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Appendix ANNEX B MAXIMUM PRESSURE VARIATIONS IN TUNNELS

United Kingdom

Original text. Later amendments are not shown.

A significant number of tunnels (both twin and single track) exist on the certain stretches of the high-speed network that can be passed through at maximum line speed.

When a train enters a tunnel, pressure waves are created in the tunnel that rebound from the tunnel ends. For health reasons, the effects of pressure waves experienced by passengers and train staff shall be limited.

The extent of the phenomenon depends on a number of parameters, of which the following are specific to the rolling stock:

  • the ratio between the train and tunnel cross-sections,

  • the shape of the nose of the train,

  • the coefficient of friction between the train and the air flow in the tunnel,

  • the length of the trainset,

  • the shape of the train end.

The aerodynamic characteristics of a trainset vis-à-vis the generation of pressure waves in a tunnel can be created from the pressure variation in the tunnel at the time of the train's total entry into the tunnel.

The train can be defined by an envelope curve signature unique to that provided by the three pressure variations P0, P1 and P2. An example of these values can be found on the curve below.

Pressure variation at a point within the tunnel.

Envelope curve unique to the trainset.

Take these values at 250 km/h

  • ΔP0 < or = 1 800 Pa,

  • ΔP1 < or = 3 200 Pa,

  • ΔP1 - 0,8ΔP0 < or = ΔP2.

These values are given by a blocking ratio between the train and tunnel cross-sections of 0,18.