Mechanical properties and enhanced soil shear strength of herbaceous plant roots in the alpine meadow layer of the permafrost region on the Qinghai–Xizang Plateau, China

he QinghaiXizang 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 QinghaiXizang 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 speciesKobresia pygmaea, Kobresia humilis, Carex moorcroftii, and Leontopodium pusillumthat are widely distributed in the permafrost regions of the QinghaiXizang 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 WuWaldron 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: FBMD (the tensile force on each single root is proportional to its diameter relative to the total sum of all the root diameters), FBMS (the crosssectional stress in the root bundle is uniform), and FBMN (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 FBMD, FBMS, and FBMN 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 25.9045.06 kPa using the modified WWM, 67.0538.15 kPa using the FBMS, and 57.2432.74 kPa using the FBMN. 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 QinghaiXizang Plateau using flexible plant protection measures.