###### Abstract  
In high-elevation mining areas, the roadbeds of certain surface ore haul roads are predominantly composed of sandstone. These sandstones are exposed to cold climatic conditions for long periods and are highly susceptible to erosion by the effects of freeze-thaw, which can degrade their support properties. This paper investigates the mechanism of strength deterioration of sandstone containing prefabricated cracks under cyclic loading and unloading after experiencing freeze-thaw. Sandstone specimens containing prefabricated cracks were prepared and subjected to 0, 20, 40, 60, and 80 freeze-thaw cycle tests. The strength changes were tested, and the crack extension process was analyzed using numerical simulation techniques. The study results show the following: 1. The wave propagation speed within the sandstone is more sensitive to changes in the number of freeze-thaw cycles. In contrast, mass damage shows significant changes only when more freeze-thaw cycles are experienced. 2. As the number of freeze-thaw cycles increases, the frequency of energy release from the numerical model accelerates. 3. The trend of the Cumulative Strain Difference (\(\varepsilon_{c}\)) reflects that the plastic strain difference between numerical simulation and actual measurement gradually decreases with increasing stress cycle level. 4. With the increase in freeze-thaw cycles, the damage morphology of the specimen undergoes a noticeable change, which is gradually transformed from monoclinic shear damage to X-shaped conjugate surface shear damage. 5. The number of tensile cracks dominated throughout the cyclic loading and unloading process, but with the increase in freeze-thaw cycles, the percentage of shear cracks increased. As the freeze-thaw cycles increase, sandstones are more inclined to undergo shear damage. These findings are important guidelines for road design and maintenance in alpine mining areas. freeze-thaw; PFC; cyclic loading and unloading; damage evolution; crack extension 2025157  
of the rocks after freeze-thaw with the help of the scanning electron microscope (SEM) technique. [PERSON] et al. [4] carried out freeze-thaw tests on cracked sandstones in two ways, namely, water-saturated and ice-saturated, and analyzed the crack extensions under the action of freeze-thaw by applying the CT scanning method. [PERSON] et al. [5] investigated the damage during freeze-thaw of sandstone under different hydration environments with the help of nuclear magnetic resonance and acoustic emission techniques. [PERSON] et al. [6] analyzed the generation of freeze-thaw rock cracks using the laser scanning microscope and digital image correlation (DIC) analysis techniques. They found that the cracks' depth, width, and surface area were positively correlated with the number of freeze-thaw cycles. The above studies have achieved excellent results. However, these methods have limitations in observing the spatial location and sequence of crack generation, which can be effectively solved using particle flow numerical simulation software [7]. Particle flow numerical simulation software is based on the discrete element method, which can observe the occurrence and evolution of cracks from a microscopic point of view and has certain advantages in studying crack extension. Using particle flow software to simulate rock freeze-thaw, researchers can visualize and analyze the types of cracks, crack extension paths, and energy conversion mechanisms generated during this process. Therefore, many scholars have carried out research in this area. Some scholars [8] innovatively adopted the Particle Expansion Model (PEM) to simulate the freeze-thaw effect inside the rock due to the change of freezing and swelling force and achieved remarkable results. Meanwhile, some scholars have simulated the freeze-thaw cycle of rocks using the built-in thermal calculation module of PFC6.0 software.