Micro-pressure wave emissions from German high-speed railway tunnels – an approved method for prediction and acoustic assessment

Abstract

With increasing train speeds, the emission of micro-pressure waves (MPW) from tunnel portals can contribute significantly to the annoyance of residents close to a high-speed railway line. Up to now there are no established assessment guidelines or standards in Europe, with the specific purpose of assessing this effect.In order to develop efficient measures for the reduction of noise emission due to MPW it is necessary to join the planning of a new tunnel at an early stage. This requires reliable prediction methods as well as upper limits for noise levels. As micro-pressure waves are audible as “sonic boom”, the generally used A-weighting is not considered to be a suitable indicator for the evaluation of this effect.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. The main issues were the protection against hearing damage in the close vicinity of the tunnel entrances (e.g. railway workers), the conspicuity in the portal region, the annoyance in residential areas in the surrounding of the railway line as well as micro-pressure effects on the structures of nearby buildings and secondary acoustical effects by structural vibration excitation.As a result of this study, a method for prediction and assessment of MPW-immissions was proposed to the German national railway authority. The final procedure, which has been approved by the German national railway authority (EBA) and the German Federal Environment Agency (UBA), includes following requirements: (I) The C-weighted sound peak level LpC,peak should not exceed 115 dB(C) at a distance of 25 m from the tunnel portal, additionally (II) threshold levels for the C-weighted sound exposure level depending on the utilization of the area should not be exceeded at buildings in the neighborhood of tunnel portals. (III) Above all the A-weighted sound exposure level of MPW in the neighborhood should be evaluated according to the German traffic noise protection directive.The prediction and assessment procedure is adopted into the regulation “Ril 853” of DB Netz AG and came into effect as of Feb, 1st 2013. It is the basis for all current German tunnel projects either in planning or under construction.This paper gives a brief overview of the generation mechanism and the acoustical properties of micro-pressure waves. The prediction method that was developed by DB Systemtechnik will be summarized. It also describes the developed assessment criteria and their justification in regard to the relevant noise legislation. An overview about existing measures for reducing MPW emissions is shown.