## 3 Results
### Comparison of Results between Model-C and Other Models  
Results from Model-C and other models are compared to determine the influence of initial stress and deformation of slab track caused by frost heave. According to Figure 10, there is also a relatively large difference between the result of Model-C and the other two models. For example, both Model-B and Model-C have taken into account the influence of contact loss area during the calculation; however, the maximum vertical force of Model-C is around 181.74 kN at the time of 0.60 s, which is 30.10% higher than that of Model-B. Moreover, whether the contact loss plays an important role in the difference is debatable. To determine the reason for the difference in wheel-rail force between Model-B and Model-C, the dynamic response of the track structure needed further analysis. When the vehicle passes by the contact loss area, the interlayer gap closes and there is a clapping action between the structural layers. The clapping action between all structures' layers is finally reflected in the interlayers between the foundation plate and subgrade. The contact pressure of the foundation plate-subgrade interlayer is shown in Figure 13. The selected contact layer for comparison is located in the contact loss area (which is described as Position B in Figure 7). It can be seen that the maximum contact pressure of Model-C is not too different from that of Model-B. It is suggested that the contact loss area in Model-C may not be the cause of the increment in the wheel-rail force. Besides this, the time history was very similar in shape and value to that in [24]. Figure 12: Time history of vertical acceleration of the track slab with different models. Figure 13: Time history of interlayer contact pressure with Model-B and Model-C. Figure 13 has demonstrated that the contact loss area is not the cause of the difference between Model-C and Model-B. However, in further analysis, we found that there is also a significant difference in the dynamic displacement of the track slab above the contact loss area in the two models, which may be a key factor to increase the dynamic response of the wheel and rail in Model-C. The time history of vertical displacement with Model-B and Model-C is compared in Figure 14. The selected node for comparison is located above the end of the foundation plate (which is described as Position A in Figure 7). According to Figure 14, the maximum upturned deformation of Model-C is around 4.38 mm, while the result of Model-B is only 2.26 mm. Because the track structure is bent by subgrade, only a small part of the whole foundation plate is supported by the crest of frost heave, and the contact loss area appears in the front and back of the crest, making the slab track more like a lever. When the wheel load compacts the contact loss area in front of the crest, the structure, which is located above the contact loss area in the back of the crest, would appear as an upturned displacement due to the bending stiffness of the track structure. The upturned displacement would be amplified by the bending state of the track slab itself. In the calculation of Model-B, the contact loss area is simply imported, while the track structure is still in normal condition. However, the leverage effect of the slab track is first calculated and the deformation, the stress and the constraint were transferred into the vehicle running analysis in Model-C, which generates a larger upturned displacement of the track structure. In the end, a larger upturned displacement brings larger dynamic irregularity, which leads to a greater vertical wheel-rail force in Model-C. The vertical acceleration of the car body under different cases is shown in Figure 15. Compared with the no frozen case, the vertical acceleration of the car body showed obvious fluctuations after entering the frost heave area. The mode of fluctuation is influenced by the superposition between the dynamic responses of the front and the back bogies, which could also achieve a good agreement with the results in [22; 23; 24].