基于SEM多级化孔隙特征研究——以重塑黄土为例

SEM-BASED MULTI-LEVEL PORE CHARACTERISTICS-A CASE STUDY OF REMOLDED LOESS

为了探究扫描电镜(SEM)下多尺度微观孔隙特征,确定孔隙定量分析的最佳放大倍数,利用IPP 6.0软件对12种不同放大倍数(包括100X、200X、300X、400X、500X、600X、800X、1000X、1200X、1500X、2000X、3000X)下8个不同干密度的重塑黄土试样的SEM图像进行孔隙多级化分析,并依据雷祥义的黄土孔隙分类标准对孔隙进行统计分类。结果表明:在放大倍数小于400X时,任何干密度试样的SEM图像都无法观察到微孔隙,在放大倍数大于1000X时,无法观察到大孔隙,而在放大倍数介于400~1000X时,基本可以观察到不同类型的孔隙;基于多元统计学中的聚类分析,得到放大倍数的分类结果与IPP 6.0软件对SEM图像的处理统计结果相一致;不同干密度试样多级化孔隙特征的差异主要是由土体密实度变化使得不同孔隙类型转化而引起的;随着放大倍数的增大,视域变小,大孔隙越难统计;反之,放大倍数越小,视域越大,微孔隙越容易被忽略;在综合考虑微孔隙和大孔隙的分布及其含量下,最佳观察倍数应介于500~800X之间。该研究不仅有助于揭示重塑黄土基于SEM多级化孔隙特征,同时对地质工程领域土体微结构定量表征具有借鉴价值。

This paper explores the characteristics of micro pores at multi-scale using the scanning electron microscope(SEM)and determines the best magnification for quantitative analysis of pores.It analyses the SEM images of remolded loess samples with eight dry densities at 1,2 different magnifications(100X,200X,300X,400X,500X,600X,800X,1000X,1,200X,1500X,2000X,3000X)with IPP 6.0 software.It statistically classifies the loess pores according to Lei Xiangyi s classification standard.The results show the follows.When the magnification is less than 400X,the micropores can not be observed in any SEM image,and the macropores can not be observed at the magnification greater than 1000X.However,four different types of pores can be basically observed when the magnification is between 400X and 1000X.Based on the cluster analysis,the classification results of magnification are consistent with the statistical results of SEM images processed with IPP 6.0 software.The difference in multi-scale pore characteristics of samples with eight dry densities is mainly due to the transformation of different pore types with the change of soil compactness.With the increase of magnification,the field of view becomes narrower and the macropores are more difficult to be counted.On the contrary,the smaller the magnification is,the larger the visual field is,and the more easily the micropores are to be ignored.Considering the distribution and content of micropores and macropores,the best observation multiple is between 500X and 800X.This study not only helps to reveal the pore characteristics of remolded loess at multi-scale based on SEM,but also has reference value for quantitative characterization of soil microstructure in the field of geological engineering.