Influence of the shape and size of cavities on pressure waves inside high-speed railway tunnels

For safety reasons, most newly built tunnels are designed as twin-tube tunnels with interconnecting tubes, so that it is possible to rescue passengers inside of one tunnel tube through the other tube in case of an emergency. The interconnections are closed towards the tunnel with safety doors. These doors have to withstand high pressure loads caused by passing pressure waves and can even be damaged because of the waves. The doors are installed in niches which are embedded in the tunnel walls. The influence of the geometry and size of these cavities on the pressure waves and consequently the loads on the doors was studied by means of moving-model rig experiments at the Tunnel Simulation Facility Gottingen. Different cavity configurations and train velocities were examined regarding the loads on a generic door. Furthermore, numerical simulations were performed in order to extend the parameter range, e.g. the tunnel length, and to compare with the experimental results. Although the niches were assumed to reduce the pressure loads on the door, it was found that the pressure at the doors and therefore the loads were increased. The reason for this increase were pressure waves generated due to reflections at both ends of the cavity and the tunnel entry. The waves superpose with the initial wave leading to high pressure amplitudes.