Application of the longitudinal ventilation system in the underground interconnected infrastructure: Assessment of flow distribution and confluence ratio

Longitudinal ventilation is widely employed in underground interconnected infrastructure, where the characteristic of the ventilated flow is distinctly different from the “normal” tunnels with a single structure. In this paper, the characteristic and the distribution of the ventilated flow in the underground interconnected infrastructure with longitudinal ventilation is studied. A small-scale experiment was carried out, where the effect of pressure rises and the location of the jet fan was taken into account. Results show that the ventilated velocity in a specified tunnel section is affected by the jet fan in the local tunnel section and the interconnected tunnel sections. For two interconnected tunnel sections that confluent at the junction point, with an increasing pressure rise in a specified tunnel section, the ventilated velocity in the local tunnel section increases whereas the ventilated velocity in another tunnel section decreases. The flow direction can even reverse to the opposite direction when the pressure rise of one tunnel section is large enough. To assess the variation of ventilated flow, the parameter of confluence ratio is defined and the prediction is established based on the theory of ventilation network, which can well describe the variation trend of the ventilation flow among different tunnel sections.