Abstract: To explore the macro-mechanical characteristics and damage evolution mechanism of frozen rocks, the CT scanning images of each scanning layer of rock samples are obtained by using CT real-time scanning under uniaxial compression at 20 ℃, ?5 ℃ and ?10 ℃. The grayscale histogram and binary images are generated based on self-programming program in Matlab. The safety, damaging and fracture zones in the scanning layers of the rock sample are defined using the relationship between H value and density. Combined with thermal effect, water softening effect and ice frost heaving pressure on rock sample, the damage evolution law of frozen rock is studied quantitatively. The experimental results show that (1) during the process of temperature drops from 20 ℃ to ?5 ℃ and then to ?10 ℃, the unfrozen water content decreases and the frozen ice content increases. Correspondingly, the rock sample strength increases and the resistance to deformation enhances and the overall stability also enhances. The CT scanning images show that the development of cracks slows down and the rock sample damage gradually weakens; (2) the damage evolution of rocks under uniaxial compression generally experiences different stages including crack initiation, closure, propagation, influx and finally the formation of macroscopic main cracks. Thus the deformation of rock samples increases and damage occurs at different temperatures; (3) due to the end effect, the damage degree of the scanning layers at middle is stronger than that of the end. Besides, the damage formation of the external scanning layers is earlier than that of the internal scanning layers. Damage marginalization occurs and it expands to the inside of rocks.

Key words: frozen rock, CT real-time test, grayscale histogram, binary image, thermal effect, frost heaving pressure, damage evolution