A study of the mechanical properties of herbaceous roots and root-soil composite systems in the degraded alpine pasture artificially restored grassland

To study the reinforcement to soil by herb roots along the Qinghai-Tibet railway, an artificially restored grassland along the Qinghai-Tibet railway is selected as test site. By conducting tensile tests to a single root and direct shear tests to the root-soil composite system with its growth period of one year, such mechanical indices as roots’ tensile strength and shear strength of root-soil composite system are quantitatively assessed. The results show that the values of the mean root diameter, tensile resistance and tensile strength for the combination I (Agropyron cristatum + Puccinellia distans + Poa crymophila) are greater than those for the other combinations. Moreover, a positive power function can be introduced to describe the relationship between the root diameter and its tensile resistance for the three species, while a negative power function is introduced to describe the relationship between the root diameter and its tensile strength. In addition, the cohesion of the root-soil composite system for the three species exhibits a decreasing trend with the increasing soil depth. Of the values for cohesion for the three species, the cohesion for the combination I is 32.62 kPa, greater than that of the other two combinations by 15.3 % and 57.7%, respectively, suggesting the excellent capacity in reinforcing soil. The results may provide a theoretical basis for the prevention and control of the alpine grassland degradation, soil erosion, shallow landslides and other geo-hazards and eco-hazards along the Qinghai-Tibet railway, and are of a practical guiding significance for ecological restoration by planting vegetation along the railway.