本文選題：蒙脫土 + 力學特性　； 參考：《中國礦業(yè)大學》2013年博士論文

【摘要】：深部礦井建設(shè)及深地質(zhì)核廢料埋藏工程對飽和粘土在高壓條件下的力學特性研究提出了新的要求，已有研究成果對該特性進行了表觀披露，但未就其控制機理作出合理解釋。同時，粘土結(jié)構(gòu)的多階性決定了從單一尺度條件下對其特性進行描述將存在偏缺。為此，本文圍繞飽和粘土（蒙脫土）高壓力學特性的基本機制展開了微觀、介觀和宏觀多尺度層面上的系統(tǒng)研究。 首先，采用分子動力學方法對鈉、鈣和銫三種水化蒙脫石體系在常溫常壓以及埋深溫壓條件下的微觀結(jié)構(gòu)和力學特性進行了模擬。 模擬定量刻畫出了土中結(jié)合水的原子分子層次上的賦存狀態(tài)和活動特性，結(jié)果顯示結(jié)合水的聚合程度明顯高于自由水，同時離子的水化配位也要大于相應(yīng)的體相溶液數(shù)值，且不同離子間差異明顯。進一步考察埋深溫壓條件下的結(jié)合水特性得出，2km埋深條件下層間結(jié)合水的結(jié)構(gòu)與常溫常壓差別很小，且其主要影響因素為溫度。在此基礎(chǔ)上，模擬還定量獲得了水化蒙脫石體系的剛度矩陣，其納觀力學特性表現(xiàn)為垂直礦物平面方向上的拉壓強度明顯低于礦物平面內(nèi)的成鍵連結(jié)強度，呈明顯的各向異性。同時，層間結(jié)合水具有一定的抗剪強度，進一步的剪切模擬則揭露出該抗剪強度發(fā)揮的根源在于結(jié)合水的粘度遠遠高于自由水溶液。該系列的研究全面給出了結(jié)合水的最底層面描述，同時不同離子的水化差異揭露為宏觀不同粘土的高壓力學特性差異解釋奠定了基礎(chǔ)。 其次，采用耗散粒子動力學手段對水化蒙脫石體系在實際單一晶片物理尺度條件下的介觀結(jié)構(gòu)和力學響應(yīng)進行了模擬。 通過非鍵結(jié)合能實現(xiàn)了微觀分子模擬與介觀尺度的遞階關(guān)聯(lián)，同時增大蒙脫石珠子數(shù)目并作固壁凍結(jié)處理的策略使得耗散粒子動力學模擬在土-水體系中得到了首次成功應(yīng)用。介觀模擬結(jié)果表明，78.4%含水量蒙脫石中水的結(jié)構(gòu)雖略異于自由水，但其擴散系數(shù)和粘度活動性參數(shù)均表明該條件下的水主要表現(xiàn)為自由水特性。而介觀K0壓縮模擬則得出，隨著垂直礦物平面應(yīng)變的增大，豎向應(yīng)力呈非線性拋物線增大，側(cè)向應(yīng)力則為線性增大，由此使得介觀K0非線性。 再次，基于水化斥力考慮，改進了傳統(tǒng)擴散雙電層理論并對飽和粘土的高壓壓縮特性進行了宏觀理論分析。 改進理論考慮了介電飽和及離子體積排斥效應(yīng)，其計算獲得的顆粒板間介電系數(shù)變化較其他模型均更為光滑合理，且小間距條件下的板間電勢要高于傳統(tǒng)雙電層理論，即對應(yīng)為短程水化斥力的發(fā)揮。而對范德華力的定量計算結(jié)果則得出高壓壓縮必須考慮板間引力作用。為此，綜合引、斥力定量計算結(jié)果獲得了粘土高壓壓縮理論e~logP曲線，同時一并分析其壓縮性的各因素影響。 最后，基于微、介觀模擬及宏觀理論對飽和蒙脫土高壓壓縮和剪切的基本機制進行了綜合分析。 結(jié)果顯示附加考慮水化斥力的改進理論能夠很好地描述飽和蒙脫土高壓壓縮的雙折線試驗結(jié)果，其定量計算數(shù)值得出40MPa壓力范圍內(nèi)蒙脫土層間將部分脫水，但又不至于完全脫附。而基于微觀分子模擬和介觀模擬獲得了自由水向結(jié)合水轉(zhuǎn)化的板間距對應(yīng)數(shù)值，進一步按宏觀理論得到的該板間距范圍內(nèi)的壓力大小與試驗e~logP曲線拐彎壓力能夠很好地吻合，從而揭露出飽和蒙脫土高壓壓縮的顆粒板間距將朝基本晶層距發(fā)展，排出水的特性將由自由水向結(jié)合水過渡，也即控制飽和蒙脫土高壓壓縮的基本機制在于土中結(jié)合水的部分脫附，，而不同離子蒙脫土的高壓壓縮性差異則在于離子的水化能不同。 而對于高壓剪切的基本機制則認為隨著壓力的增大存在礦物間摩擦向?qū)娱g結(jié)合水抗剪轉(zhuǎn)化的過程，并據(jù)此解釋了深土高壓直剪測定的內(nèi)摩擦角在高壓條件下要小于低壓約9左右的試驗事實。
[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.
【學位授予單位】：中國礦業(yè)大學
【學位級別】：博士
【學位授予年份】：2013
【分類號】：TU43

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