关键词: 冻融, CT扫描成像技术, 伪彩色增强, 扫描电镜, 显著性分析

Abstract: The grain-size formation in water/soil science is solely based on the soil characteristics (moisture and minerals) which ultimately determine the sizes of soil grains considering their interactions and surrounding environment. In this study, a methodology was utilized using different approaches (detailed observation, microscopic and macroscopic measurements) to determine loess evolution through time that affected its grain formation and structure. To explore the effect of freeze-thaw damage scale structure of loess environment, the loess Huangling county of Yanan city was taken as the research object with the initial moisture content and the number of freeze-thaw cycles as variables. Through the apparent structure test of scanning electron microscope and CT scanning, with variations of the loess body rate and freeze-thaw cycles, fine structure view and macro features in different initial water contents were explored. Based on Leica Qwin, Canny operator edge detection, fractal dimension, rainbow code pseudo color enhancement technology and saliency theory, the experimental results were analyzed. Testing results showed that with the increase of the number of freeze-thaw cycles, micro structure significantly changed. Specific changes include: particle size becomes uniform, skeleton connection mode changes, surface to surface contact mode changes to point to surface and point to point contact modes, and connection between grains weakens. Microscopic view showed a decrease of high density region and an increase of low density region, and an increase of the frost heaving force. Migration force continues to appear, enabling reduction of the loess body integrity and development of migration channel, which causes increase of ice volume from macro analysis . With the increase of the number of freeze-thaw cycles, surface porosity and fractal dimension increase in the beginning and become stable after 10 cycles. Under freeze-thaw environment, internal micro pores continue to transform into large pores. Enhanced dye technology significantly improves the recognition of CT image. The factors causing alteration of loess grain structure are not only the initial water content and the number of freeze-thaw cycles, but also the interaction (coupling) between water content and freeze-thaw cycles, which has a significant effect on grain structural alteration.

Key words: freeze-thaw cycles, CT scanning imaging technique, pseudo color enhancement, scanning electron microscopy, significance analysis