林草混交根土复合体力学特性研究

发布时间：2018-06-05 12:06

本文选题：植物护坡 + 根土复合体　；参考：《中南林业科技大学》2014年硕士论文

【摘要】：边坡的失稳破坏是一种常见的、多发的自然地质灾害。我国南方多为丘陵地带,近20年来,高速公路、高速铁路等基础设施建设迅速发展,导致大量的路基边坡发生边坡失稳破坏。传统刚性边坡防护虽能大幅提高边坡稳定性,但造价高且严重破坏生态环境,而采用廉价的植被恢复技术进行生态护坡日益受到高度重视。种植草皮或根系较浅的植物等早期生态护坡方式只适于水土保持和浅层土体的防护,对于破裂面较大、较深的边坡效果不明显。采用工程技术和林草一体化的生态技术相结合的防护方法,在边坡上种植合适的灌木和草本植物,既可防护和控制表层滑坡,又可以对深层起到“植物土钉”的锚固作用。它不但可以提高坡体的整体稳定性,还可以消除噪音、改善公路周边的光、热环境和生态环境。因此,研究林草一体化高稳定性生态护坡技术,将边坡防护工程和生态效应进行有机结合,具有重要理论价值和工程意义。本文基于国内外生态边坡相关理论和先进技术,依托国家自然科学基金项目“高强度林草混交根系成型机理与边坡根系土体加固机制研究”(项目编号：31270671)、国家林业局948项目“林草一体化高稳定性生态护坡技术引进”(项目编号：2012-4-76)、湖南省自然科学基金资助项目“植物防护边坡力学特性研究”(项目编号：12JJ5015)、以及中南林业科技大学“研究生科技创新基金资助项目”(项目号：CX2012824)等开展相关研究。通过试验研究和理论分析,探讨了林草混交根土复合体的力学特性,研究工作的主要内容和取得的创新成果如下。研究工作的主要内容： 1、设计了不同的植株密度和边坡坡度,在室外模型箱内种植了草本植物香根草和灌木植物小叶女贞。 2、通过一年的培育后,对不同含根量、不同含根比和不同含水量等条件下的香根草和小叶女贞混交根系根土复合体进行了直剪试验,探索了在不同情况下混交根系根土复合体的抗剪强度规律。 3、对林草混交根系根土复合体进行了三轴剪切试验,进一步分析了混交根系根土复合体的抗剪强度特性。 4、在试验研究的基础上,通过模型分析和参数选择,对混交根系根土复合体的强度规律和本构模型等进行了理论研究。研究工作取得的主要创新成果： 1、草本植物香根草根系发达,根系直径一般为0.8-0.9mmm,80%的根系分布于距地表60cm深度以内。木本植物小叶女贞有明显主根,主根直径较大,竖直深入土壤深层,其侧根在地表中、上层生长繁密,且沿水平向延伸。 2、直剪试验研究结果表明,当土样中的含根量以及含根比一定时,在相同的竖向应力下,含水量越高,根土复合体的抗剪强度越低。且随着含水率的增加,无根土体和含根土体的抗剪强度均呈不同程度的降低,但含根土体的抗剪强度降低的程度较小。 3、当含水率一定,研究发现土壤粒径均匀程度和含根量对复合体的抗剪强度均有影响。相同含根量条件下,土壤粒径越均匀,根土复合体的抗剪强度越高；相同粒径条件下,植物根系含量越高,根土复合体的抗剪强度越高。 4、对草本或者木本植物根系根土复合体的抗剪强度采用二乘法进行拟合,其一次和二次拟合曲线均接近线性关系,表明草本或木本植物单一根系根土复合体的抗剪强度符合库伦强度理论。同样对林草混交根系根土复合体的抗剪强度进行一次和二次拟合,其一次二次拟合曲线均也均呈线性关系。因此,可以认为,林草混交根系根土复合体的抗剪强度亦符合库伦强度理论。 5、系列直剪试验表明,香根草和小叶女贞的根系均可明显提高根土复合体的抗剪强度。但二者对复合体抗剪强度指标的贡献是不同的,香根草系根的存在主要是提高了复合体的粘聚力,而小叶女贞系根的存在则主要提高了复合体的内摩擦角。 6、通过对根土复合体的内摩擦角与小叶女贞含根比进行非线性拟合,发现内摩擦角随小叶女贞含根比的增大而呈幂函数形式增长,从而建立了根土复合体的内摩擦角与小叶女贞含根比的幂函数关系式,且幂函数的系数是与含水率和含根量相关的常数。 7、通过对林草混交根土复合体进行三轴剪试验研究,得到了不同围压条件下林草混交根土复合体的应力-应变曲线。通过分析复合体的应力-应变曲线发现,在不同围压下,偏应力和轴向应变之间均较好地符合双曲线关系,且轴向应变-偏应力之比与轴向应变之间具有较好的线性关系,符合邓肯张模型特点。基于邓肯张模型,本文建立了邓肯张E-B模型形式的林草混交根系根土复合体的本构模型,并提出了新模型参数的具体确定方法。以上研究为探索林草混交根土复合体的力学特性,开发并应用高稳定性的林草护坡技术,具有重要的理论价值和广阔的工程应用前景。
[Abstract]:The instability failure of the slope is a common and multiple natural geological hazard. In the south of China, the hilly area is mostly in the south. In the past 20 years, the construction of the basic facilities, such as highway and high speed railway, has developed rapidly, causing a large number of roadbed slopes to be unstable and unstable. Although the traditional rigid slope protection can greatly improve the stability of the slope, the cost is high and strict. The ecological environment is seriously damaged, and the ecological slope protection is paid more and more attention by the cheap vegetation restoration technology. The early ecological slope protection methods such as planting grass skin or the shallow roots are only suitable for soil and water conservation and shallow soil protection. For the larger fracture surface and the deeper slope, the integration of engineering technology and forest grass integration is not obvious. The protection method combined with ecological technology, planting suitable shrubs and herbaceous plants on the slope, not only protects and controls the surface landslides, but also plays the role of anchoring the "plant soil nailing" in the deep layer. It can not only improve the stability of the slope, but also eliminate the noise sound, improve the light, thermal environment and the ecological environment around the highway. Therefore, it is of great theoretical value and engineering significance to study the high stability ecological slope protection technology of forest grass integration and to combine the slope protection engineering with the ecological effect.
Based on the domestic and foreign ecological slope theory and advanced technology, relying on the National Natural Science Foundation Project "high strength forest and grass mixed root forming mechanism and the soil reinforcement mechanism of slope root system" (project number: 31270671), the national forestry bureau 948 project "integration of forest grass integration and high stability ecological slope protection technology introduction" (project compilation) 2012-4-76), Hunan Natural Science Fund funded project "study on mechanical characteristics of plant protection slope" (project number: 12JJ5015), and Central South University of Forestry and Technology "graduate science and technology innovation fund funded project" (project number: CX2012824) to carry out related research. Through experimental research and theoretical analysis, the mixed forest and grass were discussed. The main contents and achievements of the research work are as follows.
The main contents of the research work are as follows:
1, we designed different plant density and slope gradient, and planted herbaceous vetiver and shrubs in the outdoor model box.
