Understanding the mechanical properties and multiscale failure mechanism of frozen soft rock is an important prerequisite for the construction safety of tunnels, artificially frozen ground and other infrastructure in cold regions. In this study, the triaxial compression test are performed on mudstone in the weakly cemented soft rock strata in the mining area of western China, and the mechanical characteristics and failure mechanism of weakly cemented mudstone are systematically investigated under the combined action of freezing and loading. Furthermore, the quantitative relationship between the microstructural parameters and the macroscopic strength and deformation parameters is established based on fractal theory. Thus, the failure mechanism of frozen weakly cemented mudstone is revealed on both micro- and macro-scales. The results show that temperature and confining pressure significantly affects the elastic modulus and peak strength of weakly cemented mudstone. With decreasing temperature, the compressive strength increases, while the corresponding peak strain decreases gradually. On the deformation curve, the plastic deformation stage is shortened, and the brittle fracture feature at the post-peak stage is more prominent, and the elastic modulus correspondingly increases with decreasing temperature. Under low-temperature conditions, most of the weakly cemented mudstone undergoes microscopic shear failure along the main fracture surface. The micro-fracture morphology characteristics of weakly cemented mudstone under different temperatures are quantified via the fractal dimension, and an approximately exponential relationship can be obtained among the fractal dimension and the temperature, compressive strength and elastic modulus.

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Keywords: Weakly cemented mudstone, Artificial freezing, Mechanical properties, Linkage destruction mechanism, Fractal dimension