# Dynamic Characteristics of Sandstone under Coupled Static-Dynamic Loads after Freeze-Thaw Cycles
## 1 Introduction  
When rocks are subjected to freeze-thaw weather, in the freezing process, the water undergoes an ice phase volume expansion which produces a freezing force acting on the rock matrix [1]. The freezing force has an important impact on the stability of rock deformation engineering, and because of the influence of the freezing force, crack development results in internal rock damage. In the absence of an engineering disturbance, the rock mass is in an equilibrium state. When human engineering activities are carried out, such as excavation blasting, disturbing the balance, rock deformation movement results in small-scale cracks that propagate through each other causing macro-scale cracks and failure. In 2013, the China Tibet Jiama mine slope landslide was caused by the collapse of more than 2 million cubes due to freeze-thaw and dynamic loading, resulting in serious casualties and property losses [2]. In addition, Chinese western development, infrastructure construction, and cold geotechnical engineering will encounter an increasing number of problems. Therefore, it is very important to study the dynamic characteristics of rock masses under the action of the freeze-thaw cycle, which is significant in the study of rock mechanics theory and practical application of rock mass engineering. With the accelerated development of the economy, construction has rocketted in high altitude and cold regions. In this area, rock behavior under freeze-thaw cycles is a puzzling problem for engineers in many fields, such as road, railroad, open pit, and civil engineering [3,4]. Current studies show that the mechanical properties of rock are severely affected by freeze-thaw cycles, unlike conventional rock [5,6]. Therefore, scholars have conducted many studies on the mechanical properties of rock after multiple freeze-thaw cycles. For example, through contrast tests on dry and saturated granite and anddesite after freeze-thaw cycles (\(-\)16 to +20 \({}^{\circ}\)C), [PERSON] and [PERSON] studied the relationship between the elastic modulus and temperature [7]. [PERSON] designed experiments in which the rock samples were partially immersed in water, and found that the internal microstructure of frost action is the decisive factor causing damage after freeze-thaw cycles for a variety of rocks (including igneous, sedimentary, and metamorphic rocks) [8]. In order to observe the damage in the microstructure of the rock, some advanced technology techniques such as X-ray computed tomography (X-ray CT), scanning electron microscope (SEM), nuclear magnetic resonance (NMR) are commonly used to analyze the evolution of the microstructure under freeze-thaw cycles [9, 10, 11, 12, 13, 14, 15, 16, 17]. [PERSON] and [PERSON] determined the relationship between pre-existing rock flaws and freeze-thaw destruction in different types of sedimentary rock after freeze-thaw cycles and identified four types of freeze-thaw damage [18]. [PERSON] et al. found that when the degree of saturation exceeded 70%, the rock was damaged significantly, and failure can start at the area with a higher degree of saturation through welded tuff with a degree of saturation from 0% to 95% [1]. [PERSON] et al. conducted an experiment studying the static mechanical properties of degradation of granite under freeze-thaw cycles [19]. However, rock mechanics engineering has to account for not only complex and freeze-thaw cycling environments but also for various types of static load and dynamic disturbances in cold areas, such as in situ stress, blasting in the rock mass of the slope, and earthquakes. Therefore, studying the dynamic mechanical properties of the rock under the dual effects of freeze-thaw cycles and static load has important theoretical and practical value for guiding construction in cold regions and preventing freeze-thaw disasters.