【作者】 李舰；

【导师】 赵成刚；

【作者基本信息】 北京交通大学 ， 岩土工程， 2014， 博士

【摘要】 摘要：膨胀土区域中的边坡防护、渠道开挖、建筑物基础的不均匀沉降等岩土工程和高放废物地下处置工程中都涉及到膨胀性非饱和土在外荷载和含水量变化作用下的变形、强度、渗流、持水等问题。膨胀土作为一种特殊的土的类型,其行为较为复杂,产生的机理亦异于一般的非饱和土。目前膨胀土的理论很不完善,需要进一步的研究和发展。本文的研究对象,即膨胀性非饱和土不同于一般的非饱和土。一方面,原状粘土、较低含水量的压实粘土以及由膨润土粒状体组成的土体等膨胀性非饱和土均具有明显的双孔隙结构特征。另一方面,由于膨胀土中含有蒙脱石和伊利石等强亲水性矿物,因此土中固相基质与附近液相间的物理-化学作用明显,表现出宏观的湿化膨胀的特性,并且液相的性质随孔隙的尺寸和其在孔隙中的位置的不同而变化。上述两方面导致膨胀非饱和土的力学和水力行为较一般的非饱和土的行为更加复杂。所以,需要针对膨胀性非饱和土的双孔隙结构和其膨胀性的特点,发展和完善已有的非饱和土力学的理论,并为进一步的工程应用奠定基础。本文针对具有双孔隙结构的膨胀性非饱和土进行了系统的研究,取得了以下主要研究成果：(1)基于多相孔隙介质理论和基本的物理定律,针对膨胀性非饱和土结构的特殊性,推导得到具有严格理论基础的膨胀性非饱和土外力输入功的表达式。在上述推导过程中,区分了土体内部的宏观孔隙和微观孔隙,以及孔隙中的毛细液相和吸附液相。因此,依据功的表达式可以选取多组功共轭的变量作为进一步构筑本构模型的广义应力和广义应变的变量。其中包括描述宏观和微观变形以及不同尺度的孔隙中液相含量变化的变量等。(2)基于膨胀性非饱和土输入功的表达式以及开放的多相热力学系统中能量-功-耗散之间的关系,建立适用于具有多尺度孔隙结构特征的非饱和土的本构模型理论框架。并且基于该理论框架,通过一些合理的假设和简化,在等向压力条件下建立了双尺度的水力滞回-力学耦合模型。文中首先根据以往研究者常采用的假设条件对上述推导而得的土体输入功的表达式进行了简化。简化后的输入功包含3项,分别为宏观孔隙变形所对应的功,宏观孔隙中毛细液相饱和度变化所对应的功,以及微观结构变化所对应的功。推导过程中,通过选取合适的内变量反映功的表达式中3项间的联系。所建立的双尺度的水力滞回.力学耦合模型可同时考虑力学和水力行为间的耦合作用,以及土中微观结构的变化对土体整体行为的影响。(3)建立了一个适用于膨胀性非饱和土的二元介质模型,模型中考虑基质吸力中的毛细部分和粘吸部分对膨胀土行为的不同作用和影响。以往研究中,研究者们常忽略基质吸力中粘吸部分。然而就膨胀土而言,土中固相基质与其附近液相间的物理-化学作用显著,既粘吸部分的作用不容忽视。文中根据二元介质模型的建模方法,将膨胀性非饱和土抽象为由两个理想部分组成,即理想毛细部分和理想粘吸部分,并且分别建立适用于这两者的本构关系。然后利用参与函数,反映实际情况下理想毛细部分和理想粘吸部分所占据或参与的比重。文中仿照二元介质模型的建模思路,提出了一种在已有的非饱和土本构模型的基础上,考虑土中固相基质和附近液相间的物理-化学作用,即基质吸力中粘吸部分的作用和影响的非饱和土本构模型。(4)基于热力学中储存塑性功的概念,对干湿循环路径下膨胀土的变形行为产生的机理进行了探讨和研究。并建立了适用于基质吸力循环路径下的膨胀性非饱和土的本构模型。文中指出由于膨胀土中集聚体的易延展性和颗粒间的相互制约作用,使得土中集聚体内存在一定的储存塑性功。因此,可将基质吸力循环引起的膨胀土的塑性变形分为两部分,其中一部分由颗粒间的重排列引起,另一部分由土中集聚体内储存的塑性能量的增加引起。为了反映上述特征,文中利用混合硬化准则建立了相应的弹塑性本构模型。更多还原

