The pressure changes associated to these waves can have an effect on the passengers if the trains are not suitably sealed or pressurized. The intensity of the waves depends mainly on the train speed, and on the blockage ratio (train-section-to-tunnel-section area ratio). As the intensity of the waves is limited by regulations, and also by the effects on passengers and infrastructures, the sizing of the tunnel section area is largely influenced by the maximum train speed allowed in the tunnel.

The aim of the study presented in this paper is to analyze the increase in cost of a tunnel due to the existence of this difference in ground level, and evaluate the increase of construction costs that this elevation might involve. The analysis of the tunnel construction cost is performed based on the results from Peláez and Montenegro [1].

A preliminary analysis of the tunnel cost is realized taken into account the pressure jump at the nose of the train at the tunnel entrance and the hydrostatic pressure. To evaluate the pressure jump an analysis of the formulae proposed in the references contained in the paper's bibliography has been carried out.

The train wave signature (TWS) method detailed by William-Louise and Tournier [2] is used to obtain the initial conditions to run the program Thermotun. The shape of the train-tunnel-pressure signature used in this method is detailed in CEN EN 14067-5 [3].

The critical cross-sectional area of the tunnel for a train entering at 300 km/h in a tunnel with an ascendant slope of 25/1000 and length over 20 km is determined by the health criterion which implies that the maximum pressure variation along the train shall not exceed 10 kPa during the time taken for a train to pass through the tunnel.

It is demonstrated that the tunnel cost increases exponentially with the hydrostatic pressure and has an asymptote when the change in altitude reaches 10 kPa.

1

M. Peláez, N. Montenegro, "Pressure wave measurements inside tunnel of the spanish railway network and inside a high velocity streamlined test train", ITA-AITES World Tunnel Congress, Budapest, 2009.

2

M. William-Louis, C. Tournier, "A wave signature based method for the prediction of pressure transients in railway tunnels", J. Wind Eng. and Ind. Aerod., 93, 521-531, 2005. doi:10.1016/j.jweia.2005.05.007

3

CEN, EN 14067-5, "Railway applications - Aerodynamics - Part 5: Requirements and test procedures for aerodynamics in tunnels", 2006.

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