Study on the Compression Waves Propagating along a Railway Tunnel with Multiple Branch Shafts

초록

In order to reduce the severe pressure transients inside tunnels and improve passenger comfort in high-speed trains, implementation of an array of ventilation branch shafts is suggested. Several studies(1-3) have warranted the implementation of ventilation shafts as there is significant reduction in the steepness of the compression wave which particularly is a desirable effect in tunnel aerodynamics. Furthermore, there is additional usage of the ventilation shafts. These can also be converted into emergency evacuation routes, smoke extraction sites, ventilation, etc., and can be integrated in the tunnel to perform additional tasks. Most importantly, the reduction in the pressure gradient of the compression wave could alleviate the high amplitude micro-pressure waves (MPWs) emitted from the tunnel exit. The first railway tunnel with branch air shafts was installed in Switzerland and has shown to improve passenger comfort by reducing pressure transients inside tunnel2. Later, some already-built tunnels were altered by installing multiple branch shafts along the line(2-4). Branch shafts reduced train-car fatigue that was common in railroad tunnels as the expansion wave reflects back from the far end and propagates towards the entrance. A 2D numerical simulation is carried out here to optimize the shafts by means of studying the characteristics of the compression wave propagating along a tunnel with shafts installed in a continuous array. It is planned to utilize the existing equipment chambers in tunnels as branch shafts during the commissioning phase of three different railway lines, viz. Thaepyong, Shindae and Anbo-II. However, the tunnel's length, the number of branch shafts, the geometry, and the shape of the shafts affect the compression wave characteristics drastically. Nonetheless, the current work uses numerical simulations to evaluate the impact of tunnel length and the number of branch shafts in order to reduce the number of variables. Compression waves at three distinct train speeds―250, 300, and 350 km/hr―are chosen for conducting the 2D numerical simulations.