饱和砂土基于相变状态的循环本构模型的研究

发布时间：2019-04-25 23:12

【摘要】：迄今为止,针对饱和砂土的研究表明,剪胀、循环和各向异性是其力学特征中三个重要的特性,也是区别于其它材料明显不同的地方。而饱和砂土的应力应变曲线中均出现一个特殊状态的点,即相变点,该状态点对饱和砂土上述三个特征具有特殊意义。因此本文从上述三个方面,对饱和砂土在单调和循环荷载作用下的力学反应,做进一步的研究。本文在已有饱和砂土本构模型的基础上,从砂土的微观机理出发,考虑剪胀过程中组构变化对累积塑性应变的影响,并考虑饱和砂土的循环作用,建立基于相变状态的循环边界面模型,描述不同的排水条件下,单调和循环荷载作用下砂土的力学行为。本文的主要研究成果为：1、首先通过不同荷载作用下饱和砂土试验现象的探讨,从砂土的微观现象出发,讨论砂土微观结构变化引起的宏观变形的机理,进而用宏观的变量反映微观颗粒间的变化；引入组构-剪胀内变量,用以反映反向加载过程中,微观组构引起的宏观剪胀张量的变化对循环荷载作用下,饱和砂土塑性累积变形的影响,并建立宏观与微观之间的联系。2、纵观已有砂土的循环本构模型,其塑性模量的确定一般都比较繁琐,并且涉及的参数也较多。本文直接从试验现象出发,针对排水情况下,饱和密砂在循环荷载作用下体积的变化越来越小的现象,总结出首次加载与再加载过程中(即单调与循环加卸载过程中)塑性模量的变化规律,并对已有的塑形模量表达式进行了修正,提出易于确定、适合循环加载的塑性模量的表达式。3、针对1993年Ishihara提出的e-log p'表达式,结合张卫华提出的状态参量的表达式,揭示了此关系式模拟饱和砂土在不排水条件下的力学行为时存在不足。本文对其加以改进,提出适合不排水条件计算相变孑隙ept的表达式,并建立不排水单调本构模型。通过试验数据对本构模型和所提出的相变孔隙比ept。的表达式分别进行了验证,结果表明本构模型能较好地反映不排水过程中有效应力的变化,并且相变孔隙比ept的表达式也是合理和有效的。4、综合上述三点工作,针对循环荷载(不包括动荷载)作用,进一步提出饱和砂土不同排水条件下的循环边界面本构模型。模型描述了不同排水条件下循环荷载作用下的力学行为,如排水条件下饱和砂土先剪缩后剪胀的变形过程,及循环过程中体变增量越来越小并最后趋于稳定的变化趋势；不排水条件下的有效应力变化及应力应变间的关系。同样,模型也能较好地反映出不同排水条件下砂土的相变点和峰值点。
[Abstract]:Up to now, the study of saturated sand shows that shear expansion, cycling and anisotropy are three important mechanical characteristics of saturated sand, which are also different from other materials. There is a special point in the stress-strain curve of saturated sandy soil, that is, phase transition point, which is of special significance to the above-mentioned three characteristics of saturated sandy soil. Therefore, in this paper, the mechanical response of saturated sand under monotonic and cyclic loads is further studied from the above three aspects. Based on the existing constitutive model of saturated sand and the microscopic mechanism of sand, the influence of fabric change on accumulated plastic strain in the process of shear expansion is considered, and the cyclic action of saturated sand is also considered in this paper. A cyclic boundary interface model based on phase transition is established to describe the mechanical behavior of sand under monotonic and cyclic loads under different drainage conditions. The main research results of this paper are as follows: 1. Firstly, through the discussion of saturated sand test under different loads, the mechanism of macro-deformation caused by the change of microstructure of sand soil is discussed from the micro-phenomenon of sand soil, and the mechanism of macro-deformation caused by the change of micro-structure of sand soil is discussed. Then the macro-variables are used to reflect the change of micro-particles. The fabric-shear expansion internal variable is introduced to reflect the influence of micro-fabric-induced macro-shear expansion Zhang Liang on plastic cumulative deformation of saturated sand under cyclic loading. The relationship between macro and micro is established. 2. Generally, the determination of plastic modulus of the existing cyclic constitutive model of sand is cumbersome and involves a lot of parameters. In this paper, the change of volume of saturated dense sand under cyclic load is getting smaller and smaller under the condition of drainage from the point of view of experimental phenomenon. The variation rule of plastic modulus in the process of first loading and reloading (that is, monotone and cyclic loading and unloading) is summarized, and the existing formula of plastic modulus is modified, which is easy to determine, and it is easy to determine the plastic modulus in the process of first loading and reloading. Expression of plastic modulus suitable for cyclic loading. 3. According to the expression of e-log p 'proposed by Ishihara in 1993, combined with the expression of state parameter proposed by Zhang Weihua, It is revealed that this equation has some shortcomings in simulating the mechanical behavior of saturated sand under undrained conditions. In this paper, an expression for calculating phase transition relict ept suitable for undrained conditions is put forward, and a monotone constitutive model for undrained is established. Study on Constitutive Model and proposed Phase change porosity ept. based on Experimental data The results show that the constitutive model can better reflect the change of effective stress in the undrained process, and the expression of phase transition porosity ratio ept is also reasonable and effective. According to the cyclic load (excluding dynamic load), the constitutive model of cyclic boundary of saturated sand under different drainage conditions is proposed. The model describes the mechanical behavior of saturated sand under cyclic loading under different drainage conditions, such as the deformation process of saturated sand at first shearing and then dilating, and the trend that the volume increment becomes smaller and tends to be stable at last. The relationship between effective stress change and stress-strain under undrained condition. At the same time, the model can well reflect the phase transition point and peak point of sand under different drainage 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】：2015
【分类号】：TU441

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