Numerical simulation study on shaft plug-holing height during natural smoke evacuation in deep buried tunnels

Abstract

In this paper, we investigate the plug-holing phenomenon under the influence of natural smoke venting in deeply buried tunnel shafts using a fire dynamics simulator based on a large eddy simulation model. Additionally, we discuss the effects of heat release rate and shaft height. The results indicate that the temperature distribution of the smoke upstream of the fire remains consistent when the height of the shaft does not exceed 20 m. Once the shaft height reaches 50 m, the temperature of the smoke upstream of the fire decreases with the increase in shaft height. Simultaneously, the smoke downstream of the fire can be completely discharged through the shaft. As the shaft height increases in the deeply buried tunnel, the degree of plug-holing increases, leading to reduced smoke evacuation efficiency. This phenomenon is caused by the horizontal inertia force and vertical thermal buoyancy of the smoke below the shaft. The critical plugging phenomenon occurs when Ri = 2.72, as determined through force analysis of the smoke. Subsequently, we analyze the mechanism by which shaft height and heat release rate influence plug hole height and establish a quantitative expression equation for plug-holing height.