Study on creep failure mechanisms and a fractional damage model for hydraulic asphalt concrete

The triaxial creep characteristics of hydraulic asphalt concrete are directly related to the long-term anti-seepage safety of core-wall dams. However, the traditional Burgers viscoelastic constitutive model struggles to balance simplicity with accurate characterization of triaxial creep behavior. To address this issue, this study systematically investigates the creep evolution laws and underlying mechanisms of hydraulic asphalt concrete through both macroscopic and mesoscopic approaches, combining laboratory triaxial creep tests with PFC3D discrete element numerical simulations. At the macroscopic level, experimental results indicate that creep deformation increases significantly with rising stress levels, exhibiting consistent deformation trends under both separate loading and stepped loading modes. During the low-stress steady-state creep stage, confining pressure has minimal impact on creep behavior, while the influence of asphalt content on deformation control becomes more pronounced under high-temperature conditions. Under high stress levels, the vertical strain–time curve distinctly exhibits three characteristic stages: instantaneous, steady-state, and accelerated creep. Mesoscopic discrete element simulations reveal that under low-temperature and low-asphalt-content conditions, the density of strong force chains between aggregate particles is higher, enhancing the material's resistance to deformation. In contrast, under high-temperature and high-asphalt-content conditions, the displacement propagation area of particles expands, with pronounced displacement effects at both ends of the specimen. Stress concentration at the aggregate–mortar interface force chains is identified as the core factor inducing creep damage, providing a mesoscopic basis for introducing a damage evolution mechanism into the model. Based on the classical Burgers model, this study integrates fractional calculus theory and damage mechanics principles to develop a three-dimensional fractional damage creep mechanical model for hydraulic asphalt concrete. This model effectively characterizes instantaneous deformation, the three-stage creep evolution, and the accumulation of mesoscopic damage. It successfully overcomes the limitations of traditional models under complex stress conditions, offering critical theoretical support for long-term deformation prediction and safety design of asphalt concrete core walls in high dams and complex environments.