The Qinghai-Xizang Plateau of China faces challenges like thaw slumping, threatening slope stability and infrastructure. Understanding the mechanical properties of the roots of the dominant herbaceous plant species in the alpine meadow layer of the permafrost regions on the Qinghai-Xizang Plateau is essential for evaluating their role in enhancing soil shear strength and mitigating slope deformation in these fragile environments. In this study, the roots of four dominant herbaceous plant species-Kobresia pygmaea, Kobresia humilis, Carex moorcroftii, and Leontopodium pusillum-that are widely distributed in the permafrost regions of the Qinghai-Xizang Plateau were explored to determine their mechanical properties and effects in enhancing soil shear strength. Through indoor single root tensile and root group tensile tests, we determined the root diameter, tensile force, tensile strength, tensile ratio, and strength frequency distributions. We also evaluated their contributions to inhibiting slope deformation and failure during the formation and development of thermal thaw slumps in the alpine meadow. The results showed that the distribution of the root diameter of the dominant plant species is mostly normal, while the tensile strength tends to be logarithmically normally distributed. The relationship between the root diameter and root tensile strength conforms to a power function. The theoretical tensile strength of the root group was calculated using the Wu-Waldron Model (WWM) and the Fiber Bundle Model (FBM) under the assumption that the cumulative single tensile strength of the root bundle is identical to the tensile strength of the root group in the WWM. The FBM considers three fracture modes: FBM-D (the tensile force on each single root is proportional to its diameter relative to the total sum of all the root diameters), FBM-S (the cross-sectional stress in the root bundle is uniform), and FBM-N (each tensile strength test of individual roots experiences an equal load). It was found that the model-calculated tensile strength of the root group was 162.60% higher than the test value. The model-derived tensile force of the root group from the FBM-D, FBM-S, and FBM-N was 73.10%, 28.91%, and 13.47% higher than the test values, respectively. The additional cohesion of the soil provided by the roots was calculated to be 25.90-45.06 kPa using the modified WWM, 67.05-38.15 kPa using the FBM-S, and 57.24-32.74 kPa using the FBM-N. These results not only provide a theoretical basis for further quantitative evaluation of the mechanical effects of the root systems of herbaceous plant species in reinforcing the surface soil but also have practical significance for the effective prevention and control of thermal thaw slumping disasters in the permafrost regions containing native alpine meadows on the Qinghai-Xizang Plateau using flexible plant protection measures.

Serious riverbank erosion, caused by scouring and soil siltation on the bank slope in the lower reaches of the Tarim River, Northwest China urgently requires a solution. Plant roots play an important role in enhancing soil shear strength on the slopes to maintain slope soils, but the extent of enhancement of soil shear strength by different root distribution patterns is unclear. The study used a combination of indoor experiments and numerical simulation to investigate the effects of varying plant root morphologies on the shear strength of the sandy soil in the Tarim River. The results showed that: (1) by counting the root morphology of dominant vegetation on the bank slope, we summarized the root morphology of dominant vegetation along the coast as vertical, horizontal, and claw type; (2) the shear strength of root-soil composites (RSCs) was significantly higher than that of remolded soil, and the presence of root system made the strain-softening of soil body significantly weakened so that RSCs had better mechanical properties; and (3) compared with the lateral roots, the average particle contact degree of vertical root system was higher, and the transition zone of shear strength was more prominent. Hence, vegetation with vertical root system had the best effect on soil protection and slope fixation. The results of this study have important guiding significance for prevention and control of soil erosion in the Tarim River basin, the restoration of riparian ecosystems, and the planning of water conservancy projects.