【作者】 宋恒川；

【导师】 陈丽华；

【作者基本信息】 北京林业大学 ， 水土保持与荒漠化防治， 2013， 硕士

【摘要】 本文以北川县几种常见的造林树种：柳杉、厚朴、桤木和楠竹的根系为研究对象,通过野外调查和室内试验相结合的方法,对根系的形态特征及分布情况,单根的抗拉力学特性等进行了研究；定性分析了直径、树种等因素对抗拉强度、最大抗拉力和应力-应变关系的影响。之后选取柳杉、厚朴和桤木的根系,进行重塑土直剪试验,对复合体的剪切特性进行研究分析。主要研究成果如下：(1)厚朴根系发达,主根不明显斜向生长且分支多,为斜生根型；桤木主根欠发达,侧根很发达,为水平根型；柳杉侧根数量较多,属复合根型；楠竹根系以竹根为主,均匀分布于基径周围。厚朴的总根长最长,其后依次为楠竹、桤木和柳杉：柳杉不同年龄段根系总长度9年生柳杉>6年生>3年生。(2)各个树种根系主要分布在距地面0-40cm之间。在土层40cm以下,平均根长减小到总根长的10%以下。用根系长度消弱系数描述根系垂直分布特征较理想。用SkethUp模拟出的根系三维立体图,较好的重现了根系的形态分布情况。(3)各树种单根的最大抗拉力随根径的增大而迅速增加,相同直径水平时单根最大抗拉力柳杉>厚朴>桤木>楠竹。不同树种根系的应力应变曲线均为递增曲线,不同的是5mm径级的曲线有较明显的屈服阶段。两个径级下厚朴和桤木的极限延伸率优于柳杉,但是四个树种单根的抗拉强度为：柳杉>桤木>厚朴>楠竹。(4)土体中含有根系时能明显提高土体的抗剪强度,且抗剪强度随根系含量的增加而增加。当有根系存在时,能有效的提高边坡中过量的水分对边坡的不利影响,从而提高土体的抗剪强度和边坡的稳定性。基于无限滑动面模型定量的分析,表明林木的存在能有效的增大边坡的稳定系数,进而增强坡体的稳定性。更多还原

【Abstract】 Taking the roots system of cedar, Magnolia officinalis, alder and bamboo-which were the common specie for afforestation in Beichuan, Sichuan-as research objects, and combineing field investigation with laboratory test, this paper studied the morphology and distribution of root system, and the tensile preperties of a single root; analysed qualitatively the influence of root diameter and species etc. on the tensile strength, the maximum tensile stress and the stress-strain relationship of the root system. Besides, the shear proerties of root-soil composite were studied through the direct sheat test of remolding roots(Japanese cedar, Magnolia officinalis and alder, respectively)-soil composite.The main research results are as follows:(1) The root system of Magnolia officinalis is developed and oblique root typewith a unconspicuous and obliquely growing main root and many branches; the root system of alder is horizontal root type with a undeveploped main root and developed lateral roots; the root system of Cryptomeria fortunei is compound root type with lots of later roots; the root system of bamboo evenly distributed wihtin the basal diameter. The total root of Cortex Magnoliae officinalisis the longest among the research species, and is followed by bamboo, alder and Cryptomeria japonica; Cryptomeria fortunei at9years old is the longest in total root length and is followed by the different ages which is6years old and3years old.(2) The root system of each species is mainly distributed between0to40cm from the ground. The average root length is less than10%of the total root length below the depth of40cm. it is a good method to describe the verticle distribution of root system with the extinction coefficient of root length. The root three-dimensional map by SkethUp can represent the distribution of roots well.(3) For each species, the maximum tensile force increases rapidly with the increacement of root diameter, at the same diameter of a single root, the descending order of the maximum tensile force is Cryptomeria, Magnolia, alder and bamboo. The stress-strain relationship of all the trees is increasing curve, while the curve of5mm in diameter is with an obvious phase. The ultimate elongation of Magnolia officinalis and alder is lager than that of cedar at twoo diameter-class, while the descending order of the single root tensile strength of the four species is; Cryptomeria, alder, Magnolia and bamboo.(4) Root contained in soil can significantly improve the shear strength of soil, moreover, the shear strength increases with the increasing of root content. The existence of roots can effectively reduce the adverse effect of excess water on the slope, so as to improve the shear strengt of soil and the stability of slope. Based on the quantitative analysis of infinite sliding surface model, it is manifest that forests can effectively increase the coefficient of slope stability and enhance the slope stability.更多还原