Rockfill, as the predominant constituent of rockfill dams, experiences cyclic loading and unloading due to fluctuations in water levels during dam operation. This cyclic loading induces irreversible deformation accumulation, leading to excessive dam deformations, slope instability, and concrete panel cracking. The objective of this study is to investigate the mechanical behavior of rockfill under low-frequency cyclic loading and unloading, and propose a constitutive model that accounts for this loading condition. To overcome the limitations of laboratory tests, Tests were conducted employing the Combined Finite and Discrete Element Method (FDEM). An FDEM model incorporating particle shape and breakage was established and meticulously calibrated through laboratory triaxial tests. Subsequently, cyclic loading and unloading tests were performed under various confining pressures, stress levels, and cycles number. The results exhibited the presence of hysteresis loops within the designated range of confining pressures and stress levels, with pronounced influences on their shape and magnitude. As the number of cycles increased, the hysteresis loops gradually transformed from elliptical to leaf-shaped, accompanied by a diminishing rate of irreversible plastic strain accumulation. Notably, the maximum plastic strain was observed during the initial loading process. The test findings obtained through FDEM demonstrated excellent agreement with laboratory tests, thereby validating the capability of FDEM in simulating low-frequency cyclic loading and unloading. Leveraging the invaluable loading and unloading data acquired through FDEM, an enhanced constitutive model applicable to rockfill under low-frequency cyclic loading and unloading was developed within the framework of generalized plasticity. This model effectively captures the hysteresis loops and accumulation of residual deformation resulting from multiple loading cycles. This study presents a novel approach for acquiring data on rockfill under low-frequency cyclic loading and establishes a robust constitutive framework for accurately predicting deformations of rockfill dams subjected to cyclic water loading conditions.
 

Rockfill,FDEM,particle shape,cyclic loading and unloading,Constitutive model