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

X射线计算机层析成像是一种无损成像技术，它通过数字化从不同方向拍摄的阴影图像和随后的图像重建来评估材料内每个点的X射线衰减。将该技术应用于岩土材料中，提出了改进的软件和实验技术，用于岩石中流体运移、土体应变局部化、岩石中裂隙张开轮廓等的图像处理；对于流体运移，提出了一种利用岩石圆盘试件测量渗透系数的简单渗流实验，并结合序列图像减法和局部区域平均技术，给出了解释实验结果的理论依据。对于土壤和沙子中的污渍定位，新的方法是利用CT值的局部偏差来评价碎裂机理，并对三维序列图像进行适当的平滑和随后的灰度阈值处理。对于球形空腔和盘形空腔周围裂缝的可视化，提出了变焦和透视图相结合的方法，可以有效地研究裂缝扩展机理。针对岩石和混凝土中的裂缝张开轮廓，提出了一种新的方法--裂缝投影法，利用图像减法和区域平均技术来估算裂缝中的孔洞分布。

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.