Rubber-sand mixtures (RSM), characterized by low unit weight, strong elastic deformation ability, good durability, and high energy dissipation, hold significant potential for civil engineering applications. However, research on the time-dependent dynamic behavior remains relatively scarce, limiting their broader application in practical construction. A thorough understanding of this behavior is critical for ensuring long-term performance of RSM across various engineering contexts. In the study, the effects of rubber's thermal aging and loading history, two key factors of time-dependent behavior, on the dynamic properties of RSM under small to medium strains were investigated. Aging of rubber particles was accelerated through oven aging experiments, followed by resonant column tests to determine the dynamic shear modulus and damping ratio of RSM samples with rubber particles of varying aging levels (5 %, 10%, 15 %, and 20% rubber content). Furthermore, multiple load tests were also conducted on the same samples to assess the impact of loading history on RSM's dynamic properties. The results reveal that thermal aging causes volumetric expansion and a reduction in compressive strength of rubber particles, leading to changes in the dynamic shear modulus and damping ratio of RSM. Specifically, the dynamic shear modulus initially decreases during early aging stages, then increases, eventually stabilizing, while the damping ratio consistently decreases with prolonged aging. With repeated loading cycles resulting in a reduction in dynamic shear modulus and an increase in damping ratio. These results improve our understanding of this composite's long-term behavior and offer practical advice for its use in seismic isolation and geotechnical engineering.

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.

The undrained cyclic behavior of rubber-sand mixture (RSM) is usually investigated under the cyclic loads with unidirectional shear stress. However, bidirectional shear stress exists in many engineering practices subjected to complex loads, under which the liquefaction resistance of soil may be overestimated. Furthermore, the soil behavior under bidirectional shear stress exhibits quite differently from that under unidirectional shear stress. Therefore, undrained cyclic behavior of RSM under bidirectional shear stress should be further investigated. In this study, several specimens made by RSM with different rubber contents (from 10 % to 30 % by volume) are consolidated under two conditions, K0 consolidation and the combination of K0 consolidation with consolidation shear stress (CSS). Subsequently, numerous tests are conducted under the unidirectional and bidirectional cyclic loading paths to investigate the cyclic undrained behavior of RSM. The results show that the bidirectional shear loads incur a larger normalized pore water pressure (PWP) than unidirectional shear loads. In addition, an energy-based method is employed to understand the relationship between cumulative energy and normalized PWP. During the stage of rapidly accumulating PWP, the dissipated energy required to generate the same normalized PWP is identical, and it is independent of the shapes of loading paths.

A series of numerical true triaxial compression tests were carried out on rubber-sand mixtures (RSMs) by means of the 3D discrete element method to study the effect of the intermediate principal stress ratio b on the failure properties of RSMs with different rubber contents (RCs), and to explore the effect mechanism from a microscopic point of view. The numerical simulation results show that as the intermediate principal stress ratio b increases and the peak deviator stress qpeak gradually increases, while the peak internal friction angle phi b first increases and then decreases. The numerical simulation results were compared with four common strength criteria, including the modified Lade-Duncan criterion, the SMP criterion, the FKZ criterion and the DP criterion. The comparative analysis showed that the existing common criteria cannot accurately predict the damage state of RSMs, suggesting the necessity for further research. At the micro level, the combined effects of the intermediate principal stress ratio b values and RC on the micro-parameters, such as the coordination number, average normal stress between particles, probability density and anisotropy, were investigated.

In the present study, a number of triaxial tests were conducted to examine the shear behavior of rubber-sand mixtures, with an emphasis placed on the critical-state line and energy performance. The experimental results indicated that under otherwise similar conditions, the deviatoric stress reduces with increasing rubber content but increases with increasing confining pressure. The promotion of confining pressure and rubber content contributed to increased contractiveness of rubber-sand mixtures (RSM) in shear. The position of the critical-state line (CSL) in the e-lnp ' plane depended on both rubber content and confining pressure, and it shifted toward the right (or upward) direction with an increase of confining pressure and rotated in a clockwise direction with an increase of rubber content. The slope of the critical-state line (M) in the q-p ' plane decreased as the rubber content increased. In addition, the energy analysis indicated that most work input is dissipated, with the stored elastic potential energy taking a minor proportion. The energy dissipation decreased with increasing rubber content and increased with increasing consolidation pressure. Macroscopically, this was associated with the stress level within a specimen and microscopically linked with the contact force level and related energy dissipation through the interparticle friction behaviors.