Abstract
When a train enters a tunnel, a pressure wave is generated and it travels between both portals of the tunnel. The pressure change in a tunnel is closely related to the problems of aural discomfort to passengers, the strength of car body structure, and so on. When the pressure wave travelling in a tunnel arrives at the tunnel exit, a pressure pulse we name “micro-pressure wave” is radiated from the tunnel exit, raising a new environmental problem. The micro-pressure wave depends on the shape of the pressure wave arriving at the tunnel exit; it is nearly proportional to the pressure gradient of its wave-front. This article deals first with an analysis of the pressure change in a tunnel, next with the radiation of the micro-pressure wave and an analysis of the distortion of the wave-front of the pressure wave as it travels in a tunnel.