【Abstract】 ABSTRACT:In expansive soil layer, projects of underground high-level radioactive waste disposal and geotechnical engineering, such as slope protection, channel excavation, uneven settlement of building foundation and etc., involve the deformation, strength, seepage and retention water behaviors of expansive unsaturated soil. As the object of study in this thesis, unsaturated expansive soils are other than low and moderate plasticity unsaturated soils. Many unsaturated expansive soils, such as natural and compacted clays and bentonite pellet mixtures, have a pore size distribution with at least two dominant values of porosity. Furthermore, the physiochemical effect between the solid matrix and adjacent water are obvious. Thus the property of pore water changes with pore size and location. The above two reasons lead to more complex mechanical and hydraulic behaviors of unsaturated expansive soil than that of the unsaturated soil. Thus, in terms of its specific characteristics of structure and deformation, there is a need to develop and improve the existing theory of unsaturated soil, which could also lay a theoretical foundation for engineering application.The paper mainly contains the following parts:(1) Based on the porous media theory and the essential laws of physics, the input work of unsaturated expansive soils are proposed. In the process of derivation, the pores are classified into macro-and micropores, meanwhile, the pore water is classified into capillary water and adsorbed water. Then several pairs of energy-conjugate variables could be determined, e.g. the macro-and microstructural strains, the macrostructural degree of saturations of capillary water and adsorbed water, the microstructural degree of saturation and their energy-conjugate stress variables.(2) According to the derived input work expression of unsaturated expansive soils and the work-energy-dissipation relations for an open multiphase thermodynamic system, a thermodynamics-based modelling framework for unsaturated expansive soils with double porosity is established. Based on the thermodynamics-based modelling framework, a double-scale constitutive model for isotropic stress state is proposed, involving coupling of hydraulic hysteresis and mechanical behaviors. The input work expression is simplified based on the some common hypothesis. There are three terms in the simplified expression, i.e. the work caused by the macrostructural deformation, the work caused by the change of macrostructural degree of saturation, the work caused by the change of microstructure. In the derivation process of the thermodynamics-based modelling framework, the internal variable is used to couple the three terms. The proposed model takes two factors into consideration:the interaction between the micro-and macro-structure of expansive soils and the fully coupled capillary hysteresis with mechanical behaviors.(3) A new binary-medium model for unsaturated expansive soils is proposed, involving a consideration of the effects of the capillary component and the adsorptive component of matric suction on the behaviors of unsaturated expansive soils. Most constitutive models for unsaturated soils are proposed on the basis of the capillarity mechanism, ignoring the contributions of the adsorption effect to mechanical and hydraulic behaviors. For expansive clays, however, the adsorption effect which leads to more complex behavioral characteristics than that in low plasticity clays cannot be ignored. The expansive clay is assumed as a mixture of two parts, i.e. an ideal capillarity part and an ideal adsorption part, and two ideal constitutive models are established for the ideal parts, respectively. Then a participation function is used to reflect the proportions of the ideal capillarity part and the ideal adsorption part in the actual situation. According to the thought of establishing the disturbed models, a method dealing with the physicochemical effect, i.e. the adsorptive component of matric suction, is proposed, which is extended by the existing unsaturated soil model based on the capillarity mechanism.(4) On the basis of the thermodynamics concept of stored energy, the mechanisms of the deformation behaviors of unsaturated expansive soils under suction cycles paths are discussed. Moreover, a new constitutive model for unsaturated expansive soil is proposed. The generation of the stored energy for soils is attributed to the deformability of the individual aggregate and mutual restrictions among the adjacent aggregates. By means of analysis, the plastic deformation can be decomposed into two parts, which are attributed to the structural rearrangements and the change of stored plastic work, respectively. And then the combined isotropic-kinematic hardening rule is used to consider the mechanism of plastic deformation. The proposed model can quantitatively predict the behaviour of unsaturated expansive soils under suction cycles.更多还原