寒旱环境灌木根系增强边坡土体抗剪强度特征

为深入研究根系与剪切面呈不同夹角α条件下,边坡土体中根系对土体抗剪强度的影响,以及定量分析评价植物根系对边坡土体抗剪强度的增强作用,该项研究以生长期为150 d的柠条锦鸡儿、霸王根系及其组成的柠条锦鸡儿根-土复合体、霸王根-土复合体为研究对象分别进行室内单根拉伸试验和复合体剪切试验。通过对2灌木根系进行单根拉伸试验,得到2种灌木根系单根的抗拉强度,并对根系与剪切面夹角α分别为45°、60°、75°、90°等4种条件下的根-土复合体进行剪切试验,得到4种α角度条件下的根-土复合体试样抗剪强度;在此基础上,分析探讨了单根抗拉强度与根-土复合体试样粘聚力值之间的关系。结果表明:柠条锦鸡儿根系的单根抗拉强度较霸王根系的单根抗拉强度略高;柠条锦鸡儿根-土复合体、霸王根-土复合体试样,在4种不同α角度条件下的黏聚力均显著大于素土黏聚力;当α角由45°增大至90°时,2种灌木根-土复合体的黏聚力值呈逐渐增大的趋势,且黏聚力的增长率亦表现出一致性变化规律,即2种灌木根-土复合体试样的黏聚力的增长率均随着α角的增大而呈增大趋势;根-土复合体黏聚力值与单根抗拉强度存在正相关关系。由上述复合体黏聚力值的变化规律反映出,试验区2种灌木根系对边坡土体抗剪强度具有显著增强作用,同时亦反映出随根系的单根抗拉强度的增大,根系对土体粘聚力值的增强效果相对愈加显著,且随根系与剪切面间夹角不同,根系增强边坡土体抗剪强度贡献具有不同的变化规律,即表现在根系与剪切面之间的夹角趋于垂直时,根系具有相对最大限度地增强土体抗剪强度的作用。该研究结果为定量评价植物根系增强边坡土体抗剪强度的贡献,提供了试验方面的数据支撑,这为进一步深入探讨植物根系增强边坡土体抗剪强机理提供参考。

Characteristics of slope soil shear strength reinforced by shrub roots in cold and arid environments

The Xining Basin, located in the transition region between the northeastern Qinghai-Tibet Plateau and the west of the Loess Plateau, has been chosen as the testing area. C. korshinskii (Caragana korshinskii Kom.) and Z. xanthoxylon (Zygophyllum xanthoxylon (Bunge) Maxim.), which are planted in a self-established plot and have a growth period of 150 d, have been taken as the tested samples. Tensile test of single root and shear test have been conducted on the roots of C. korshinskii and Z. xanthoxylon and the root-soil composite systems (root of C. korshinskii and soil, root of Z. xanthoxylon and soil) respectively. By tensile test of single root, tensile strength of single root for the 2 kinds of shrubs has been obtained. Meanwhile, shear test to root-soil composite systems with the inclination between roots and shear plane of 45, 60, 75 and 90° has been carried out, and the shear strength of the 2 kinds of root-soil composite systems under the 4 different inclinations has been obtained. On this basis, the relationship between the tensile strength of single root of 2 kinds of shrubs and the cohesion force of 2 kinds of root-soil composite systems has been discussed, and the contribution of shrub roots to soil shear strength has been quantitatively analyzed. The results of tensile test of single root and shear test of root-soil composite system show that the tensile strength of single root has a relatively close relationship with the root diameter, and the root tensile strength of single root for C. korshinskii (44.84 MPa) is slightly greater than that for Z. xanthoxylon (37.52 MPa). The cohesion forces of root-soil composite systems for C. korshinskii and Z. xanthoxylon with the inclination of 45, 60, 75 and 90° are 9.90, 11.68, 12.97, 13.92 and 8.73, 11.27, 12.61, 13.96 kPa respectively, and all of them are greater than that of soil without roots which is 6.41 kPa. The cohesion force of 2 kinds of root-soil composite systems shows an increasing trend with the inclination increasing from 45 to 90°, and the incremental rate of cohesion force exhibits the same increasing trend. Moreover, the cohesion force of root-soil composite systems is positively correlated with the tensile strength of single root, which indicates that the cohesion force of root-soil composite system increases with the root tensile strength increasing. Variation of cohesion force of root-soil composite system reflects that roots play a key role in increasing shear strength of slope soil in the testing area, and another conclusion has also been obtained that increasing the tensile strength of single root significantly increases the shear strength of root-soil composite system. And the contribution of roots in increasing shear strength of slope soil varies with the variation in inclination; the incremental rate of cohesion force of root-soil composite system for C. korshinskii increases from 54.45% to 117.16%, and for Z. xanthoxylon increases from 36.19% to 117.78% with the inclination increasing from 45 to 90°. Therefore, as the roots are perpendicular to the shear plane, they play the most significant role in increasing the shear strength of roots. The results can be used as an instruction in quantitatively assessing the contribution of roots in increasing the shear strength of slope soil, and are helpful in the further investigation of the mechanism of the roots in increasing the shear strength of slope soil.