2, after one year of cultivation, a direct shear test was carried out on root soil complex of root soil of vetiver and Ligustrum Lucidum with different root content, different root ratio and different water content, and the shear strength of root soil complex of mixed root system under different conditions was explored.
3, three axis shear tests were conducted on the root soil complex of mixed forest and grass, and the shear strength characteristics of the root soil complex of mixed roots were further analyzed.
4, based on the experimental research, the strength law and constitutive model of the root soil complex of mixed roots were studied theoretically through the model analysis and parameter selection.
The main innovative achievements of the research work:
1, the root system of herb root is developed, the root diameter is generally 0.8-0.9mmm, and the root of 80% is distributed within the depth of the surface 60cm. Ligustrum lucidum has obvious main root, the main root diameter is larger, the root is deep deep in the soil, its lateral roots are in the surface, the upper layer grows dense and extends horizontally.
2, the results of direct shear test show that the shear strength of root soil composite is lower when the content of root and the ratio of root ratio is certain, the higher the water content is, the lower the shear strength of the root soil complex is under the same vertical stress. The shear strength of the root soil and the root soil decreases with the increase of water content, but the shear strength of the soil containing the root soil decreases. The degree is small.
3, when the water content is certain, it is found that the soil particle size uniformity and the root content have influence on the shear strength of the complex. Under the same root content, the more uniform the soil particle size is, the higher the shear strength of the root soil complex, the higher the plant root content, the higher the shear strength of the root soil complex.
4, the shear strength of root soil complex of herbaceous or woody plants was fitted with two multiplications, and the first and two fitting curves were close to linear relation, indicating that the shear strength of the root soil complex of herbaceous or woody plants accorded with the Kulun strength theory. The two fitting curves of the one and two times are all linear. Therefore, it is considered that the shear strength of the mixed root soil complex of the mixed forest grass is also in line with the Kulun strength theory.
5, a series of direct shear tests showed that the roots of vetiver and Ligustrum lucidum could obviously improve the shear strength of the rhizosphere complex. But the contribution of the two to the shear strength index of the complex was different, and the existence of the root of vetiver was mainly enhanced by the cohesion of the complex, while the existence of the Ligustrum virginity was mainly improved in the complex. Angle of friction.
6, through the nonlinear fitting of the internal friction angle of the root soil complex and the root ratio of Ligustrum lucidum, it is found that the internal friction angle increases with the increase of the root ratio of Ligustrum lucidum, and establishes a power function relation between the internal friction angle of the root soil complex and the ratio of the root of Ligustrum lucidum, and the coefficient of power function is with water content and content. The constant of the root quantity.
7, the stress strain curve of the mixed root soil complex under different confining pressure was obtained by the three axial shear test of the mixed root soil complex of the forest and grass. The stress strain curve of the composite was found by the analysis of the stress strain curve of the complex. The relationship between the partial stress and the axial strain was better under the different confining pressure. There is a good linear relationship between the stress ratio and the axial strain, which conforms to the characteristics of the Duncan tension model. Based on the Duncan tension model, this paper establishes the constitutive model of the root soil complex of the mixed roots and grass roots in the form of Duncan Zhang E-B model, and puts forward a specific method for determining the parameters of the new model.
In order to explore the mechanical properties of the mixed root soil complex of forest and grass, the development and application of high stability forest grass slope protection technology has important theoretical value and broad engineering application prospects.
【学位授予单位】：中南林业科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU43

【参考文献】