Macro and micro damage characteristics of Red-bed sandstone in Urumqi under freeze-thaw cycles.

Investigating the macro and micro structural damage characteristics of red-bed sandstone under freeze-thaw cycles is crucial for guiding construction in seasonal frozen soil regions. This paper analyzes the macro and micro damage characteristics of red bed sandstone in Urumqi area under the action of freeze-thaw cycle through micro-test and uniaxial compression test.The results show that with an increase in freeze-thaw cycles, the porosity and permeability of red-bed sandstone (RBS) samples gradually increase and eventually stabilize.The phase composition of red-bed sandstone samples can be divided into two categories: rock skeleton and cement. When the number of freeze-thaw cycles is 3 ~ 5 times and 20 ~ 25 times, the rock skeleton material is the main loss material. At this stage, due to the large damage of the rock skeleton, the deterioration of mechanical properties is obvious.According to the downward trend, it can be divided into three stages. When the number of freeze-thaw cycles is 0 ~ 5 times and 20 ~ 25 times, it is the severe failure stage. When the number of freeze-thaw cycles is 5 ~ 20 times, it is the slow failure stage.As the number of freeze-thaw cycles increases, the maximum value of the fractal dimension of the middle section of the sample gradually increases, and as the number of freeze-thaw cycles increases, the fractal dimension of the middle section of the sample changes from uneven to uniform.The research results are of great significance to guide the construction of seasonal frozen soil area.