【作者】 刘艳；

【导师】 赵成刚；

【作者基本信息】 北京交通大学 ， 岩土工程， 2010， 博士

【摘要】 土力学发展到目前为止,其理论基础仍然很不完善,仍处于半理论、半经验的发展阶段,土力学统一和完备的理论基础仍有待于研究和发展。上世纪六七十年代发展起来的多相孔隙介质理论,为非饱和土力学的发展提供了理论基础。非饱和土是一种三相的多孔介质材料,它由固体颗粒和孔隙组成,孔隙中填充着水和气。气体的存在使得非饱和土的性质比饱和土要复杂得多,也使得影响非饱和土性质的因素变多,因此很难像饱和土那样找出非饱和土的响应(或应变)与应力状态之间的简单和唯一的关系。本文以多相孔隙介质力学理论为基础,提出了非饱和土广义有效应力原理,并建立了非饱和土的本构模型,主要研究成果为：(1)以多相孔隙介质理论为基础,从基本的物理规律即各种平衡方程出发,建立非饱和土的基本方程,并得到了非饱和土变形功的表达式。在总变形功的具体方程基础上提出了广义有效应力原理,给出了本文建议的与土骨架位移在功上对偶的有效应力表达式。指出应当选择非饱和土有效应力,修正吸力和气压三个应力状态变量来描述非饱和土的行为,并给出了相对应的功共轭的广义变形,为建立非饱和土本构方程奠定基础。(2)根据非饱和土的变形功表达式,推导得到了非饱和土各相的自由能和耗散势增量方程,然后采用热力学的方法来建立非饱和土的本构模型。根据广义有效应力原理选择应力变量,并选择适当的内变量来考虑非饱和土三相之间的联系,建立了固液气三相耦合的非饱和土本构模型框架。该框架将可以考虑很多复杂因素的影响,比如气相耗散对土体的影响等。(3)在非饱和土模型框架的基础上,通过适当的假设和简化,建立三轴应力状态下固液气三相耦合的非饱和土本构模型。其最大的特点在于首次在模型中考虑了气相硬化的影响,从理论的角度,这一模型由于考虑了气相压力变化的影响,因此更加全面和更具有一般性。采用已有的实验数据对模型进行验证,结果表明不论是在低饱和度阶段还是高饱和度阶段,模型都能很好的拟合试验结果。(4)对SFG模型进行了探讨和研究,指出其中存在的不足即无法考虑饱和度对土体性质的影响。以本文给出的有效应力为基础,提出了修正的SFG模型。该模型通过非饱和土的有效应力很自然地将SFG模型中无法考虑的饱和度对土体的影响引入进来。将修正后的模型与SFG模型进行了比较,并将模型与已有的试验数据进行了对比,结果表明本文模型在没有增加参数的同时可以考虑饱和度的影响并能反映更多的实验现象。更多还原

【Abstract】 So far the theory basis of soil mechanics is still far from consummate and still in a semi-theoretical, semi-empirical stage. It is necessary to develop a unified theoretical basis for soil mechanics. The multiphase porous medium theory, developed from 1960s, can describe the complex interaction in each phase and their response under external pressure or in complex environment, which provides a theoretical basis for soil mechanics. An unsaturated soil is a three phase porous media, consisting of soil skeleton and pores, with water and gas filled in the pores. The existence of gas in the soil makes its properties much more complex than saturated soils. Owing to the complexity of unsaturated soils, it is difficult to predict the deformation and strength behaviour of unsaturated soil uniquely. In this thesis, based on the multiphase porous media theory, the principle of generalized effective stress is derived, and the constitutive models of unsaturated soils can be further developed. The following conclusions can be drawn:(1) Based on the multiphase porous media theory and thermodynamics, the work and energy balance equations for unsaturated soils by using the geotechnical terminologies are derived. Then a principle of generalized effective stress for unsaturated soils is proposed, which makes preparation for constructing the constitutive models.(2) The free energy and the dissipation equation can be derived from the work expression. Based on the principle of generalized effective stress, the constitutive equations for unsaturated soils can be established using the thermomechanical method. The choice of internal state variables is important to build the relationship among the three phases. A solid-liquid-gas coupled constitutive modeling framework is established, which can consider many complex situations, for example the influence of gas dissipation on soil behaviour.(3) Based on the constitutive framework of unsaturated soils, a three phase coupled constitutive equations in triaxial stress state is presented with some reasonable assumption and simplification. The constitutive equations can be easy to apply in practice. The model is then used to predict the exiting experimental data, results showing the model agrees well with the test points in both low degree of saturation and high degree of saturation situation.(4) Studying on SFG model, it is found that the model could not consider the influence of degree of saturation on the soil behaviour. Using the principle of generalized effective stress deduced from the work expression, a modified model is proposed which can take the degree of saturation into account without increasing any more parameters. The modified model is then compared with SFG model, and model predictions are also given to simulate the existing experimental results.更多还原