## 1 Introduction  
In recent years, with the steady progress of China's 'western development' strategy, a large number of water conservancy and hydropower projects, railways, highways, oil pipelines, and other engineering projects have been built in the western high-cold mountains. The frost damage to high and steep slopes, subgrades, tunnels, and building foundations poses a great challenge to the engineering construction and maintenance. The field of frozen soil mechanics has been studied for almost 70 years [1, 2, 3, 4, 5, 6]. According to previous engineering experience, the formation of frozen soil is frequently accompanied by frozen rock issues, while the study of frozen rock is relatively new. Under the influence of periodic temperature changes for many years, the pore water in the rock mass has experienced repeated frost-heave and thaw-shrinkage processes. This also causes the original fractures inside the rock mass to continuously expand to a certain depth. Rock mass will be destroyed and degraded under varying temperatures and water content, resulting in geological disasters such as landslides [7, 8, 9, 10, 11, 12]. According to the specific characteristics of rock slope engineering, it is necessary to carry out corresponding research on frozen rock mechanics. Here, the research status of freeze-thaw problems will be briefly introduced and analyzed. (1) In the investigation of the physical and mechanical properties of rock during the freeze-thaw cycle, [PERSON] et al. first pointed out that human research on frozen rocks began with the recognition of the frost heaving and thawing of ice in the 19 th century. Frost heave, capillary water movement, and lithological variations are the main causes of freeze-thaw damage to rock masses [13]. [PERSON] et al. analyzed the evolution law of the uniaxial compressive strength of rocks in different freeze-thaw temperature ranges [14]. [PERSON] et al. conducted uniaxial and triaxial compression tests on sandstone under single freeze-thaw conditions at various temperatures, observing that frost-heave deformation in dry samples is elastic, whereas it is the opposite in saturated samples. Furthermore, freeze-thaw samples have a higher elastic modulus and higher compressive strength than unfrozen ones [15]. [PERSON] et al. pointed out that the variation law of rock parameters after a freeze-thaw cycle is determined by the initial state and porosity of the rock [16]. [PERSON] et al. assessed the long-term durability of Iranian red sandstone after 30 freeze-thaw cycles and proposed that the distribution law of pores plays a significant role in the degree of freeze-thaw damage in red sandstone [17]. [PERSON] et al. considered Brazilian tensile strength to be a critical criterion for determining the durability of freeze-thaw rocks [18]. [PERSON] et al. carried out 300 freeze-thaw cycles on granites from three different origins, compared and analyzed the evolution laws of various physical and mechanical parameters, and concluded that the longitudinal wave velocity is the best index for evaluating the physical and mechanical properties of freeze-thaw granite [19]. The impacts of freeze-thaw cycles on the physical and mechanical properties of some sedimentary rocks in Turkey were investigated by [PERSON] et al. The freeze-thaw cycle causes sample porosity to rise while decreasing point load strength, Schmidt hardness, and weight. The point load strength loss and the Schmidt hardness loss have a strong relationship after 20 cycles, which is highly useful for estimating the point load strength following freeze-thaw cycles [20]. In brief, the main trends in the research on the physical and mechanical properties of rock freeze-thaw are as follows: The freeze-thaw cycle treatment methods change from a single freeze-thaw cycle and a single temperature gradient to different cycles and different temperature gradients. The test method has progressed from the uniaxial compression test to the conventional triaxial compression test and then to the triaxial compression unloading and creep tests.