基于电镜成像原理的黏土微结构参数提取方法

Extraction method for micro-structure parameters of clay based on imaging principles of scanning electron microscope

土体受静、动力作用发生变形的过程必然伴随着微观结构的变化。土体微结构变化的定量化描述是宏微观土力学中非常重要且具有挑战性的内容。提出了一种基于电镜扫描原理、从扫描图像中提取黏土微观结构局部几何信息的方法。首先基于电镜扫描过程中成像二次电子的产生数量、不同逸出方向的电子流强度基本原理和描述方程,从理论上建立了"高亮—阴影"过渡区电镜扫描图像的灰度与上、下两搭接黏土片的相对倾角、间距等局部黏土片排列几何参数间的理论关系。随后将该方法用于真实扫描图像分析,成功提取出成对黏土片的间距和相对倾角,理论预测的遮挡因子—距离关系与实测关系规律一致,证明了该方法的可行性;理论上,该方法受电镜扫描图像中常见的欠"曝光"、过"曝光"、随机噪声缺陷影响较小。

Soil deformation under static or dynamic loads is accompanied by adjustment of its microscopic structure.It is an essential and challenging task to quantitatively describe the micro-structure evolutions of soil for micro-to-macro geomechanics.This study proposes a method to extract information of relative arrangement of clay plates from scanning electron microscope(SEM)images based on the physical principles of SEM imaging techniques.First,a theoretical relationship between the grey scale of SEM images in the high-contrast transition zone(with very high and very low grey scales)and the local geometric quantity describing the clay plate arrangement is derived.This relationship considers the laws and functions about the generation rate and angular intensity distribution of the secondary electrons.The local geometric quantities include inclinations of the scanned clay plates and the distance between the two neighboring clay plates.Then,the proposed method is validated by applying it to the analysis of a real SEM image.The distance and relative inclination of two neighboring clay plates are successfully extracted.The relationship between the shadow factor and the distance predicted theoretically by this method and that obtained from the real SEM image are consistent,validating the correctness and capability of the proposed method.Theoretically,the proposed method is not sensitive to the defects in the SEM image such as overexposure,underexposure and random noise.