RTR 4/2010 29 The Leipzig City Tunnel train are transmitted via the track, causing resonance in the tunnel side wall, 2. Transmission: the vibration of the tunnel side wall is transmitted to the foundations of buildings, and 3. Immision: transmission through the building, resulting in the vibration of ceilings and causing secondary airborne noise in rooms. Vibration-generating machines were placed in the tunnel tubes and used to simulate the excitations caused by railway operations, namely for different mass-spring systems, and the way these vibrations were transmitted through the ground to the adjacent buildings was measured. This made it possible to produce forecasts of the effects of vibrations. It was not only the vibrations caused by the railway operation that were recorded but also those due to road traffic (including those caused by trams), and suitable mass-spring systems were deduced from this. A light mass-spring system was selected for the section between the stations of Bayerischer Bahnhof and Wilhelm-Leuschner-Platz and also under the shopping centre at LeipzigHauptbahnhof, while a heavy mass-spring system was selected for the sections between them. The systems used are shown in Fig. 5. The light mass-spring system (floating slabs) is suspended over the whole of its area and has a natural frequency of 15–25 Hz. It thus manages to deaden its own structureborne noise within the uncritical frequency band of up to 30 dB. It is characterised by a simple, fast and favourably-priced construction method and offers advantages in the damping of structure-borne noise in the track-support structure, and the entire system has a high horizontal stability. It is possible for a load to be transferred to the subsoil over a large area. The track support slabs of the heavy massspring-system (natural frequencies 6-8 Hz) are produced with in-situ-cast concrete and are raised after hardening. The punctiform bearings are inserted through openings in the slab. In dimensioning the relatively small load-bearing area, it is important to pay attention to the transmission of the high horizontal forces caused by the operation of trains. This mass-spring system satisfies the most severe demands as regards protection against noise and vibrations with a 20-dB damping of structure-borne noise. Fig. 4: Western tunnel tube Fig. 5: Types of track used Leipzig City Tunnel Southern ramp Western bore Eastern bore Ballasted track Light mass-spring system (15 Hz) Heavy mass-spring system (6 Hz) Slab track Light mass-spring system (25 Hz) Heavy mass-spring system (8 Hz) L E G E N D Tunnel mouth Western ramp Northern ramp Shield tunnelling Ramps – cut-and-cover Station – cut-and-cover Platform Road Tunnel driven under building
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