Measures to counteract micro-pressure waves radiating from tunnel exits of DB's new Nuremberg-Ingolstadt high-speed line

In December 2005, when first test runs were carried out on the new high speed line Nuremberg-Ingolstadt, significant sonic boom incidents occurred at the portals of the 7700 in long Euerwang tunnel and the 7260 in long Irlahull tunnel. Both double-track tunnels with a cross section of 92 m(2) were originally planned to be built with ballasted track. When a change to slab track was decided, no changes in the design of the already built tunnels were introduced. In order to reduce micro-pressure wave emissions and to ensure an in-time start of commercial railway operation, DB decided to take immediate countermeasures by equipping the two tunnels with acoustical track absorbers. These absorbers are designed to counteract railway noise, but also affect via dispersion and friction the pressure wave steepening process. With the installation of these absorbers the wave steepening process was significantly inhibited and, thus, commercial operation could start successfully in May 2006 without operational restrictions. A simplified formula based on the solution for the vibrating piston which was developed at RTRI appears to be well suited for the prediction of the amplitude and frequency content of the emitted micro-pressure wave in the vicinity of the tunnel portal.