中文摘要：

通过在试验区将4种护坡灌木植物种植在PVC管内，分别对土体、4种灌木根-土复合体试样做直接剪切试验，对比非含根土体与4种灌木含根系土体抗剪强度指标，评价试验区生长时间为1a灌木根系的护坡力学效应；通过对比4种灌木根-土复合体抗剪强度，评价生长时间为1a的4种灌木根-土复合体的护坡力学强度增强效应。试验结果表明：（1）4种灌木根-土复合体当其含根量、含水量一定时，抗剪强度随垂直压力的增大而呈线性增大，表明试验区灌木根-土复合体抗剪强度与剪切面上的法向压力成正比，且符合库仑定律；（2）4种灌木根-土复合体的黏聚力显著大于素土的黏聚力，而内摩擦角妒的变化不显著；（3）四翅滨藜、柠条锦鸡儿、霸王、白刺灌木根-土复合体的黏聚力与素土相比，其增长幅度分别是76．3％，62．7％，45．8％，22．0％。试验区灌木根-土复合体剪应力与剪切位移关系反映出灌木根-土复合体受剪力作用开始段近似线性，接近剪破时呈圆滑曲线，达到剪破后近似为水平线，灌木根-土复合体剪应力随着垂直压力的增大而呈显著增加趋势；剪应力的增大开始阶段基本呈线性，接近剪破时呈非线性。根据试验区4种灌木植物根-土复合体强度，它们的护坡贡献按由大至小分别是：四翅滨藜、柠条锦鸡儿、霸王、白刺。

英文摘要：

Four shrubs planted in PVC pipes in the testing areas are studied; then direct shear tests on the undisturbed soil and root-soil composite system are conducted. By comparing the shear strength indexes of the soil without root and four kinds of soils with roots, the mechanical effects of the root system of four shrubs with one-year growth period on slope protection can be evaluated. Comparison between the shear strengths of fourshrub root-soil composite systems is made to evaluate the enhancement effect of the systems for slope protection. The results show that： （1） when the root and water contents of the four-shrub root-soil composite systems keep constant, the shear strength increases linearly with increasing vertical pressure, indicating that the direct shear strength of the root-soil composite systems agrees with Coulomb law; （2） the cohesion of the root-soil composite systems is obviously larger than that of soil without roots, and there are no apparent changes in the internal friction angle; （3） compared with the cohesion of soil without roots, the increasing amplitudes of the cohesion of Atriplex canescens, Caragana korshinskii, Zygophyllum xanthoxylon, Nitraria tangutorum are 76.3 %, 62.7%, 45.8% and 22.0% respectively. The relations between the shear strength and displacement of the root-soil composite systems show a linear relationship at the beginning stage of the shear process, a rounding curved relationship at the end of the shear process, and an approximate horizontal relationship when shear failure. The shear stress of the root-soil composite systems increases obviously with increasing vertical pressure, in which the increasing rule of shearing strength agrees with linear relationship at the beginning of the shearing process, basically linear at the beginning and nonlinear when approaching failure. According to the strengths of the four-shrub root-soil composite systems, the mechanical effects of the four one-year growth period shrubs for slope protection are as follows： Atriplex can