【作者】 杨璞；

【导师】 岑章志； 胡夏嵩；

【作者基本信息】 清华大学 ， 力学， 2008， 博士

【摘要】 植物根系在土壤中穿插、缠绕和网络,与土壤形成了一种天然的复合材料,对防止水土流失具有重要作用。人类有意识的通过种植植物进行固土护坡已有数百年的历史,但是对植物根系加固土壤的力学机理并不完全了解,仍有很多问题值得进一步研究。本文对青海省黄土高原地区优势固土护坡植物进行实地考察,发现受干燥气候等自然条件的影响,植物根系具有向深处生长的特性,并且在土壤中排布比较规则,可以被简化为周期性分布的长纤维增强复合材料。本文从复合材料细观力学的角度,对植物根系加固土壤的力学机理进行了数值计算和实验研究。基于复合材料细观力学的均匀化理论和广义平面应变假设,本文提出了一种周期性长纤维复合材料代表性胞元的数值计算方法,通过选取复合材料横截面的代表性胞元作为研究对象,体现复合材料的细观结构特征,同时引进宏观尺度和细观尺度,构造基于细观摄动位移插值的广义平面应变单元,并建立了代表性胞元的弹塑性增量有限元计算格式。考虑到界面的非理想粘接,本文发展了一种基于细观摄动位移插值的广义平面应变界面单元,并建立了计算非理想界面复合材料胞元的数值计算格式。本文在青海省对根土复合体的力学特性进行了实验研究,设计了一种周期性长纤维根土复合体三轴试验的实验方法,考虑到根土复合体试验的特殊性,提出了一种根土复合体试样制作的新方法,并对含根体积比为0.5%和1%的根土复合体进行了三轴试验,得到了根土复合体在0.01MPa围压下的轴向极限载荷和破坏模式。实验还测得了单根和素土的材料参数,并测得了实验现场原状土的含根体积比,为根土复合体的数值计算进行了准备。采用非理想界面周期性复合材料胞元极限载荷的数值计算方法,本文建立了含根体积比为0.5%和1%的根土复合材料代表性胞元的有限元计算模型,对根土复合体的三轴试验进行了数值模拟,数值计算结果与实验值比较吻合。并计算了不同加载角度根土复合体的极限载荷,分析了影响根土复合体极限载荷的若干因素。更多还原

【Abstract】 The vegetation roots play a very important role in reducing soil erosion by means of being embedded in, entangled in and enwrapped in soil. The vegetation have been used to improve shallow slope stability and reduce geological disasters for several hundreds years. However, the mechanical mechanism of the soil-roots composite is still not very clear today. In Loess Plateau, Qinghai Province, China, the roots of vegetation grow unidirectional and arrange periodically, so the soil and the roots can be considered as a kind of homogeneous long fiber reinforced composites. In this dissertation, the mechanical mechanism of soil-roots composites is studied through numerical simulation and experimental study.Based on the homogenization theory and generalized plane strain assumption, a kind of numerical method to analysis the homogeneous long fiber reinforced composite is established. A representative volume cell is chosen to reflect the microstructure of a periodic composite. By introducing the macroscopic and microscopic scale, the generalized plane strain element is constructed based on microscopic fluctuation displacement. The corresponding elas-plastic incremental finite element equation is established. In the state of generalized plane strain, a kind of interface element is developed based on microscopic fluctuation displacement to simulate the weak interface between the matrix and the fiber. And the corresponding numerical method is established.The properties of soil-root composites were obtained in experiments conducted in Qinghai Province. A kind of experimental method for the limit load of the soil-root composites was proposed. The sample preparation process was modified for the soil-roots composites. In the experiment, two soil-root composites specimens with the root fraction of 0.5% and 1%, respectively, were submitted to triaxial test. The limit loads and failure mode were obtained. In addition, the basic properties of the roots and the natural soil were measured from experimental tests for the numerical simulation. The finite element models of the representative volume cell are established based on the numerical method proposed in this dissertation. The numerical limit loads of soil-root composites are obtained and compared with the experimental values. Good agreement of limit loads has been achieved between the numerical and the experimental results. The relationship between limit loads and the angle of load is obtained. And the effects of material parameters on limit loads are also studied.更多还原