HS2’s breakthrough tunnel design (RailEngineer)

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Take a look at the latest images of the trains proposed for HS2. They too have to travel very fast – just as fast as, if not faster than, their Japanese counterparts. The HS2 trains also have panache, but their noses are far more ‘Audrey Hepburn’ in comparison. So, what is going on? Why have the very savvy Japanese embarked on such prominent nose jobs whilst the Brits are so nasally understated?

The basic reason is because HS2 will be tailoring new rolling stock to suit its new infrastructure, while the Japanese have had to tailor new rolling stock to suit existing infrastructure.

A bit of background

When the Shinkansen railway was extended in the 1970s, those living near the portals of one of the new tunnels were disturbed by loud bangs that occurred a short while before a train emerged. Technically, these are known as micro-pressure waves. To the press, they quickly became known as ‘sonic booms’. Something had to be done.

The German solution. West portal of the Finne tunnel, designed for 300km/h, built 2011 and opened for service 2015.

Tunnel hoods

The engineers quickly analysed the problem and realised that they had to slow down the build-up of pressure in front of the train before it entered the tunnel mouth. To do so, they designed and retro-fitted hoods for the tunnel portals that would guide the air as the train entered. Without these measures, the pressure wave would build up too quickly and, after travelling down the tunnel bore at the speed of sound, would emerge at the other end.

The world learnt from the Japanese experience and just about all of the long tunnels on subsequent lines have been fitted with hoods of one pattern or another.

As a result of this experience, sonic booms are something that designers of all high-speed lines are mandated to avoid. This, of course, includes HS2.

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Written by Long Branch Mike