Experimental studies on the smoke extraction performance by natural ventilation with a board-coupled shaft in a deep buried tunnel

Abstract

In theory, if the plug-holing phenomenon can be effectively eliminated, the application of natural ventilation with vertical shaft will no longer be limited to shallow buried tunnels, or even extended to deep buried tunnels. Researches have validated that the board-coupled shaft (BCS) can efficiently eliminate the plug-holing phenomenon and promote the smoke extraction performance in a shallow buried tunnel. The purpose of this paper is to explore whether the BCS is effective and has stable smoke extraction performance in deep buried tunnels. Experiments were conducted in a 1/20 scale model tunnel, and the height of the board-coupled shaft applied in this study is 5 times the height of the tunnel height. The influence of heat release rate (HRR) and board location on the smoke extraction performance was investigated. Experimental results indicated that the BCS is effective and has stable smoke extraction performance for the deep buried tunnel applied in this study. Besides, it can be found that the smoke extraction efficiency of the BCS will be improved and the improvement in the smoke extraction performance with BCS is stable when the power of the fire source increases. Also, the optimal board location for the BCS to achieve the peak smoke extraction performance was obtained and the peak smoke extraction performance of the BCS is about 1.451–1.457 times of the traditional shaft. Beyond that, two dimensionless correlations were developed under the general condition that the first shaft cannot extract the entirety of the smoke, one is the correlation function for analyzing the smoke temperature difference and the CO concentration in the shaft; the other is the correlation for predicting the dimensionless volume flow rate under different HRRs and board locations. These studies may contribute positive significance for promoting the application of natural ventilation with vertical shafts.