Root anchoring provides nonnegligible assistance to prevent soil erosion and stabilize slopes. The anchoring ability of plants suffers a tremendous impact from the soil conditions and the root characteristics. To reveal the root reinforcement effect, a group of pullout tests was conducted on five different tree root systems (Pinus tabulaeformis, Betula platyphylla, Larix gmelinii, Quercus mongolica, and Ulmus pumila) with different soil moisture contents and soil dry weights. The results indicate that the root property (species, diameter, and tensile strength) and soil condition (water content 9.72%, 12.72%, 15.72%, 18.72%, and dry weight 1.32 g/cm³, 1.42 g/cm³, 1.52 g/cm³) had a significant effect on the anchoring effect of the soil. The anchoring effect is more obvious for the roots with a larger diameter and higher tensile strength. With the increase in the soil water content and the dry weight, the root system is more prone to failure but the root anchoring effect of soil with an optimum soil water content performs the best. Among the five different tree species, Pinus tabulaeformis roots were the least effective in anchoring the soil and Betula platyphylla roots performed the best.

In dealing with issues such as soil erosion and slope instability, plant roots enhance the shear strength of the soil mass through their anchoring effect. However, in nature, cyclic loads such as flash floods and blizzards indirectly impose fatigue effects on plant root systems. To explore the impact of cyclic loads on the anchoring capacity of plant roots, this paper selects the roots of Betula platyphylla as the research object and uses a monotonic load and cyclic load as two loading modes. Under different loading amplitudes (25%, 50%, and 75%), root diameters and burial depths (50 mm, 100 mm, and 150 mm), and soil moisture contents (11.85%, 13.85%, and 15.85%), the effects of each factor on the anchoring capacity of the roots under cyclic loading are analyzed. The results showed that the root–soil interface exhibited two failure modes under different cyclic load amplitudes, and the cyclic load significantly reduced the maximum friction of the root–soil interface. As the cyclic load amplitude increased (from 25% to 75%), the hysteretic curve envelope area increased, and the growth rate of cumulative residual slip changed from decreasing to decreasing and then increasing. A good correlation was found between cumulative residual slip and the number of loading cycles, and the three characteristic slips were correlated with loading amplitude but not significantly with diameter. The increase in soil moisture content, root embedment depth, and diameter led to an increase in the ratio of the two maximum friction forces. It was shown that a certain degree of plasticity exists at the root–soil interface to resist environmental stresses in nature. At high fatigue stress levels, the root–soil interface is more nonlinear, and as the load amplitude increases, more energy is dissipated, and bond damage between the root–soil interface becomes more pronounced. The root–soil interface gradually degraded under long-term cyclic loading, whereas the increase in root depth and soil water content could resist the negative effect of cyclic loading on anchorage capacity, and the resistance effect became more and more obvious with the increase in diameter.

Global warming and the increasing frequency of extreme heat events pose significant challenges to the stability of vegetation-stabilized slopes. The mechanisms by which temperature variation influences the mechanical properties of root-reinforced soil remain insufficiently understood. This study developed a thermo-mechanically coupled hypoplastic constitutive model that incorporated root reinforcement mechanisms. To comprehensively verify model reliability, temperature-controlled consolidated undrained triaxial tests were conducted on root-reinforced soil. The experimental program considered multiple root contents over a temperature range from 20 to 60 °C. Additional experimental data reported in the literature were also adopted for external validation. Experimental results show pronounced thermal softening at elevated temperatures. The ultimate shear strength at 60 °C decreased by approximately 29.4% compared with 20 °C conditions. Despite this reduction, root reinforcement maintained relatively high absolute soil strength under high-temperature conditions. Comparisons between model predictions and both experimental results from this study and published data demonstrated the reliability of the proposed model. Furthermore, parameter sensitivity analysis revealed that strength enhancement exhibits diminishing marginal gains with increasing root content, indicating the existence of an optimal root content ratio. This study investigates the thermo-mechanical coupling mechanism of root-reinforced soil and provides tools for engineering design under extreme climatic conditions.