饱和蒙脱土高压力学特性基本机制多尺度研究

发布时间：2018-06-15 21:42

本文选题：蒙脱土 + 力学特性　；参考：《中国矿业大学》2013年博士论文

【摘要】：深部矿井建设及深地质核废料埋藏工程对饱和粘土在高压条件下的力学特性研究提出了新的要求，已有研究成果对该特性进行了表观披露，但未就其控制机理作出合理解释。同时，粘土结构的多阶性决定了从单一尺度条件下对其特性进行描述将存在偏缺。为此，本文围绕饱和粘土（蒙脱土）高压力学特性的基本机制展开了微观、介观和宏观多尺度层面上的系统研究。首先，采用分子动力学方法对钠、钙和铯三种水化蒙脱石体系在常温常压以及埋深温压条件下的微观结构和力学特性进行了模拟。模拟定量刻画出了土中结合水的原子分子层次上的赋存状态和活动特性，结果显示结合水的聚合程度明显高于自由水，同时离子的水化配位也要大于相应的体相溶液数值，且不同离子间差异明显。进一步考察埋深温压条件下的结合水特性得出，2km埋深条件下层间结合水的结构与常温常压差别很小，且其主要影响因素为温度。在此基础上，模拟还定量获得了水化蒙脱石体系的刚度矩阵，其纳观力学特性表现为垂直矿物平面方向上的拉压强度明显低于矿物平面内的成键连结强度，呈明显的各向异性。同时，层间结合水具有一定的抗剪强度，进一步的剪切模拟则揭露出该抗剪强度发挥的根源在于结合水的粘度远远高于自由水溶液。该系列的研究全面给出了结合水的最底层面描述，同时不同离子的水化差异揭露为宏观不同粘土的高压力学特性差异解释奠定了基础。其次，采用耗散粒子动力学手段对水化蒙脱石体系在实际单一晶片物理尺度条件下的介观结构和力学响应进行了模拟。通过非键结合能实现了微观分子模拟与介观尺度的递阶关联，同时增大蒙脱石珠子数目并作固壁冻结处理的策略使得耗散粒子动力学模拟在土-水体系中得到了首次成功应用。介观模拟结果表明，78.4%含水量蒙脱石中水的结构虽略异于自由水，但其扩散系数和粘度活动性参数均表明该条件下的水主要表现为自由水特性。而介观K0压缩模拟则得出，随着垂直矿物平面应变的增大，竖向应力呈非线性抛物线增大，侧向应力则为线性增大，由此使得介观K0非线性。再次，基于水化斥力考虑，改进了传统扩散双电层理论并对饱和粘土的高压压缩特性进行了宏观理论分析。改进理论考虑了介电饱和及离子体积排斥效应，其计算获得的颗粒板间介电系数变化较其他模型均更为光滑合理，且小间距条件下的板间电势要高于传统双电层理论，即对应为短程水化斥力的发挥。而对范德华力的定量计算结果则得出高压压缩必须考虑板间引力作用。为此，综合引、斥力定量计算结果获得了粘土高压压缩理论e~logP曲线，同时一并分析其压缩性的各因素影响。最后，基于微、介观模拟及宏观理论对饱和蒙脱土高压压缩和剪切的基本机制进行了综合分析。结果显示附加考虑水化斥力的改进理论能够很好地描述饱和蒙脱土高压压缩的双折线试验结果，其定量计算数值得出40MPa压力范围内蒙脱土层间将部分脱水，但又不至于完全脱附。而基于微观分子模拟和介观模拟获得了自由水向结合水转化的板间距对应数值，进一步按宏观理论得到的该板间距范围内的压力大小与试验e~logP曲线拐弯压力能够很好地吻合，从而揭露出饱和蒙脱土高压压缩的颗粒板间距将朝基本晶层距发展，排出水的特性将由自由水向结合水过渡，也即控制饱和蒙脱土高压压缩的基本机制在于土中结合水的部分脱附，，而不同离子蒙脱土的高压压缩性差异则在于离子的水化能不同。而对于高压剪切的基本机制则认为随着压力的增大存在矿物间摩擦向层间结合水抗剪转化的过程，并据此解释了深土高压直剪测定的内摩擦角在高压条件下要小于低压约9左右的试验事实。
[Abstract]:Deep mine construction and deep geological nuclear waste buried engineering put forward new requirements for the study of the mechanical properties of saturated clay under high pressure. The existing research results reveal the characteristics of this characteristic, but do not make a reasonable explanation of its control mechanism. At the same time, the multi order of clay structure determines its characteristics under the condition of single scale. In this paper, the basic mechanism of the high pressure mechanical properties of saturated clay (montmorillonite) has been studied in this paper on the microcosmic, mesoscopic and macro multiscale systems.
First, the microstructure and mechanical properties of three kinds of montmorillonite systems with sodium, calcium and cesium were simulated by molecular dynamics method under the conditions of atmospheric pressure and buried depth.
The result shows that the degree of aggregation of the combined water is obviously higher than that of the free water, and the hydration coordination of the ions is also greater than that of the corresponding body phase solution, and the difference between the different ions is obvious. It is found that the structure of interlayer water in 2km buried depth is very small, and the main influence factor is temperature. On the basis of this, the stiffness matrix of the hydrated montmorillonite system is obtained, and the tensile strength of the vertical mineral plane is obviously lower than that in the mineral plane. The bond strength is obviously anisotropic. At the same time, the interlayer binding water has a certain shear strength. Further shear simulation reveals that the root of the shear strength is that the viscosity of the combined water is much higher than that of the free water solution. The study of the series gives a comprehensive description of the bottom layer of the combined water and the water of different ions. The differential disclosure lays a foundation for the differential interpretation of the high-pressure mechanical properties of macroscopic clay.
Secondly, the mesoscopic structure and mechanical response of the hydrated montmorillonite system under the actual single chip physical scale were simulated by the dissipative particle dynamics method.
