This study aims to systematically investigate the shear strength and freeze-thaw damage of the root-soil complex in the Shisifenzizi and Xijin Section of the Yellow River embankment in Inner Mongolia of China. The optimal range of root cross-sectional area ratio was also determined to quantitatively analyze the impact of water level on the stability of ecological slopes. Root diameter and quantity were balanced to improve the soil shear strength and freeze-thaw resistance. A series of tests were conducted in engineering practice, including direct shear, freeze-thaw cycle and indoor single-root tensile tests. A systematic analysis was implemented to explore the effects of water content (w), confining pressure (σ), root diameter (D), root number (N), and root cross-sectional area ratio (RAR) on the shear strength (τ) of slope soil under freeze-thaw conditions. The freeze-thaw resistance of each key factor was evaluated after investigation. A slope instability model was established to quantify the impact of water level on the slope stability. The experimental results indicated that: 1) Root systems were effectively enhanced the shear strength of soil, in terms of the cohesion (c) and internal friction angle (φ). Compared with bare soil, the bond strength of the root-soil complex increased by 2.77%-36.2%, and the internal friction angle increased by 7.56%-26.29%, indicating the improvement effect of the roots on soil mechanical properties. 2) The internal friction angle of soil slightly increased, as the number of freeze-thaw cycles (n) increased, while the shear strength and bond strength significantly decreased. Shear strength, bond strength, and internal friction angle were inversely proportional to the water content, while directly proportional to confining pressure, indicating the coupling relationship between freeze-thaw damage and water and stress states. 3) Shear strength, bond strength, and internal friction angle first increased and then decreased, as the number of roots, root diameter, and root cross-sectional area ratio increased. The optimal range of root cross-sectional area ratio was 0.733% - 0.942%, indicating an optimal root configuration to maximize the reinforcement. 4) The sensitivity of each factor to freeze-thaw damage resistance (Dτ) was ranked in the descending order: confining pressure ranks first, root diameter and root number are in the middle, and water content ranks last. Freeze-thaw damage resistance decreased with increasing water content, while it increased with increasing confining pressure. Furthermore, it first increased and then decreased with increasing root diameter and number. The best freeze-thaw resistance was achieved with the root diameter of 4 mm and the number of roots of 7. 5) The slope safety factor (K) first increased and then decreased with the increase in the number of roots, root diameter, and root section ratio. Once the river water level was lower than the groundwater level, the safety factor was greater, indicating that the lower river water level was beneficial to slope stability. Therefore, the optimal range of root section ratio was provided for the vegetation slope reinforcement. The root diameter and number of roots were considered to improve the bidirectional shear strength and freeze-thaw resistance during laying. The findings can provide a scientific basis for river slope protection in cold regions.

To improve the utilization efficiency of aeolian sand, this study investigates the influence of varying calcium carbonate whisker volume fractions on the compressive and splitting tensile strengths of aeolian sand concrete. Scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) were employed to examine the interfacial bonding between whiskers and cement paste and to elucidate the strengthening mechanism. Based on the experimental results, a theoretical model of relationships among compressive strength, splitting tensile strength and curing age was established. The findings show that the incorporation of an appropriate amount of calcium carbonate whiskers significantly improves pore structure and mechanical performance. When the aeolian sand content is 60%, the optimal whisker volume fractions for compressive strength and splitting tensile strength are 0.15% and 0.20%, respectively. The proposed predictive model aligns well with the experimental data and effectively predicts strength development with age.