The geogrid-soil interaction, which is crucial to the safety and stability of reinforced soil structures, is determined by the key variables of both geogrids and soils. To investigate the influence of backfill and geogrid on their interface behavior of the reinforced soil retaining walls in Yichang of Shanghai-Chongqing- Chengdu high-speed railway, a series of laboratory pullout tests were carried out considering the influence of water content and compaction degree of the backfill as well as tensile strength of the geogrid. The development and evolution law of pullout force- pullout displacement curves and interface characteristics between geogrid and soil under various testing conditions were analyzed. The results showed that with increasing water content, the geogrid pullout force decreased under the same pullout displacement. The interfacial friction angle of the geogrid-soil interface showed a slowly increasing trend with increasing water content. The variation of the interfacial friction angle ranged between 9.2 degrees and 10.7 degrees. The interfacial cohesion, however, decreased rapidly with increasing water content. With increasing degree of compaction, the interfacial friction angle and the interfacial cohesion of the geogrid-soil interface gradually increased. The change of the interfacial cohesion with the compaction degree was more significant. When the degree of compaction increased from 0.87 to 0.93, the interfacial cohesion increased around 7 times. The tensile strength of geogrid has certain influence on its pullout force-pullout displacement relationship. High-strength geogrid could significantly improve the mechanical properties of the geogrid-soil interface. The investigation results can provide some reference for the design and construction of geogrid reinforced soil structures.

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.