黄土丘陵区灌草植物固土护坡过程中根系破坏机理试验研究

The Loess Plateau is the most serious soil erosion area in China. Vegetation measure with shrub and herb plants is an effective method for conserving soil and water in this area. During studying on mechanical effects of soil reinforcement and slope protection by shrub and herb plants, inadequate root failure mechanism, including unclear superior failure pattern and its controlling factors, and incomprehensive determination indexes and methods of root failure, restricts the establishment and application of mechanical models of root reinforcement. Based on cultivation tests, root tensile tests, root pull-out tests and direct shear tests in laboratory, root failure mechanism in soil reinforcement and slope protection by shrub and herb plants in the loess hilly area will be studied. The failure processes and types of roots in shearing soils reinforced by plants will be revealed. The principle and criterion of each root failure type will be clarified. The laws of root failure during soil reinforcement and slope protection by plants will be discussed and summarized. The systematic indexes for describing root failure mechanism will be established. The project can provide basic theory for further study on mechanical mechanism of root reinforcement and scientific basis for slope protection by vegetation measures in the Loess Plateau.

黄土高原水土流失严重，灌草植物措施是黄土高原保持水土的有效手段。灌草植物固土护坡的力学效应研究中，根系破坏机理的优势破坏模式及控制因素尚不清楚，根系破坏的判定指标与方法尚不完善，导致植物根系固土力学模型的建立与应用受到制约。本申请项目针对黄土丘陵区灌草植物根系，拟开展室内栽培试验、根系轴向拉伸试验、拉拔试验和根系-土壤复合体直剪试验等多种试验，进行根系破坏机理研究，揭示根系在植物固土护坡土壤剪切时的破坏过程和模式，阐明各破坏模式发生的原理及符合的破坏准则，探讨并总结植物固土护坡过程中根系的破坏规律，建立描述根系破坏机理的系统指标。本研究可为深入研究植物根系固土力学机制提供理论基础，为黄土高原植物固土护坡工程提供科学依据。

为研究黄土区灌草植物根系破坏机理机理，通过对紫花苜蓿和沙棘开展根系拉伸试验、拉拔试验、根系-土壤复合体直剪试验来研究黄土丘陵区灌草植物固土护坡过程中根系破坏的机理。主要研究成果如下：（1）紫花苜蓿根系直径、数量和横截面积随根系埋深增大而减小，并且根系直径随根系长度增加而减小且满足幂函数关系。（2）紫花苜蓿根系能有效增强浅表层土体的极限抗剪强度，其对土体极限抗剪性能的增强效应随土壤含水量增加而降低。（3）对于同一剪切深度、土壤含水量接近的条件下，根土复合体试样抗剪强度随着根面积比(RAR)增加而增大，相比裸地试样，根土复合体试样剪切位移增加了15 mm左右。（4）根系在拉拔过程中存在拉断和拔出两种破坏模式，其中拔出破坏的L-S曲线分为三段：弹性变形段、根-土连接破坏段、根系脱离段。（5）根系在拉拔过程中存在极限根径，紫花苜蓿的极限根径范围为0.30-0.40 mm，沙棘的极限根径为0.86 mm，当直径小于极限根径时，根系更容易发生拉断破坏；反之，根系更容易发生拔出破坏。（6）根系直径与最大抗拔力呈正幂函数关系，与根-土摩擦系数和拉拔能量呈正相关关系，并且拔出破坏的拉拔能量大于拉断破坏。（7）随着根系埋深的增大，拉拔能量逐渐增大，最大抗拔力不断增大且两者呈线性关系。（8）最大抗拔力与根-土摩擦系数随埋置角度的增大呈先增后减的趋势，当埋置角度为60°时达到峰值。（9）紫花苜蓿与沙棘最大抗拔力与根-土摩擦系数随土壤含水量的增大呈先增后减的趋势，而拉拔能量随土壤含水量的增大呈先增后减的趋势。（10）最大抗拔力随土壤密度的增大呈正幂函数关系，拉断率、根-土摩擦系数和拉拔能量随土壤密度的增大而显著增大。（11）紫花苜蓿与沙棘根系最大抗拉力、抗拉强度、弹性模量与根系直径呈正幂函数关系，最大抗拉力随根系数量和水平间距的增加呈幂函数关系，抗拉强度随根系数量与水平间距的增加呈指数函数关系。