopic deformation under constant loading conditions. Internal force redistribution renews local stress concentrations, triggering successive cycles of particle breakage, void compaction, intergranular sliding, and structural reorganization. This cyclic evolution persists until internal stresses fall below the critical fracture threshold, ultimately approaching a theoretical state of terminal creep equilibrium. Precise characterization of the time-dependent mechanical behaviour of individual rockfill particles—particularly their delayed fracture response under sustained load—is thus essential for accurate micromechanical modeling of rockfill creep. To this end, this study conducts experimental investigations using constant-load compression tests, wherein uniaxial compressive stress is applied to individual particles over prolonged durations. This test aims to isolate and quantify the time-dependent fracture characteristics of individual rockfill particles. Results indicate that once the applied stress exceeds a critical threshold—approximately 85% of the particle’s short-term compressive strength—delayed fragmentation occurs with statistically significant consistency. The fracture time exhibits an inverse exponential relationship with stress magnitude: as the applied stress increases beyond this threshold, the time to failure decreases sharply, reflecting a characteristic exponential decay pattern associated with stress-accelerated fracture dynamics. Although time-dependent deformation under constant load remains minimal for individual particles, delayed fracture contributes substantially to the cumulative creep deformation of rockfill assemblies. This behaviour has been effectively represented using the Nishihara rheological model, which combines elastic, viscoelastic, and viscoplastic components to capture the interplay of instantaneous response, transient retardation, and time-dependent viscous flow. The model’s temporal parameters demonstrate a clear sensitivity to stress level, offering a mechanistic explanation for delayed fracture evolution. These findings—especially the stress-dependence of time-delayed failure—provide critical input parameters for initiating accurate numerical simulations of complex creep phenomena, thereby enhancing long-term performance predictions and supporting the broader adoption of computational approaches in dam engineering.