【作者】 况联飞；

【导师】 周国庆；

【作者基本信息】 中国矿业大学 ， 岩土工程， 2013， 博士

【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。更多还原

【Abstract】 Insight into the high stress mechanical properties of saturated clay is of greatimportance in the fields of deep mine construction and nuclear waster disposalengineering, and these properties have been revealed in general in the past, but not thegoverning mechanisms. On the other hand, the structure of clay presents inmulti-scale, which means that the description of its properties from a single scale willbe unilateral. So in this dissertation, by employing computer simulations andtheoretical analysis, a systematic studies are conducted to investigate the basicmechanisms of high stress mechanical properties for saturated montmorillonite.First, we investigate the microstructure and nano-scale mechanical properties forhydrated Na-, Ca-and Cs-montmorillonite under ambient and basin condition bymolecular dynamic simulation.The simulation results show that the bonding degree of the interlayer water issignificantly higher than free water, and ion hydration coordination is also remarkablyhigher than corresponding bulk case. By further examine the characteristics of boundwater under basin condition, we find that there is almost no difference for thestructure of bound water between basin and ambient condition within2km burialdepth, and the main affecting factor is temperature. On these basis, we quantitative getthe stiffness matrix of hydration montmorillonite together, the tensile and compressivestrength perpendicular to the clay lamellae is significantly lower than the in planeatom bond strength, showing a clear anisotropy. And interlayer bound water has shearstrength to some degree, which is governed by its high viscosity.Second, mesoscopic structure and mechanical response of hydratedmontmorillonite are simulated by means of dissipative particle dynamics simulation.The interaction parameters of the mesoscopic model are estimated by mapping thecorresponding no bonded energy values obtained from atomistic molecular dynamicsimulations, and the mesoscopic simulation results show that the water structure isslightly different from free water for the78.4%water content montmorillonite system,but its diffusion coefficient and viscosity parameter indicate that under this conditionthe interlay water performance mainly as free water, and the mesoscopic K0compression simulation reveals that with the vertical strain increasing, the verticalstress increases non-liner parabolic, while the lateral stress increases linear, therebymaking the mesoscopic K0nonlinear. Third, By taking into account the short-range hydration repulsion, we modify thetraditional Gouy-Chapman diffusion double layer theory and analysis the high stresscompressibility of saturated clay by this new theory in macroscopic.This new theory is modified by additional considering the dielectric saturation andion volume exclusion effects, compared to the others model the calculated dielectriccoefficient between particle plates changes more smoother, and the potential valueunder small plates spacing is higher than the tradition double layer theory, whichmeans that the short-range hydration repulsion plays a role. In addition, thequantitative calculation result of van der Waals shows that the attraction betweenplates should be taken into account under high stress compression. Then, wecomprehensive calculate the repulsion and attraction forces between particle platesand get the theory compressive curve for saturated under high stress. Finally, thefactors that affect the high stress compressibility are analysised together.Finally, based on the micro-and meso-simulations and macroscopic theory results,we comprehensive analysis the basic mechanisms that govern the high stresscompression and shear mechanical properties for saturated montmorillonite.The theory results show that the bilinear characteristic of high stress compressioncurves for initially saturated montmorillonite can be reproduced well by the modifiedtheory, and the interlayer bound water will only partially dehydrated under thecondition of maximum overburden pressure of40MPa. Further, the correspondingplates distance for interlayer water characteristic changing from free water to boundwater can be got for mesoscopic and microscopic molecular simulation, and thepressure range that calculated from the macroscopic theory corresponding with theseplate spacings are in good agreement with test turning pressure. Which revealed thatunder high stress compression the plate distance for montmorillonite particle willcompress into basic crystal spacing, and the water characteristic will change from freewater to bound water, that the partially dehydrated of bound water govern the basicmechanism of high stress compression for saturated montmorillonite, and thedifference between various compensative cation montmorillonite lies in the differenceof ion hydration ability. And there is transformation process form mineral friction tointerlayer water shear with the stress increasing, which controls the basic mechanismof high shear.更多还原