粒径及级配特性对土体渗透系数影响的细观模拟

Microscopic simulation of influence of particle size and gradation on permeability coefficient of soil

渗透系数是体现土体渗透特性的主要参数。已有关于粒径及级配特性对土体渗透系数影响的研究主要采用试验研究方法,在试验研究中各个变量相互影响,很难完全独立改变某一参数,从而造成已有研究结论差异较大。在其他参数不变条件下数值模拟基本可以独立改变某一参量,弥补试验研究方法的不足。采用离散元数值模拟方法,通过调节控制粒径的方式,随机生成不同粒径、不同孔隙率、不同级配的土体多孔介质。利用格子Boltzmann方法从细观孔隙流体尺度模拟了土中的渗流。研究结果表明,格子Boltzmann方法可以准确有效地模拟土中的渗流;在渗流过程中存在主通道现象和大粒径效应;计算结果与Kozeny-Carman(简称K-C)公式完全一致,且证明K-C公式适用于不同级配的土体;渗透系数随不均匀系数和曲率系数的增大而增大;给出了一个包含级配参数的渗透系数计算公式,该公式与K-C公式基本等价,但所含参数是工程中较易测量的,对实际工程有一定的参考意义。

Permeability coefficient is a main parameter to reflect the permeability of soil. Existent studies about influence of particle size and gradation on permeability coefficient of soil mainly focused on experiments. It is difficult to change a parameter completely independently because of the interaction of various variables in the experimental study, which results in considerable differences between the conclusions from different researchers. Under the condition that other parameters remain unchanged, numerical simulation can basically change a certain parameter independently to make up for the shortcomings of experimental methods. In this paper, the particle discrete element method is used to generate soil of porous media with different particle sizes, different porosities and gradations by adjusting the size of the control particles. Lattice Boltzmann method is used to simulate seepage in soil at meso-pore fluid scale. The results show that the lattice Boltzmann method can simulate soil seepage accurately and effectively. Main passageway phenomena and large particle size effect are found in the seepage process. The simulation results are in good agreement with those by Kozeny-Carman(K-C) formula, demonstrating the K-C formula is applicable to porous media with different gradations. The permeability coefficient increases with the increase of uniformity coefficient and the curvature coefficient. A formula for calculating permeability coefficient with gradation parameters is given. The formula is nearly equivalent to K-C formula, but the parameters in this formula can be measured easily.