A study of the mechanic strength of vegetation roots for roadbed slope protection in the Tuotuohe river region along the QinghaiTibet railway

The Tuotuohe river region roadbed slopes lying along the QinghaiTibet railway were taken as the testing area, and Elymus nutans was planted at both sides of the slopes. The pullout resistance was obtained by the in situ pullout test in the testing area where fiveyear growth period Elymus nutans was planted at both the shading and the solar roadbed slopes, and the pullout resistance value was obtained. The pullout resistance value for solar roadbed slope is 3088 N and 2352 N for shading roadbed slopes, which shows that the soil moisture is the key factor affecting the roots’ pullout resistance. The longer shining time, the stronger intensity, and the larger evaporating amount of the solar slope contribute greatly to the different soil moisture in the solar and shading slopes. There exists a linear relationship between the pullout resistance and the fibrous roots quantity, the roots diameter, the roots length, the aboveground biomass tall, the number of tillering and the roots surface area. The higher increasing amplitude exists between the pullresistance and the fibrous roots quantity in the solar roadbed slope, which is obviously larger than that in the shading roadbed slope. When the number of fibrous roots ranges from 40 to 60, the roots pullout resistance value of solar roadbed slope is between 11 N and 25 N, the roots pullout resistance value of the shading roadbed slope ranges from 8 N to 15 N; when the number of fibrous roots ranges from 60 to 140, the roots pullout resistance value of solar roadbed slope is between 30 N and 70 N, and the roots pullout resistance value of shading roadbed slope is between 20 N and 50 N. According to the roots mechanical strength of Elymus nutans, the mechanical contribution for slopes stability of Elymus nutans planted at the solar roadbed slope is relatively greater than that in the shading roadbed slope. The achievements can provide a theoretical guide for the research region and areas with the same ecological and geological environments for sowing herb species seeds for slope protection with vegetation.