护坡灌木根—土力学作用时间尺度效应研究

发布时间：2018-02-10 04:55

本文关键词： 植被护坡根系抗拔边坡浅层稳定性分形 ABAQUS　出处：《西南交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：植被护坡技术虽然在国内已获得广泛的应用,但植被护坡工程的长期稳定性,尤其是工程运营期力学稳定性仍然备受质疑,现有的研究成果对此也未能给出很好的解答。总体来看,针对植被护坡技术的长期有效性研究,还远远不够。鉴于此,本文对护坡灌木根系与土体之间相互作用力学机理从时间尺度展开研究,通过理论推导、室内试验及数值模拟方面分析了植被边坡长期稳定性、灌木根系抗拔能力的影响因素以及灌木形态对边坡稳定性的影响,取得了主要成果有:(1)在总结前人研究成果的基础上,指出灌木粗根是逐渐生长的活生物体,并不等同于一般工程锚杆,具有明显的时间效应;将其假设成全长粘结型锚杆未考虑抗拔能力随时间变化的动态过程;(2)分析了灌木根系在径向生长时整株抗拔力的增加情况;对此建立力学模型,推导出基于灌木深根径向生长的锚固力公式;并将计算结果与已有文献现场试验结果进行比较,证实了抗拔力与时间呈幂函数关系。(3)对根系与边坡相互作用的力学模型进行论述,讨论基于根系纵向生长时力学模型的适用性,探究不同锚固深度情况下稳定安全系数计算方法;运用公式对某工程实例进行计算,计算结果显示边坡的稳定性持续提升,与实地观察结果相符,证实模型合理,为植被边坡长期有效性提供了理论依据;(4)室内正交试验结果表明,侧根数量是影响根系竖向抗拔力的最主要因素,对根系的竖向抗拔能力影响最大,其次是主根长度、根周围土体重度,侧根分枝角度对抗拔力影响最小。从力学角度看,发达的根系更有利于边坡浅层稳定,从时间尺度看,根系生长过程中不断分蘖出侧根,加固效果会越来越好。(5)灌木根系的形态有明显的的时间效应。随着时间推移,根系的分形维数随之改变;根系的形态越复杂,分形维数越大。灌木根系能有效控制边坡浅层变形,使得边坡由"脆性破坏"转"延性破坏",浅层稳定性得到提高。植被灌木根系分形维数越大,边坡的安全系数越大,最大塑性应变越小;拟合结果显示安全系数增幅与根系的计盒维数呈幂函数关系,最大塑性应变减幅与之呈线性关系。
[Abstract]:Although vegetation slope protection technology has been widely used in China, the long-term stability of vegetation slope protection projects, especially the mechanical stability of engineering operation period, is still questioned. In general, the long-term effectiveness of vegetation slope protection technology is far from enough. In this paper, the mechanism of interaction between shrub roots and soil is studied from time scale. The long-term stability of vegetation slope is analyzed by theoretical derivation, laboratory test and numerical simulation. The influence factors of shrub root resistance and the influence of shrub morphology on slope stability have been obtained. On the basis of summing up the previous research results, it is pointed out that shrub thick root is a living organism growing gradually. It is not equal to the general engineering anchor, and has obvious time effect, and it is assumed that the full-length bonded anchor does not take into account the dynamic process of the change of pull-out ability with time.) the increase of the whole plant's pullout resistance of the shrub root system in radial growth is analyzed. A mechanical model is established, and the anchoring force formula based on the radial growth of deep roots of shrubs is derived, and the calculated results are compared with the results of field tests. It is proved that the relationship between pull-out force and time is a power function. The mechanical model of the interaction between root system and slope is discussed, and the applicability of the mechanical model based on the longitudinal growth of root system is discussed. This paper probes into the calculation method of stability safety factor under different anchoring depth, and calculates a project example by using the formula. The calculation results show that the stability of the slope continues to improve, which is consistent with the field observation results, and proves that the model is reasonable. The results of laboratory orthogonal experiments show that the number of lateral roots is the most important factor affecting the vertical pullout resistance of root system, and the main root length is the second. The soil around the root was heavy and the lateral root branching angle had the least influence on the pull-out force. From the mechanical point of view, the developed root system was more conducive to the stability of the shallow layer of the slope. From the time scale, the lateral root was continuously tilled out during the root growth. The morphology of shrub root system has obvious time effect. The fractal dimension of root system changes with time; the more complex the root form, the more complex the root system is. The larger the fractal dimension is, the more the shrub root system can effectively control the shallow deformation of the slope, which makes the slope change from "brittle failure" to "ductile failure", and the shallow stability is improved. The larger the fractal dimension of the vegetation shrub root is, the greater the safety factor of the slope is. The maximum plastic strain is smaller, and the fitting results show that the increase of safety factor is power function with the box-counting dimension of root system, and the maximum plastic strain decreasing amplitude is linear with it.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：Q948;TU43

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