Fundamental And Mechanical Study On Soil Reinforcement And Slope Protection By Woody Plant Roots

In this dissertation, vertical distribution types of Robinia pseudoacacia and Pinus tabulaeformis were analyzed by field and laboratory experiments and theoretical analysis. Root tensile properties of five woody plants were tested by axial tensile tests. The relation of Pinus tabulaeformis root diameter and tensile property was studied. The effects of sampling time, species, root length and test speed on maximum tensile force and tensile strength of roots were also evaluated. And then effect of different layout of roots in soil samples on soil reinforcement was assessed with triaxial compression test. Finite element method was used to analyze transition of strain-stress in soil samples. BSTEM is a fledged model for stability analysis of slope with plants. Effects of slope height, slope gradient, soil cohesion, internal friction angle, tree age and species on slope stability were studied with BSTEM.The major results were summarized as follow:(1) There were power function relations between basal diameter, main root, root biomass and diameter at breast height coordinate of horizontal roots of Pinus tabuleeformis and Robinia pseudoacacia. Root length and biomass were bigger in Robinia pseudoacacia than Pinus tabuleeformis. Both of the two species were deep-rooted plants while more proportion of Chinese pine roots was in deep soil compared with black locust.(2) There were power function relations between root maximum tensile force, tensile strength of Pinus tabuleeformis and root diameter. With root diameter increasing, maximum tensile force of Pinus tabuleeformis increased while tensile strength, elongation, elastic modulus decreased.(3) Tensile strength decreased with increased root length. A linear relation existed between them. Sampling time had no significant effect on root tensile strength. Two test speeds,10 mm/min and 400 mm/min, also had no significant effect. The order of tensile strength of five species was:Ulmus pumila L.> Betula platyphylla Suk.> Quercus mongolicus Fisch.> Pinus tabulaeformis Carr.> Larix principis-rupprechtii Mayr.(4) Triaxial compression tests verified roots can effectively improve soil shear strength. With increasing soil water content, soil cohesion decreased significantly. Triaxial compression test played an important role in evaluating soil reinforcement by roots. Combined triaxial compression test, finite element method could analyze well stress and strain variation in forested slope and root reinforcement.(5) When slope height and gradient increased, slope stability declined obviously. When soil cohesion increased, slope stability improved significantly. When soil internal friction angle added, minimum safety factor had indetectable change. Its effect could be ignored.