Improvement of Nondestructive Structure Imaging for Rock by X-ray Computed Tomography

x射线计算机断层扫描是一种非破坏性成像技术，它可以通过从不同方向拍摄的阴影图像的数字化和随后的图像重建来评估材料中每个点的x射线衰减。将该技术应用于土工材料，提出了改进的软件和实验技术，用于岩石中流体运移、土壤中污渍定位、岩石内部裂缝张开剖面等图像处理。在流体运移方面，提出了一种简单的岩石盘片渗流实验方法来测量渗透系数，并提出了序列图像相减和局部平均技术，以及实验结果的解释理论。针对土壤和砂土中的斑点定位问题，新提出了利用CT值的局部偏差来评价碎片化机制，并对三维序列图像进行相应的平滑和灰度阈值处理。针对球形空腔和盘状空腔等空腔周围的裂缝显示，明确了将放大与透视图相结合的方法，可以有效地研究裂缝扩展机理。针对岩石和混凝土内部的裂缝开度分布，提出了一种基于图像减法和区域平均技术的裂缝投影法。

X-ray Computed Tomography is a nondestructive imaging technique, which makes it possible to evaluate the attenuation of X-ray at each point within materials, by digitizing shadow pictures taken from various directions and subsequent image reconstruction. This technique was applied to geo-materials, and the improved software and experimental technique were presented for the image processing of the fluid migration in rock, the stain localization in soil, the crack opening profile within rock and so on.In regard to the fluid migration, a simple percolation experiment using a disc specimen of rock was proposed to measure the coefficient of permeability, along with the subtraction of serial images and the local region averaging technique, and the theory for interpreting the experimental results. With respect to the stain localization in soil and sand, the local deviation of CT values was newly utilized to evaluate the fragmentation mechanism, together with the pertinent smoothing and the subsequent grey-level thresholding of three dimensional serial images. With regard to the visualization of fracture around the cavity such a spherical cavity and a disc-shaped cavity, the combination of zooming and perspective drawing was clarified to be effective for the investigation of fracture propagation mechanism. In regard to the crack opening profile within rock and concrete, a new scheme named the Crack Projection Method was presented to evaluate the aperture distribution along crack by means of the image subtraction and the regional averaging technique.