| 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. |
