Abstract
The mesostructures of rocks determine their macromechanical properties. These rock mesostructures may be altered by the freeze-thaw cycles in cold regions. In this regard, this paper proposes a quantitative evaluation method based on computed tomography (CT) scanning technology for investigating the mesostructure and damage characteristics of sandstone subjected to freeze-thaw conditions. CT scan images of two sandstones with different grain sizes were obtained after 0, 20, 40, 60, 80, and 100 freeze-thaw cycles, using a high-precision CT scanner. Based on the microphysical information contained in these CT images, pseudo-color-enhancement of the CT images of rocks subjected to freeze-thaw cycles was realized. The use of such a pseudo-color-enhancement technique can improve the resolution of CT images. Thus, particle detachment, crack initiation, crack propagation, and increased porosity due to the volumetric expansion of water inside the rock could be detected and clearly observed. Furthermore, a numerical expression for the mesostructure and damage information contained in the pseudo-color-enhanced images is presented herein; this serves as a convenient method for quantitative analyses of sandstone damage under freeze-thaw cycles. An analysis of the pseudo-color-enhanced images shows that, under freeze-thaw cycles, damage propagation in sandstone originates from existing damage or defect sites. After the stages of crack (pore) formation, penetration, and propagation, the freeze-thaw cycle-induced damage increases gradually, while the effective bearing area of the rock decreases continuously. Herein, a schematic of a conceptual model for the freeze-thaw cycle-induced deterioration in sandstone mesostructures is presented. Damage propagation models for sandstones with two different grain sizes subjected to freeze-thaw cycles were also developed. Based on the damage mechanics theory, a damage variable expressed in terms of the pore area was defined. Moreover, the relationship between this damage variable and the freeze-thaw cycles was established.
Highlights
In the cold western regions of China, for the construction of infrastructure and the development of mineral resources, porous sandstone such as the Permian Shihezi Formation, quartz-cemented sandstone such as the Shanxi Formation, and argillaceous cemented sandstone such as the Jurassic Zhiluo Formation are widely employed. ese form one of the principal aquifers in engineering geology
For a quantitative investigation of the mesodamage characteristics of sandstones subjected to freeze-thaw cycles using computed tomography (CT) techniques, this study proposes a CT image processing method based on CT scanning and an image enhancement technique (CT-IET)
Pseudo-color-enhancement of the CT images indicates the degradation of the mesostructures due to the damage caused by different freeze-thaw cycles. us, the entire change in the rock mesostructures could be analyzed, including the particle detachment, crack initiation and propagation, and increased porosity caused by the volumetric expansion of water inside the rock
Summary
In the cold western regions of China, for the construction of infrastructure and the development of mineral resources, porous sandstone such as the Permian Shihezi Formation, quartz-cemented sandstone such as the Shanxi Formation, and argillaceous cemented sandstone such as the Jurassic Zhiluo Formation are widely employed. ese form one of the principal aquifers in engineering geology. Us, in cold regions where freeze-thaw cycles are common, it is necessary to assess the effects on the strength of sandstone to ensure appropriate integrity and maintenance of engineering projects in such regions [1,2,3,4,5]. In sandstone with initial damage, such as pores and microcracks, the primary effect of freeze-thaw cycles is the generation, propagation, and connection of these existing defects [6,7,8]. It is possible to evaluate these damage mechanisms through triaxial rock tests, mesodamage processes cannot be evaluated adequately. Us, it is necessary to combine macroscopic and mesoscopic methods in order to evaluate sandstone damage mechanics in cold regions It is difficult to observe internal damage in rock materials through traditional means. us, it is necessary to combine macroscopic and mesoscopic methods in order to evaluate sandstone damage mechanics in cold regions
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