## 2 Physical Model Testing of Freeze-Thaw Damage and the Deterioration Mechanism of Slope Rock Mass
### Determining Similar Materials  
Because the weak interlayer is located in class III rock mass, determining the physical and mechanical properties of this rock mass will be crucial to the development of this physical model. The parameters of the class III rock mass are comprehensively determined according to the in situ field testing and the field rock mass quality classification carried out for the above-mentioned project.  
In order to make the parameters of similar materials meet the similarity theory and reproduce the freeze-thaw failure process indoors, gypsum and water are selected as raw materials to simulate the rock mass. According to the above quasi rock mass physical and  
Figure 1: Geological map of the left bank slope.  
Figure 2: Physical model diagram (cm). II: Class II rock mass. III: class III rock mass. IV: class IV rock mass.  
mechanical parameters, after many tests, the mixture ratio of model material is determined as gypsum:water = 1:0.7. Table 1 provides the main physical and mechanical parameters of model materials corresponding to this mixture ratio. Since the class II rock mass is mostly distributed below the fault and is less affected by the freeze-thaw cycle, the mixture ratio of class II rock mass model material is set as 1:0.6. As the texture of class IV rock mass is relatively loose, some stacked gypsum precast blocks with a mixture ratio of 1:0.6 are selected to represent it. The size of the precast block is 240 mm long, 115 mm wide, and 53 mm high. The material of the weak interlayer f2 is simulated by the high molecular water-absorbing resin, its cohesion is c = 1 kPa, and its internal friction angle is \(\varphi\) = 13\({}^{\circ}\). The weak interlayer f3 is a prefabricated crack with a width of 1 cm, and the crack surface is pasted with polyethylene film for waterproofing. During the test, water is filled into the weak interlayer to simulate the water-ice phase change process when the water content is high.  
To verify whether the physical and mechanical properties of the model materials meet the basic requirements of similar materials, the following similarity constant relationship is established in combination with similarity theory:  
\[\left\{\begin{array}{l}C_{\sigma}=C_{\gamma}C_{L}\\ C_{t}=C_{f}=C_{\mu}=1\\ C_{\sigma}=C_{E}=C_{c}=C_{R_{c}}\end{array}\right. \tag{1}\]  
where \(C_{\sigma}\) is the stress similarity constant; \(C_{\gamma}\) is the unit weight similarity constant; \(C_{L}\) is the geometric similarity constant; \(C_{\epsilon}\) is the strain similarity constant; \(C_{f}\) is the similarity constant of the internal friction angle; \(C_{\mu}\) is the Poisson's ratio similarity constant; \(C_{E}\) is the deformation modulus similarity constant; \(C_{c}\) is the cohesion similarity constant; and \(C_{Rc}\) is the compressive strength similarity constant.  
Table 2 shows the actual and theoretical similarity constants. The physical and mechanical properties of the model material basically meet the similarity constant relationship, and the small deviation in the similarity relationship does not affect the qualitative analysis of the test results. The material can be used to simulate the prototype slope to preliminarily explore its freeze-thaw failure law.