A comparison study of pore structure and permeability of sandstone by BSE-SE images

The pore structure and permeability of geotechnical materials are critical parameters that guide underground engineering. With advancements in digital imaging technology, scanning electron microscopy (SEM) has emerged as a vital tool for examining the pore structure and permeability of these materials. SEM operates in two primary modes: backscattered electron imaging (BSE) and secondary electron imaging (SE), each of which emphasizes different aspects of the material's structure. However, few studies have been conducted to elucidate the influence of these two modes on the quantification of geotechnical structural characteristics. This study undertakes a more comprehensive quantitative analysis of the structure and permeability of sandstones by juxtaposing the two modes. The findings indicate that the BSE mode excels in analyzing the structure and composition, whereas the SE mode highlights the surface morphology. In terms of image segmentation, BSE mode images are more conducive to effective segmentation. Although SE images permit viable segmentation when preprocessed, they tend to represent a greater number of discrete tiny pores. Furthermore, there exists a discernible correlation between pore size and shape, wherein larger pores exhibit heightened roughness and deviate more from sphericity. Notably, these larger pores predominantly contribute to the material's permeability. Given that the BSE mode more readily captures continuous pore structures, the permeability values derived from BSE images are significantly higher than those obtained from SE images. These findings hold profound implications for enhancing our comprehension of geotechnical materials' pore structure and permeability, thereby informing the strategic use of BSE and SE modes in related studies.