Acoustic Assessment of Micro-pressure Wave Emissions from High-Speed Railway Tunnels
With increasing train speeds, the emission of micro-pressure waves from tunnel portals, when high-speed trains enter the tunnel at the opposite side, can contribute significantly to the annoyance of residences near a high-speed railway line. In Europe at present no established assessment guidelines or standards exist explicitly devoted to this effect. Counter-measures can be applied to the tunnel portals or to the tunnel interior.
Appropriate consideration of measures to reduce the emission of micro-pressure waves at a very early stage of the planning process requires a prediction method and upper limits for noise levels. As micro-pressure waves are audible as “sonic boom”, the generally used A-weighting leads to inappropriate results.
During the years 2007 to 2009 Deutsche Bahn performed a study how to predict the micro-pressure effects for new tunnel constructions as well as how to assess and to limit the micro-pressure effects. Main issues were the physical condition of humans in the close vicinity of the tunnel entrances (e.g. railway workers), the conspicuity in the portal region, the annoyance at residential areas in the vicinity of the railway line as well as micro-pressure effects on the structures of neighboring buildings and secondary acoustical effects by structural vibration excitation.
As a result, a set of two quantities and guidance levels were suggested. The following levels should not be exceeded: (I) At a distance of 25 m from the tunnel portal the C-weighted sound peak level L pC,peak of 115 dB(C) and (II) in dwellings in the neighborhood of tunnel portals the C-weighted sound exposure level L CE of 75 dB(C). The method is currently applied for all tunnels on high-speed lines, which are currently in the planning phase in Germany.
KeywordsSound Pressure Level Tunnel Entrance Tunnel Exit Slab Track Sonic Boom
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