## 4 Analysis and Discussion
### Comparative Analysis of Field Measurements and Numerical-Analysis Results
As shown in Figure 18, the result of the Wheel-Rail-interaction-force analysis of the HSR T1 track shows that in the case of the left rail of the HSR T1 track, the maximum dynamic wheel load was approximately 241 kN at a train speed of 120 km/h in the maximum vertical profile section, which corresponds to an increase by \(\sim\)2.01 times compared with the static wheel load. However, at a train speed of 80 km/h, the maximum dynamic wheel load was \(\sim\)151 kN, thus indicating an increase by \(\sim\)88.7% compared with the static wheel load. In addition, the analyses showed that the dynamic wheel load in the left rail was \(\sim\)90 kN larger at the train speed of 120 km/h compared with 80 km/h. In the case of the right rail of the HSR T1 track, the maximum dynamic wheel load was \(\sim\)251 kN when the train speed was 120 km/h in the maximum vertical profile section. This is \(\sim\)2.13 times larger than the static wheel load. However, at a train speed of 80 km/h, the maximum dynamic wheel load was \(\sim\)156 kN, which corresponds to an increase of \(\sim\)95% compared with the static wheel load. In addition, the analyses showed that the dynamic wheel load in the left rail was \(\sim\)95 kN larger at the train speed of 120 km/h than that at 80 km/h. Figure 19 [17] shows the results of the Wheel-Rail-interaction-force analysis of the HSR T2 track. In the case of the left rail of the HSR T2 track, the maximum dynamic wheel load was \(\sim\)230 kN when the train speed was 120 km/h in the maximum vertical profile section, which is \(\sim\)1.88 times larger than the static wheel load. However, at a train speed of 80 km/h, the maximum dynamic wheel load was \(\sim\)146 kN, which corresponds to an increase of \(\sim\)82.5% compared with the static wheel load. In addition, it was analyzed that the dynamic wheel load in the left rail was \(\sim\)84 kN larger at the train speed of 120 km/h compared with 80 km/h. In the case of the right rail of the HSR T2 track, the maximum dynamic wheel load was \(\sim\)477 kN when the train speed was 120 km/h in the maximum vertical profile section. This is \(\sim\)4.96 times larger than the static wheel load. At a train speed of 80 km/h, the maximum dynamic wheel load increased by \(\sim\)2.2 times to \(\sim\)256 kN. In addition, it was analyzed that the dynamic wheel load in the left rail was \(\sim\)221 kN larger at the train speed of 120 km/h than that at 80 km/h. Figure 19: Analysis of Wheel-Rail interaction at different train speeds (HSR T2). (**a**) Left rail; (**b**) Right rail. For general rail surface irregularities, the increase in the dynamic Wheel-Rail interaction is 1.8 times or more depending on the speed, even if it is less than about 1 mm [18]. In this study, the increase is due to the irregularity of the rail surface of 15 mm or more, and because the speed of the train is high. The result of the Wheel-Rail-interaction-force analysis as a function of the track irregularities for each speed range showed that even with the same track irregularities, the level of increase in the dynamic load can yield a considerable difference depending on the train speed. The effect of the train speed was more dominant on the increase of dynamic wheel load compared with the effects of track irregularities. As a result of the correlation analysis between track irregularities and Wheel-Rail interaction force, as shown in Figures 20 and 21, in the section in which track irregularities exceeded the maintenance criteria value, the Wheel-Rail interaction force considerably exceeded the ballasted track representative value and the design load regardless of the train speed [17]. In addition, the Wheel-Rail interaction force exceeded the value of the design load (137.3 kN) by almost two times when the applied track impact factor (V = 120 km/h) was used. In this case, the analysis showed that the Wheel-Rail interaction force was large in the section in which track irregularities did not exceed the maintenance criteria value, but a similar level of vertical profile still occurred.