Analysis of water and ice content during rock freezing based on the three-valued segmentation of frozen rock CT images

摘要

The proportion relation of unfrozen water and ice content dominates thermal and mechanical properties of frozen rock.Any change of unfrozen water and ice content will affect mechanical properties of frozen rock significantly even violently.Existence of ice causes that physical and mechanical properties of frozen rock strongly dependent on temperature, moreover, result in complex macroscopic mechanical response.Therefore, studying water and ice content of rock during freezing has a significant effect on the security and stability of the rock engineering in cold region.CT scanning images of sandstones at different low temperature are obtained by carrying out the CT scanning experiment at 20℃, 0℃,-5℃,-10℃,-20℃ and-30℃.The double thresholds segmentation that based on genetic algorithm is realized and the three-valued segmentation of frozen rock CT images is completed.The three-valued segmentation of frozen rock CT images is employed to distinguish water and ice from rock in the internal of frozen rock.Digital expression of spatial location and the content of water, ice and rock are given definitely by the three-valued segmentation.Three-valued segmentation of frozen rock CT images are statistically analyzed.In frozen rock, the unfrozen water content is considered as an internal variable and the work conjugated with the internal variable is the latent heat of phase change of unfrozen rock.The continuum thermodynamic theory is employed to deduce the formula of the relationship between the unfrozen water and ice content depends on temperature.The proposed formulas are verified according to the Computed Tomography (CT) scanning experiment of frozen rock at different minus temperature.The results shows that: (1) The experimental results of CT scanning agree well with the result predicted by deduced formula.The change of unfrozen water and ice content in the process of freezing can be described by deduced formula, and the pure frozen point of frozen rock can be predicted.(2) The content of water occurrence freezing depends on temperature, also concerned with other factors, such as specific surface area and pressure.(3) Unfrozen water and ice content in rock interior varied with the changes of temperature, and both are in a state of dynamic balance.