含随机裂纹网络孔隙材料的渗透性研究

发布时间：2018-02-08 14:27

本文关键词： 孔隙材料渗透性裂纹网络连通度逾渗　出处：《清华大学》2015年博士论文　论文类型：学位论文

【摘要】：孔隙材料在力学荷载和环境因素作用下会产生裂纹。裂纹产生、扩展和连通对材料的渗透性影响显著,进而影响材料的使用性能。本文通过理论分析、数值模拟和试验研究对含随机裂纹网络孔隙材料的渗透性进行了系统研究。本文首先基于连续区逾渗理论并考虑裂纹网络的分形特征提出了有限区域内裂纹网络的连通度定义。然后在含裂纹夹杂的相互作用直推(IDD)理论模型基础上,引入裂纹网络的连通度和裂纹的开度信息,定义与连通度相关的水平裂纹密度,按照增量法将表征连通特征的水平裂纹嵌入有效基体中,以此方式来考虑裂纹夹杂间的相互作用,提出了考虑裂纹连通特征的扩展IDD模型。随后开展了含裂纹网络孔隙材料渗透率逾渗模型的研究,采用裂纹面密度作为逾渗基本变量,计算了不同裂纹网络的逾渗阈值以及阈值附近的标度指数;考虑裂纹网络的连通度和主裂纹团的曲折度给出了渗透率标度律的解析解,分别考虑了裂纹网络的几何逾渗特征、孔隙材料渗透率以及裂纹开度比。以水泥基孔隙材料为研究对象,研究了裂纹网络对材料渗透率和电导率等传输性质的影响。为了沿试件厚度方向得到上下表面一致的二维裂纹网络,本文采用人工制造裂纹再拼接的方法得到不同开裂程度的薄片试件。对开裂试件表面的二维裂纹形貌特征进行了定量分析,包括裂纹的密度、取向、裂纹开度、连通度等。测试了普通混凝土和砂浆材料的等温吸附与脱附曲线,得到两种材料的水分特征曲线。然后尝试使用水分迁移的多相流模型来模拟试件的干燥过程,同时对比干燥实验中不同开裂程度试件的质量变化过程来回归其对应的本征渗透率。最后给出裂纹网络不同的形貌参数对渗透率和电导率的影响。研究表明:(1)通过裂纹网络几何分析可知,随机裂纹局部团簇效应会降低裂纹网络的整体连通性,数值结果验证了连通度定义方法的合理性;(2)从数值的角度分别验证了不连通和部分连通裂纹网络扩展IDD模型的适用性;(3)当裂纹的局部渗透率与基体渗透率比值高于106后,裂纹开度对渗透率不再有影响;(4)当裂纹密度大于临界阈值0.3时,渗透率和电导率增加迅速。渗透率与裂纹开度成指数关系,指数接近2.0,而电导率与裂纹开度大致呈线性关系。由于试验研究在二维裂纹网络上进行,利用试验结果可以检验之前建立数值和理论模型的准确性。
[Abstract]:Cracks will occur in porous materials under mechanical loads and environmental factors. Crack generation, propagation and connectivity have a significant effect on the permeability of the material, and then affect the performance of the material. The permeability of porous materials with random crack networks is studied by numerical simulation and experimental research. Firstly, based on the continuous percolation theory and considering the fractal characteristics of crack networks, a finite area crack network is proposed. Then based on the IDD model of interaction with crack inclusions, By introducing the connectivity and crack opening information of the crack network, the horizontal crack density related to the connectivity is defined, and the horizontal crack representing the connectivity characteristic is embedded in the effective matrix according to the incremental method. In this way, the interaction between crack inclusions is considered, and a propagating IDD model considering crack connectivity is proposed. Then, the permeability percolation model of porous materials with cracks is studied, and the crack surface density is used as the basic percolation variable. The percolation threshold and scale exponent near the threshold value of different crack networks are calculated, the analytical solution of permeability scaling law is given considering the connectivity of crack networks and the twists of main crack clusters, and the geometric percolation characteristics of crack networks are considered, respectively. Permeability and crack opening ratio of porous materials. The effect of crack network on the permeability and conductivity of materials is studied. In order to obtain a two-dimensional crack network with consistent upper and lower surfaces along the thickness of the specimen, In this paper, a method of artificial crack reassembly is used to obtain thin specimens with different cracking degrees. The two-dimensional crack morphology of the cracked specimen surface is quantitatively analyzed, including crack density, orientation, crack opening, etc. The isothermal adsorption and desorption curves of ordinary concrete and mortar materials were measured, and the water characteristic curves of the two materials were obtained. Then the multi-phase flow model of water migration was used to simulate the drying process of the specimens. At the same time, the corresponding intrinsic permeability was regressed by comparing the mass variation process of specimens with different cracking degree in drying experiment. Finally, the effects of different morphology parameters of crack network on permeability and conductivity were given. Geometric analysis of cracked network shows that, The global connectivity of crack networks can be reduced by the local cluster effect of random cracks. The numerical results verify the rationality of the connectivity definition method. (2) from a numerical point of view, the applicability of the IDD model for the propagation of disconnected and partially connected crack networks is verified respectively.) when the ratio of local permeability to matrix permeability of the crack is higher than 10 6, the applicability of the IDD model is verified respectively. When the crack density is greater than the critical threshold 0.3, the permeability and conductivity increase rapidly, and the permeability is exponentially related to the crack opening. The exponent is close to 2.0, and the conductivity is approximately linear with the crack opening. Since the experimental study is carried out on a two-dimensional crack network, the accuracy of the numerical and theoretical models established before the experiment can be verified by using the experimental results.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU52

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