基于状态参量的饱和砂土弹塑性本构模型研究

发布时间：2018-08-11 10:17

【摘要】：饱和砂土在静力和动力荷载作用下,具有压硬性、剪胀性、应变硬化和应变软化等特点。考虑状态参数的影响,研究饱和密砂和中密砂土在剪应力作用下的变形特性,建立饱和砂土的弹塑性模型已经是近年来国际岩土工程界的重要研究领域和研究方向,具有重要的学术价值和实践意义。本论文在国内外大量试验结果的基础上,以北京市自然科学基金资助项目(8112024)、北京市教委科技发展计划项目(KM200910009008)为依托,对饱和密实和中密砂土在静力荷载作用下的变形特点和剪胀规律开展了系统和深入的研究工作。取得的主要研究成果如下： (1)论述了密实砂土和中密砂土剪胀性的特点和影响剪胀的因素。通过对已有试验结果的分析和整理,考虑密实砂土和中密砂土体变过程的特点,提出应关注这类砂土的相转换临界状态点,简称为相变点。并进一步指出相变点是这类砂土变形过程的一个关键状态。诸多试验表明,在相变孔隙比和相变围压构成的平面上,二者呈直线关系,也即相变线方程是线性变化的。因此,本文建立了呈线性变化特征的相变线方程或数学表达式。并以相变线作为参照标准,以相变孔隙比为具体参照量,提出了新的状态参量表达式和新的剪胀比计算公式。这一状态参量综合考虑了应力水平和材料状态的影响。结合相变孔隙比和临界状态孔隙比,利用状态参量的概念可以较为准确地判断砂土在初始时和任意时刻的剪胀趋势。以此为基础建立的砂土的弹塑性模型即可以较真实地反映土的体积先剪缩后剪胀的变化全过程和变形特性。 (2)对于砂土,其剪胀比不能被视为应力比的唯一性函数,这一点与黏性土不同。因为砂土的剪胀比不仅与三轴应力变量q和p'有关,而且还与材料的内部状态有关,即土的密实程度有关。在颗粒破碎前,按照这一思路建立砂土的剪胀性模型可以突破以往的一些障碍,以契符合土体受力和变形的实际情况。本文建立的剪胀比计算公式,考虑了材料状态的影响,把具有不同密度的同一类砂处理为一种砂而不是两种砂,可以较好地描述剪缩和剪胀两种体积变化过程。 (3)本文基于前面建立的饱和砂土的考虑状态参量影响的剪胀比计算公式,实现和达到了考虑材料状态对剪胀比影响的目标。在此基础上,提出了一种能真实地反映密实砂土和中密砂土体积变化过程的砂土弹塑性本构模型,仅用一组模型参数即可以描述同一种砂土在不同初始密度和不同围压条件下的应力应变特性。 (4)进行了系列饱和砂土实验。通过与各种初始状态和加载条件下砂土相应的实验数据的比较,证明该模型具有较好的模拟能力。
[Abstract]:Saturated sand under static and dynamic loads has the characteristics of compression hardness, dilatancy, strain hardening and strain softening. Considering the influence of state parameters, it is important to study the deformation characteristics of saturated sand and medium-dense sand under shear stress and to establish the elastic-plastic model of saturated sand. On the basis of a large number of experimental results at home and abroad, the deformation of saturated and medium-dense sands under static loads is studied in this paper, which is supported by the Beijing Natural Science Foundation (8112024) and the Beijing Education Commission's Science and Technology Development Program (KM200910009008). The characteristics and dilatancy laws have been studied systematically and thoroughly.
(1) The characteristics of dilatancy and the factors affecting dilatancy of compacted sand and medium-dense sand are discussed. Based on the analysis and collation of the existing experimental results and considering the characteristics of deformation process of compacted sand and medium-dense sand, the critical state point of phase transition of this kind of sand is proposed, which is called phase transition point for short. A key state in the deformation process. Many experiments have shown that there is a linear relationship between the phase change pore ratio and the phase change confining pressure on the plane formed by the phase change pore ratio and the phase change pore ratio. A new expression of state parameter and a new formula for calculating dilatancy ratio are proposed for concrete reference. The state parameter takes into account the effects of stress level and material state. Combining phase change void ratio and critical state void ratio, the concept of state parameter can be used to judge the dilatancy of sand at the beginning and at any time accurately. The elastic-plastic model of sandy soil based on this model can truly reflect the whole process and deformation characteristics of soil volume change after shear dilatancy.
(2) For sands, the dilatancy ratio can not be regarded as the unique function of the stress ratio, which is different from clay because the dilatancy ratio of sands is not only related to the triaxial stress variables Q and p', but also to the internal state of the material, i.e. the compactness of the soil. The formulas for calculating the dilatancy ratio are established in this paper. Considering the influence of material state, the same kind of sand with different densities is treated as one kind of sand instead of two kinds of sand, which can better describe the volumetric variations of shear shrinkage and dilatancy.
(3) Based on the formulas for calculating the dilatancy ratio of saturated sands considering the influence of state parameters, this paper achieves and achieves the goal of considering the influence of material state on the dilatancy ratio. On this basis, a sand elastic-plastic constitutive model which can truly reflect the volumetric variation process of compacted sands and medium-dense sands is proposed. The model parameters can describe the stress-strain characteristics of the same sand under different initial density and confining pressure.
(4) A series of saturated sand experiments are carried out. The model is proved to have good simulation ability by comparing with the corresponding experimental data of sand under various initial conditions and loading conditions.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU441

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