Abstract: The freeze-thaw cycle is one of the important environmental factors that accelerate the deterioration of rock material properties,and it is also an important hidden danger that affects the stability and safety of open-pit slope. In order to study the mechanical strength attenuation characteristics and damage effects of fractured mudstone under freeze-thaw cycles,uniaxial compression tests and computed tomography (CT) scanning tests were carried out on mudstone samples after 0,5,10, 20 and 50 freeze-thaw cycles respectively. At the same time,the microscopic damage mechanism of mudstone was studied by scanning electron microscopy. The experimental results show that the uniaxial compressive strength and elastic modulus of mudstone decrease gradually with the increase of the number of freeze-thaw cycles,and the decay rate is most significant at 0~10 freeze-thaw cycles,and then the decay rate gradually slows down. Two-dimensional CT images show that the pore structure of mudstone samples is continuously developed due to freeze-thaw cycles,and the porosity has an exponential and negative linear correlation with cycle times and elastic modulus,respectively. This phenomenon indicates that the accumulation of damage to mudstone mesostructure is significantly correlated with the attenuation degree of macroscopic mechanical properties. Under the action of freeze-thaw cycle,the damage degree of the internal microstructure of fractured mudstone is gradually deepened,and the expansion of cracks and the change of particle contact relationship are the important factors leading to the decline of mudstone strength. The above analysis has a certain reference significance for the design and construction of the open-pit slope in the fractured mudstone distribution area.

Key words: mudstone,freeze-thaw cycle,mesostructure,mechanical properties,mechanism analysis