# Full-Scale Experimental Investigation of the Interaction between Trains and Tunnels
## 1 Introduction  
In the last 40 years, railway transportation has changed considerably mainly thanks to the development of High-Speed (HS) lines and trains. Driven by this trend, interest in aerodynamic effects has grown exponentially, considering that train aerodynamic effects, on first approximation, increase with the square of the train speed. Drag reduction, crosswind effects, head pressure pulses, effect of the slipstream on people at trackside and on platform, pressure transients within tunnels, and the ballast lifting phenomenon [1; 2; 3; 4; 5] are just some of the problems caused by the aerodynamic field surrounding a HS train.  
All the above listed topics have to be considered at the design phase and it is also necessary to take them into account in new standards to ensure run safety. Within joint research projects among several European institutions, significant work has been carried out over the last 20 years to develop both standard procedures and limits gathered in the European standard EN 14067 and in the Technical Specification for Interoperability (TSI) for both rolling stock (RST) and infrastructure (IST) [6; 7; 8; 9; 10; 11; 12]. Nevertheless, at the moment, there are still gaps and open points in standards, and further work needs to be done, considering that in some cases there is not yet a unified standard, and each country is progressing in its own way.  
The present work focuses on the phenomenon of overpressures in tunnel, since it represents one of the most challenging aspects with regards to the train speed increase and the Italian line characteristics. Thanks to the knowledge acquired over more than three years of experimental tests carried out as part of the homologation process of the ETR1000 train (running dynamics, pantograph-catenary interaction, aerodynamics, and infrastructure dynamics were investigated at the same time during an extensive experimental campaign [13; 14; 15; 16; 17]), ad-hoc tests have been designed to study the main aerodynamic issues that are of concern in order to increase the capacity of the Italian HS line and to highlight aspects needing more details in current regulations.  
Despite the fact that phenomenon of overpressures in tunnel is well defined in the European standards, as well as the test procedures required to certify a new train, some aspects need further investigation, as will be shown by experimental data presented in this work. Moreover, probably due to both organizational difficulties and high costs of full-scale tests, there is still a lack in the literature of full-scale data (some examples are reported in [18; 19; 20; 21; 22; 23; 24; 25; 26]) necessary to validate numerical codes that are required in the certification process and are used in train structural dimensioning. In this respect, after investigating the effects of various parameters on the measured pressure, a one-dimensional (1-D) code (TETUN, the 1-D code developed in the AeroTRAIN project to become a European reference) was extensively validated reproducing the numerous available experimental scenarios (single passages of different trains, two train crossing, different tests speed, different tunnel characteristics) and some important results are shown in this work. The research gave the opportunity to compare different physical phenomena producing aerodynamic loads on sealed and unsealed trains, increasing the understanding of the pressure wave generation and transmission.