Analysis of Macroscopic and Mesoscopic Shear Characteristics of the Interface between a Geogrid and a Rubber–Sand Mixture under Normal Cyclic Loading

Rubber–sand mixtures (RSM) have the potential to be used as eco-friendly geotechnical materials for the reinforcement of roadbeds and other projects. By a series of monotonic direct shear tests under normal cyclic loading (NCMDS), the impact of rubber contents, initial stresses, stress amplitudes, and loading frequencies on the shear properties of the geogrid and RSM interface was studied. Shear models for pure sand and RSM were formulated using PFC3D, and the mesoscopic behaviors during the shearing were investigated. The findings indicated that the interface exhibited prominent softening characteristics. It was observed that a lower rubber content corresponded to a more pronounced softening phenomenon. For a given rubber content, with a rise in frequency, there was a decline in both the peak stress and stress fluctuation amplitude of the interface, and the overall dilatancy decreased. The RSM had slightly more contact points than pure sand, and the count of contact points during the peak state surpassed that during the valley state. Throughout the shearing, the coordination showcased cyclic fluctuations. The coordination near the interface initially diminished, then gradually leveled out, mirroring the macroscopic dilation effect. Under cyclic loading, the kinetic energy of particles exhibited more pronounced fluctuations compared to the damping energy, and the damping energy in RSM exceeded that in pure sand.