<p>Incorporating sand with waste tire rubber as a new geotechnical material offers an effective solution to the global challenge of waste tire pollution. To investigate the complex mechanical behaviors of sand-rubber mixtures, DEM modeling of the sand-rubber mixtures, considering the realistic shape of particles and the deformability of rubber fibers is performed in this study. Microscopic parameters in the DEM are obtained through a comprehensive calibration process with results from the direct shear test, sliding test, and uniaxial tensile test. Next, a series of direct shear tests are simulated with sand-rubber mixtures of different rubber mass fractions and normal stresses, and the macroscopic behaviors, i.e., shear stress and volumetric strain of mixtures, are analyzed. At the microscale, the particle displacement fields, contact forces, internal forces of rubber fibers, and rubber fiber deformation are presented and investigated. In particular, a novel descriptor is proposed to assess the bending deformation of rubber fibers. The findings of this work enhance our comprehension of the mechanical behavior of sand-rubber mixtures and contribute to their application in engineering practices.</p>