Experimental study on the effect of heat release rate and aspect ratio of tunnel on the plug-holing phenomena in shallow underground tunnels

In this study, we experimentally investigated the effect of heat release rate and aspect ratio of tunnel on the plug-holing phenomena in a reduced-scale model tunnel. In the view of physics, plug-holing phenomena was analyzed to develop the new modified Froude number considering the tunnel and shaft geometrics and the heat release rate of fire for natural ventilation system. As the results, plug-holing occurred when the new modified Froude number is below 2.75. Also, when the heat release rate increased or the aspect ratio decreased, the modified Froude number decreased. The new modified Froude number might have greater flexibility and be more accurate for various tunnel fire situations compared with the existing criteria to judge the occurrence of plug-holing.