Abstract: Vegetation roots can effectively enhance the shear strength of near-surface soils, and root reinforcement has become an important measure to improve shallow slope stability in ecological slope protection engineering. This study employs the discrete element method to construct a refined three-dimensional root system model and investigate the mesoscopic mechanisms governing the evolution of shear behavior at the root-soil interface. The influence of different inclined shear angles (5°, 10°, 15°) on the shear mechanical response of root-reinforced soil is systematically examined, and, under three levels of vertical stress, the evolution of shear strength, the shear resistance contribution of different hierarchical roots, and the distribution of taproot tensile stress are analyzed. The results show that the shear strength of root-reinforced soil increases significantly with vertical stress, shear angle, and root area ratio on the shear plane. The confinement provided by lateral and fibrous roots contributes most to shear resistance, and their relative roles adjust with changes in shear angle. The axial tensile stress in the taproot develops in a staged manner with increasing vertical stress and shear angle and is most effectively mobilized under a shear angle of 10°. This study elucidates the reinforcement mechanisms of hierarchical root systems under inclined shear and provides a reference for the mechanical design of ecological slope protection.

Key words: root reinforcement, inclined shear test, discrete element method, shear strength, hierarchical roots