【作者】 吕春娟；

【导师】 陈丽华；

【作者基本信息】 北京林业大学 ， 生态环境工程， 2013， 博士

【摘要】 为了更好地选择固坡树种,充分发挥根系的固土作用,本研究以材料力学、土力学、弹塑性力学、植物纤维化学等多学科为理论基础,选择我国北方常见油松、白桦、落叶松、蒙古栎和榆树五种树种,模拟根系野外的静荷载和突发的山洪侵蚀、风力作用等动荷载的循环应力作用,分析根系单调抗拉力学特性和循环抗拉力学特性；首次比较系统地从根系的主要化学成分纤维素、木质素、半纤维素含量方面探讨了五种树种去皮根系和带皮根系的抗拉力学特性与主要化学成分关系,以期揭示根系固土的力学基础及其与化学成分的关系。主要研究成果如下：(1)五种树种带皮根系的平均抗拉力和抗拉强度从大到小依次为榆树>白桦>蒙古栎>油松>落叶松；去皮根系抗拉力和抗拉强度从大到小依次为榆树>白桦>蒙古栎>落叶松>油松。五种树种相同直径的去皮根系和带皮根系抗拉强度、抗拉力差异显著。(2)五种树种的抗拉力随直径的增大而增大,均呈幂函数正相关关系,抗拉强度随直径的增大呈现减小趋势,表现出尺寸效应特征,不同树种根系抗拉强度随直径递减函数尚不统一。(3)油松标据、加载速率对抗拉力影响不显著,直径和根皮对抗拉力影响显著；加载速率对抗拉强度影响不显著,直径、标据和根皮对抗拉强度影响显著。(4)五种乔木根系应力-应变曲线特征参数不同,但均为单峰曲线,具有弹塑性材料特征,且直径较小根系的应力应变曲线表现出对外界拉力较强的缓冲能力；三阶抛物线模型能很好地反映其基本特征,五种树种单根单调抗拉的本构模型可综合表示为：式中,E=EO/WP为初始切线模量Eo和峰值割线模量EP的比值,xe屈服点。(5)油松根系低周疲劳后的最大抗拉力和抗拉强度均比疲劳前高,差异显著。根系轴向循环应力-应变滞回曲线表现出明显的周期循环特征,开始阶段滞回环为“稀疏型”排列,滞回曲线并不闭合,随循环次数增加,滞回环间距越来越密集,逐渐闭合,变化趋于稳定。滞回曲线总变形包括弹性变形和塑性变形两部分,塑性变形随循环次数增加逐渐积累,但每一次加荷循环时产生的塑性变形将逐渐减小。(6)五种树种带皮根系与去皮根系的纤维素、半纤维素、综纤维素含量均随直径增大而增大,木质素含量、L/C比值随直径的增大而减小；抗拉力随纤维素、半纤维素、综纤维素含量的增大而增大,随木质素含量、L/C比值的增大而减小；抗拉强度随半纤维素、纤维素、综纤维素含量增大均减小,随木质素含量、L/C比值的增大而增大。根系的抗拉特性是各种化学成分综合作用的结果,可能与根系的显微结构存在很大的关系。(7)不同树种根系极限拉伸应变不同,随纤维素、半纤维素、综纤维素含量的增加呈现减少趋势；随木质素含量、L/C比值的增加呈现增大的趋势。更多还原

【Abstract】 The goal of this study was to reveal root mechanics foundation of soil-reinforcement and its relation with chemical components to choose tree species better for slope stability. Based on material mechanics, soil mechanics, elastic-plastic mechanics, plant fiber chemical science, Roots of Pinus tabulaeformis, Betula platyphylla, Larix principis-rupprechtii, Quercus mongolieus and Ulmus pumila grown in North China were selected as research materials. Root tensile mechanical properties were tested under static loading. Root fatigue mechanical properties were analyzed simulating cyclic dynamic loading such as torrential erosion and wind action et al. Relation between root tensile mechanical properties and main chemical components of cellulose content, lignin content and hemicellulose content were discussed systematically.Major results were summarized as following:(1) The order of average tensile force and tensile strength of the roots with bark in the five species studied was:U. pumilα>B. platyphylla>Q. mongolicus>P. tabulaeformis>L. principis-rupprechtii, while the order of bark-free roots was:U. pumila>B. platyphylla>Q. mongolicus>L. principis-rupprechtii>P. tabulaeformis. The difference of tensile force and tensile strength was significant between bark root and bark-free root.(2)Power function relations were found between root maximum tensile force and root diameter for five trees; while tensile strength was decreased with the increase in root diameter, reflecting a size effect. The functions of five trees’ roots were still not uniform.(3)For P. tabulaeformis, both root length and test speeds had no significant effect on root tensile force, while root diameter and root bark had significant effect on root tensile force. Test speeds had no significant effect on tensile strength; root diameter, root length and root bark had significant effect on tensile strength.(4)For five trees species, the root stress-strain curve parameters were different for different diameters, but all of them were the single-peak curves with elastic-plastic material characteristics, and the stress and strain curve of root with the smaller diameter showed stronger buffer ability to outside loading; The parabolic function of third order could well reflect the basic characteristics of measured stress-strain curve. Root monotonic tensile constitutive model of five trees may be expressed as: Where y is stress, x is strain, E=E0/EP, E0is initial tangent modulus, EP is peak secant modulus, x e is yield point.(5)Root tensile force and tensile strength of P. tabulaeformis were significantly.higher after low cycle fatigue than that without low cycle fatigue Root stress-strain hysteresis curve showed obvious cycle features, at the beginning, hysteretic loop type was arranged for "sparse" but not close; Hysteretic loop spacing was more and more intensive, gradually closed to stability, with the increased circulation number. Total deformation of hysteresis curve included elastic deformation and plastic deformation. Plastic deformation accumulated gradually and each time it constantly decreased with increasing cycles.(6)For five trees roots, cellulose content, hemicellulose content and holocellulose content increased with the increase in diameter, while lignin content and L/C decreased with increasing diameter; Tensile force increased with increased cellulose content, hemicellulose content and holocellulose content, decreased with increased lignin content and L/C; tensile strength decreased with increased cellulose content, hemicellulose content and holocellulose content, increased with the increase in lignin content and L/C. Root tensile mechanical properties were affected by all chemical components and also might be related to root internal structure.(7)Root limiting tension strain was different in five trees; it decreased with increased contents of cellulose, hemicellulose and holocellulose, but increased with increased lignin content and L/C.更多还原