The hierarchical correlation between micromolecular simulation and mesoscopic scale is realized by non bond bonding, and the strategy of increasing the number of montmorillonite beads and making the solid wall freezing treatment makes the dissipative particle dynamics simulation used in the soil water system for the first time. The mesoscopic simulation results show that the structure of water in 78.4% water content montmorillonite is slightly different. In free water, the diffusion coefficient and viscosity activity parameters show that the water is mainly free water under this condition, while the mesoscopic K0 compression simulation shows that the vertical stress increases with the increase of the plane strain of the vertical mineral, and the lateral stress increases linearly, which makes the mesoscopic K0 nonlinear.
Thirdly, based on the consideration of hydration repulsion, the traditional diffusion double layer theory is improved and the high pressure compression characteristics of saturated clay are theoretically analyzed.
The effect of dielectric saturation and ion volume rejection is considered in the improvement theory. The change of the dielectric coefficient between the plates is more smooth and reasonable than that of the other models, and the interplate potential under the small spacing is higher than the traditional double layer theory, that is, it corresponds to the short-range hydrated repulsion. The results of the quantitative calculation for Vander Ed Ley are obtained. The gravitational force between plates must be considered for high pressure compression. For this reason, the e~logP curve of the high pressure compression theory of clay is obtained by the comprehensive introduction and the repulsive force quantitative calculation results. At the same time, the influence of various factors on the compressibility of the clay is analyzed.
Finally, the basic mechanism of high pressure compression and shear of saturated montmorillonite is comprehensively analyzed based on micro mesoscopic simulation and macroscopic theory.
The results show that the improved theory of the additional consideration of the hydration repulsion can well describe the results of the double fold line test of the high pressure compression of saturated montmorillonite. The quantitative calculation results show that the 40MPa pressure range will be partially dehydrated between the dehydrated layers of Inner Mongolia, but it is not completely desorbed. Based on the micromolecular simulation and mesoscopic simulation, the free water direction is obtained. The plate spacing of the water is corresponded to the numerical value. The pressure size within the range of the plate spacing in the macro theory is in good agreement with the bending pressure of the test e~logP curve. Thus it is revealed that the spacing of the particle plate in the high pressure compression of the saturated montmorillonite will develop towards the basic crystal spacing, and the characteristics of the discharged water will be transition from free water to the combined water. The basic mechanism of high pressure compression of saturated montmorillonite lies in the partial desorption of water in the soil, while the high pressure compressibility of different ion montmorillonite lies in the different hydration energy of the ions.
For the basic mechanism of high pressure shear, it is believed that with the increase of pressure, there is a process of shear transformation between interlayer friction and interlayer water with the increase of pressure. According to this, the experimental fact that the internal friction angle of the deep soil high pressure direct shear is less than about 9 under the high pressure condition is explained.
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU43

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