## 5 Conclusions  
Model testing of the failure of steep fractured rock mass under freeze-thaw conditions is carried out using the left abutment slope of a hydropower station as the prototype. Under the freeze-thaw cycle, the evolution rules of the temperature field, slope deformation, frost-heave force, and macroscopic deformation features of the slope are investigated. Numerical simulations are used to investigate the rules of fracture propagation and the effects of freezing rates on slope deterioration. The following are the main conclusions.  
The heat is transmitted from the outside to the inside of the slope. The rate of temperature change varies depending on depth; the closer to the surface, the faster the rate of change, and the shape of the temperature curve is closest to the air temperature. The temperature change rate is slower and the temperature curve is smoother farther away from the slope surface.  
Within the cold storage unit's temperature range, it is evident that unfrozen water is always present at the bottom of the crack during the cooling process; thus, a strategy for inserting an osmometer in the unfrozen water to measure the frost-heave force is designed. During the cooling process, the osmometer's reading rises in a fluctuating manner. The water-ice phase change produces a small amount of frost-heave power. The osmometer's maximum reading is 19.3 kPa, which is equal to 3.17 MPa for the prototype slope frost-heave force. This test also presents a new way to measure frost-heave force.  
The steep fracture opens to the free side during the cooling process due to the frost-heave force induced by water-ice phase change. During the heating process, the cracks are subjected to shrinkage deformation due to solid ice melting. The crack tip expands when the frost-heave force reaches a certain value, and the crack propagation shape is mainly a circular arc. When the intact rock mass's strength is insufficient to withstand the  
Figure 13: The evolution of the minimum principal stress of typical elements under different ice contents.  
sliding force, the rock mass continues to expand along the potential sliding direction until an independent sliding body is formed.  
The numerical simulation results reveal that under the action of frost-heave force, the tensile stress at the crack tip is concentrated, and crack initiation occurs when the tensile stress reaches the tensile strength of the rock mass. The crack grows further into the rock mass as the temperature drops, resulting in a connection between the original crack and the weak interlayer, forming a large sliding plane and eventually causing a landslide disaster.  
Conceptualization, J.Z. and D.X.; methodology, J.Z.; software, B.W.; validation, J.Z., D.X. and B.W.; formal analysis, J.Z.; investigation, C.L.; resources, J.Z.; data curation, C.L.; writing--original draft preparation, J.Z.; writing--review and editing, D.X.; visualization, B.W.; supervision, B.W.; project administration, B.W.; funding acquisition, J.Z. All authors have read and agreed to the published version of the manuscript.  
This study was supported by the National Natural Science Foundation of China (Nos. 41877280, 12072047) and the National Key R&D Program of China (No. 2018 YFC0407002).  
Not applicable.  
The authors declare no conflict of interest.