# Full-Scale Experimental Investigation of the Interaction between Trains and Tunnels
## 2 Trackside Tests
### Initial Conditions Influence  
The standard EN 14067-5: 2006 [12] describes how to measure the pressure signature at a fixed location in the tunnel. The indications provided are:  
Figure 3: \(\Delta P_{max}\) measure during the train speed increases as a function of the speed and best fit quadratic line. \"The tunnel should have constant cross section, no airshafts and no residual pressures waves. Ideally there should be no initial air flow in the tunnel. However, if there is, its influence on the measurements should be checked.\"  
If we focus on the second part, it is suggested that a certain dependence on the initial air flow speed is expected, but nothing else is specified: for example, no limit criteria nor data correction procedure are specified. Although the condition of \"no initial air flow in the tunnel\" may be verified during homologation runs, the restrictive request on the flow speed may result in expensive tests, especially if they are performed in a normal day of commercial traffic. Trains crossing a tunnel generate an airflow that remains inside the tunnel also after their passages, adding adverse testing conditions to the ones due to natural ventilation. Therefore, if a dependence on airflow is admitted, an analysis has to be carried out to understand how the initial air flow effects the pressure signature. To underline the differences due to different initial conditions, Figure 4 shows 203 single passages in a 2700 m long tunnel of the same type of HS train in the selected speed range 200-250 km/h, analyzing the initial residual pressures waves and imposing a limit threshold of 20 Pa. In order to highlight the differences due to different initial conditions, in Figure 5, the maximum pressure measured \(\Delta P_{max}\) is reported as a function of the speed. Although the passages have been selected considering the residual pressures waves, the dispersion of the result is quite wide, i.e., it is about 300 Pa and it cannot be explained by the environmental condition. By way of example, in Figure 6, two passages performed at the same speed within only two hours are reported. From the comparison, the differences between the two histories are clearly visible, particularly as regards the \(\Delta P_{N}\) of both the TWS and of the TNS. In the first case, the \(\Delta\)PN is much bigger and the friction region has a larger slope, while, after this first part, the two curves overlap perfectly. In order to better understand the cause, the passages preceding those shown in Figure 6 are also analyzed. The timetable of the four considered passages, together with their direction, is shown in Table 1.  
Figure 4: Superposition of 203 single train passages of the same type of HS train recorded in a 2700 m long tunnel. The differences of the first part of the pressure signature can be explained by the different initial conditions due to previous trains: in the first case, the previous train was run at opposite directions, while in the second one, the train had the same direction as the one analyzed. Unfortunately, in this experimental campaign it was not possible to place an anemometer inside the tunnel and, therefore, it was not possible to directly identify the dependence of the pressure signature on the speed of the flow within the tunnel. On the other hand, the numerical simulations \begin{table}
\begin{tabular}{c c c} \hline
**TIME** & **TRAIN** & **DIRECTION** \\ \hline
15:06:51 & ETR500 & Rm-Fi \\
15:09:58 & Train (a) & Fi-Rm \\
17:32:13 & ETR500 & Fi-Rm \\
17:36:21 & Train (b) & Fi-Rm \\ \hline \end{tabular}
\end{table} 
Table 1: Timetable of the four passages considered in the analysis. Figure 5: Measured \(\Delta P_{max}\) of the 203 single train passages as a function of train speed. Figure 6: Comparison between two time histories of the pressure generated by two trains; same train type, same tunnel, same speeds, same day. also do not account for this effect and, consequently, 1-D codes could underestimate the real values in case of two trains crossing.