Page 347 - 360.revista de Alta Velocidad - Nº 5

Influence of Aerodynamics in Tunnels Design

This limitation of C - weighted "noise" production is based on the fact that most of the energy
produced by micro - pressure waves is at low frequencies (<100Hz) and even in the infrasound
region (<20Hz). As it will be seen later, the frequency weights "clean" the sound pressure level
(SPL), let us call it "raw noise", leaving only the noise produced in the desired frequency ranges
so that it can be analyzed better. This cleaning is done by subtracting from the SPL noise a value
(WC) of "decibels" for each frequency. This Wc value is determined by a formula that depends
on the frequency at which it is found (f).
Therefore, using the "noise" produced in C-weighting allows the clear analysis of noise produced
only by micro-pressure waves.

6.3 Innovative project

In INECO, a tool called PROTAV has been developed, through the Innovation Directorate and
thanks to the collaboration of the Ignacio Da Riba Institute of the UPM (Polytechnic University
of Madrid) in Madrid, able to predict and attenuate the effect of the sonic boom.

To carry out this project the following steps were developed:
• Instrumentation of a tunnel in which sonic boom was produced
• Modelling of this tunnel and checking in the tool.

• Check using the tool if this effect occurred in tunnels in which the effect of micropressures
does not occur.

The following parameters were measured:

• Distribution of pressure and air velocities in the tunnel.
• Static sound produced by the impact of the shock wave generated at the tunnel entrance
when Mach 1 speed is reached.

The main objective of these measurements has been the evaluation of the Sonic Boom that
produces the pressure wave generated by the trains at their entrance to the tunnel when it
reaches the exit portal.

6.4 Cabrera tunnel features

The La Cabrera tunnel belongs to the LAV Madrid - Valencia / Albacete. It is a single-track
twintunnel. Its most important characteristics are the following:

• Length: 7229m

• Cross-Section Type: Circular - Bitube of 53m2

• Input Line ch: 351 + 277 at 624m height

• Output Line ch: 358 + 506 at the 461m height

• As for the longitudinal profile according to increasing chainage is characterized by a
slope of -30 ‰ during the initial 2.3km, then changes its slope to -8 ‰ for 1.1km, to finish
with a slope of -25 ‰ rest of the tunnel.

International Congress on High-speed Rail: Technologies and Long Term Impacts - Ciudad Real (Spain) - 25th anniversary Madrid-Sevilla corridor 345