Study on the Compression Waves Propagating in Real High-speed Railway Tunnels with Multiple Branch Shafts

초록

It has frequently been suggested to employ multiple ventilation branch shafts in railway tunnels to reduce pressure transients and enhance passenger comfort in high-speed trains. Furthermore, pressure relief branch shafts can be combined with additional functions such as emergency exit paths, smoke extraction points, ventilation, etc. Alongside these advantages, potential drawbacks that come with the installation of branch shafts include noise emissions. Nonetheless, the first of its kind railway tunnel with branch air shafts that proved to improve passenger comfort opened in Switzerland, running between Mattstetten and Rothrist. Later, many existing tunnels were modified to employ branch shafts along the line. Branch shafts not only improved passenger comfort but also reduced train-car fatigue that frequented in railway tunnels longer than 30 kilometres. Compression waves propagating along railway tunnels undergo viscous dissipation due to wall skin friction. On the contrary, in very long tunnels, compression waves nonlinearly steepen to emit from the tunnel exit as high amplitude micropressure waves (MPWs). Studies on array of air chambers embedded on tunnel tracks have proven to be beneficial in reducing the pressure gradient of the compression wave and thereby alleviate undesirable MPW emissions. Thus, computational study is undertaken here to understand the characteristics of the compression waves propagating in a railway tunnel with embedded multiple branch shafts. The branch shafts otherwise proposed to be used as equipment chambers in tunnels are considered here for the current study. In the commissioning phase of railway tunnels in South Korea, it is projected to use the existing equipment chambers as branch shafts for reducing the pressure gradient of the compression wave. However, the characteristics of the compression wave are dependant on the length of the tunnel, number of branch shafts and the geometry and shape of the shafts. To restrict the number of variables, the current study assesses the effect of tunnel length and number of branch shafts using numerical simulations. 2D numerical simulations are conducted and compression waves for three different train speeds are selected, viz. 250, 300 and 350 km/hr.