Study On The Distribution And Mechanical Properties Of Root System Of Four Tree Species In Beichuan County

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.