Optimization of Window Pattern of Tunnel Hood Installed at Long Slab Track Tunnel for Reducing Micro-Pressure Waves

Micro-pressure waves (MPWs) associated with high-speed railways can cause serious environmental problems. The magnitude of the MPWs is proportional to the pressure gradient of the compression wave at the tunnel exit. A compression wave is generated when a train enters a tunnel, and it propagates towards the exit. For a long slab track tunnel, the pressure gradient of the generated compression wave increases during propagation owing to nonlinear effects. The nonlinear effects primarily depend on the pressure gradient of the compression wave at the entrance. Therefore, tunnel hoods are installed in long slab track tunnels in Japan to reduce the pressure gradient. Recently, a rapid numerical method has been developed to calculate the generation and propagation of compression waves based on the nonlinear acoustic theory, which enables optimization of the window pattern of the hoods by considering the propagation of the compression wave for long tunnels. In this study, the window patterns for short and long slab track tunnels were optimized, and the optimum window patterns (OWPs) are shown to be dependent on the tunnel length.