Rock and Soil Mechanics ›› 2022, Vol. 43 ›› Issue (8): 2103-2114.doi: 10.16285/j.rsm.2021.6726

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Multi-scale analysis of damage evolution of freezing-thawing red sandstones

ZHANG Hui-mei, WANG Yun-fei   

  1. Department of Mechanics, Xi'an University of Science and Technology, Xi’an, Shaanxi 710054, China
  • Online:2022-09-30 Published:2022-09-30
  • About author:ZHANG Hui-mei, female, born in 1968, PhD, Professor, PhD supervisor, mainly engaged in the teaching and research work of theoretical analysis and engineering application of rock freeze-thaw damage in cold regions.
  • Supported by:
    the National Natural Science Foundation of China (12172280, 42077274, 41907259) and the Key Program of Natural Science Foundation of Shaanxi (2020JZ-53).

Abstract: We take red sandstone as the research object and apply the freeze-thaw cycles, CT scans and mechanical properties experiments. We use image processing technology combined with genetic algorithm optimization model to achieve the denoise, enhancement, segmentation and three-dimensional reconstruction of CT scan images after 0, 5, 10, 20, and 40 freeze-thaw cycles. With the damage identification and comparative study of the same object across scales, we established a prediction formula of elastic modulus deterioration based on mesoscopic damage. Therefore, the macroscopic mechanical behavior of freeze-thaw red sandstones can be interpreted from the physical nature of the material meso-structure. The results show that genetic algorithm based on image maximum entropy can quickly and accurately select the threshold for image segmentation, and achieve the recognition of matrix and defects in rock meso-structure. With the increase of freezing and thawing cycles, the porosity of rock increases, and the fractal dimension of pore decreases. On the meso-scale, the evolution shows that the pores expand and the number increases, but the structural complexity decreases. The macroscopic and mesoscopic damage variables defined by the traditional methods are based on the effective bearing area and elastic modulus, and they fail to fully consider the damage physical mechanism and the internal structure information of the material. The damage evolution curves are different. Based on the two physical mechanisms, we define the meso-damage variable and the macro-damage variable that considers the natural rock damage, which achieves the combination of macroscopic and mesoscopic damages. Finally, according to the relationship between meso-structure evolution and macroscopic mechanical response in the process of freeze-thaw cycles, we propose a prediction formula of elastic modulus degradation, and analyze the different dominant roles of pore size and pore structure morphology through the damage process. We interpret the mechanical mechanism of macroscopic sandstone freeze-thaw damage based on the meso-structure physical mechanisms.

Key words: freeze-thaw sandstone, damage, multi-scale, physical mechanism, macro-meso combination