林木根系固土力学特性研究

发布时间：2018-01-22 11:23

  本文关键词： 乔木根系 轴向疲劳拉伸 抗拉强度 三轴压缩试验 土壤抗剪强度　出处：《北京林业大学》2013年博士论文　论文类型：学位论文

【摘要】：森林生态系统中的根系有固持植物体、吸收水分和溶于水中的矿物质的作用,同时还能够阻止浅层滑坡、固持水土。本文通过对华北土石山区4种常见乔木：油松、落叶松、白桦和蒙古栎根系进行轴向疲劳拉伸试验,测定其疲劳前后的抗拉力学特性；分析了直径、树种等因素对根系疲劳前后对最大抗拉力、抗拉强度和应力-应变关系的影响；然后,选取4个树种直径3、5、7mm根系作为试验根样与华北木兰围场取回的土样一起制备成根—土复合体试样,采用全自动三轴压缩仪对复合体进行剪切试验,对复合体的剪切特性进行研究分析,评价根系直径、树种和不同分布方式对土壤抗剪强度的增强作用。 主要研究成果如下： (1)疲劳前4种乔木根系最大抗拉力的平均值大小顺序为：白桦蒙古栎油松落叶松。循环10000次前后油松的抗拉力变化最大,其次是落叶松和蒙古栎,变化最小的是白桦。疲劳后4种乔木根系最大抗拉力平均值大小顺序为：蒙古栎白桦油松落叶松。 (2)4个树种根系疲劳前抗拉强度随着直径的增加而减小,成幂函数关系；4个树种的抗拉强度排序为白桦蒙古栎油松落叶松。经过10000次疲劳拉伸试验后,4种乔木根系抗拉强度顺序是：白桦蒙古栎≈油松落叶松。这与疲劳前顺序基本没有变化,说明疲劳对树种单根抗拉强度有所影响但不足以改变物种本身根系结构组成所造成的影响,树种依旧是影响根系抗拉强度特性非常重要的因素。植物根系在10000次疲劳后的最大抗拉力和抗拉强度均比循环前相同根径的大,说明根系在自然界中的水流或者暴风等破坏力的低周疲劳作用下,自身的抗拉性能不但没有降低,其抗拉性能有不同程度的增加,增强了根系的固土能力。 (3)三轴压缩试验结果表明根系能明显有效地提高土壤的抗剪强度。分布在土体中根系直径增加,根—土复合体的内摩擦角和内粘聚力也随之增大,土壤抗剪强度加强,加根能够明显提高土体抵抗剪切破坏的能力。 (4)根系这种增强作用与根系直径及其在土样中的分布方式有很大关系。复合根复合体抗剪强度值较其他两种分布方式抗剪强度有明显增加。在水平根、垂直根和复合根三种复合体抗剪强度增加顺序基本遵循复合根复合体垂直根复合体水平根复合体。说明复合根在增强土体强度方面效果最为显著,说明植物根系在土壤中形成横纵交错的状态对减少滑坡等自然灾害方面起到更好的作用。
[Abstract]:The roots of the forest ecosystem hold the plants, absorb water and minerals dissolved in the water, and prevent shallow landslides. In this paper, the axial fatigue tensile tests of four common trees: Pinus tabulaeformis, Larix olgensis, Bai Hua and Quercus mongolica were carried out to determine their tensile properties before and after fatigue. The effects of diameter and tree species on the maximum tensile strength, tensile strength and stress-strain relationship before and after root fatigue were analyzed. Then, four tree species with diameter of 3 ~ 5 ~ 5 ~ 7 mm were selected as experimental root samples and soil samples collected from Magnolia chinensis paddock in North China to form root-soil complex samples. The shear test of the complex was carried out with automatic triaxial compression apparatus, and the shear characteristics of the complex were studied and analyzed to evaluate the enhancement of soil shear strength by root diameter, tree species and different distribution patterns. The main findings are as follows: 1) the mean order of the maximum tensile strength of the four tree roots before fatigue was Bai Hua Quercus mongolica larch, and the tensile strength of Pinus tabulaeformis changed the most before and after 10000 cycles. The second was Larix gmelini and Quercus mongolica, and the least change was Bai Hua. After fatigue, the order of the mean values of the maximum tensile strength of root system of four species of Arbor was as follows: Bai Hua larch of Mongolian Quercus mongolica. (2) the tensile strength of four tree species before fatigue decreased with the increase of diameter, and the power function relation; The order of tensile strength of four tree species was Bai Hua Quercus mongolica Larix after 10000 fatigue tensile tests. The order of root tensile strength of four species of trees was Bai Hua Mongolian Quercus 鈮，

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