Dynamic mechanical properties and mesostructure evolution of granular materials subjected to cyclic loading

In this study, a series of biaxial undrained tests of granular materials subjected to cyclic loading were conducted using the discrete element method to investigate the mesostructure evolution from the perspective of a complex network. The mesoscopic parameters, including the average degree, clustering coefficient, and average shortest path length, were used to illustrate the mesostructure evolution of assemblies upon cyclic loading. The results showed that the macroproperties of granular materials have a close relationship with the mesostructure evolution. The amplitude of the axial strain and the pore-water pressure gradually increased with an increase in the number of cycles, whereas the average degree and clustering coefficient decreased. In addition, the amplitude of the average shortest path length varied more drastically. The mesomechanism for the process could be described as follows. In the sample, as the number of contacts and ability to transmit contact force both decreased, the contact network of the assembly became looser and the strength decreased. A larger amplitude for the axial stress led to quicker changes in the pore-water pressure, strain, and mesoscopic parameters. When the value of the normal contact force was regarded as a weight, it was found that the weighted average degree had an approximately linear positive correlation with the mean effective stress. The evolution of the deformation and pore-water pressure could be explored from the mesoscopic viewpoint using the mean weighted ratio of connected triads.