A numerical method for analyzing the permeability of heterogeneous geomaterials based on digital image processing

Abstract

In this study, we propose a digital image processing technology for estimating the macro permeability property of heterogeneous geomaterials. The technology is based on a connected-component labeling algorithm and provides a novel and effective method for geometry vectorization and microstructure identification. A color photo of a soil and rock mixture (SRM) is taken as an example. Information about the distribution of aggregate and a vectorgraph, which can be used in numerical analysis, are obtained automatically. A numerical permeability test is carried out to estimate the macro permeability coefficient of the heterogeneous medium. The effects on macro permeability of three parameters, scale dependency, material heterogeneity and the rock fraction, are discussed. The results indicate that the SRM has a scale dependent property and the representative element volume (REV) length is about six times the maximum major axis of the aggregate. The heterogeneity parameter has a major effect on macro permeability characteristics within a certain range. There is a weak tendency for the macro permeability to decrease as the rock fraction increases. Although the rock fraction is not the only factor, it does have an influence on the macro permeability. We conclude that the novel method developed in this study has good prospects for widespread application in macro parameter estimation and related research fields.

摘要

目的

建立一种较为快速和快速确定非均匀岩土材料渗 透系数的方法。

创新点

建立了一种可以从图像到数值模型的数字图像方 法:通过拍照、CT 等手段获取岩土材料的图像, 进而通过数值分析确定等效参数。

方法

1. 将采集到彩色图像从RGB 空间转化到HSI 空 间,选取识别度较高的空间进行二值化处理; 2. 获取二值化图像后采用邻域标记算法标记,结 合本文提出的算法提取边界(图9 和10);3. 结 合边界修正算法对锯齿状边界进行修正(图11); 4. 确定表征细观几何模型(图12 和表1);5. 绘 制网格开展数值分析,确定宏观参数。

结论

1. 基于数值图像的非均匀岩土材料渗透系数确定 方法可以较为准确地估算渗透系数,可以为工程 设计提供初步依据。2. 非均匀岩土材料具有明显 的尺寸效应,随着尺寸增加,渗透率的变化逐渐 趋于稳定;当材料视为岩石和土体的二元介质 时,两种性质差异在10 倍以内对宏观特性的影 响较大,大于10 倍之后影响减弱。3. 岩土材料 渗透率随着内部块石含量的增加而减小,但是内 部块石的形态对渗透率也有一定的影响。