Mixed ventilation approach combined with single-shaft complementary system for highway tunnels

Abstract

Highway tunnel ventilation systems are associated with high civil construction and operation costs, as well as large differences in the total required air volume for uphill and downhill tunnels. Thus, in the current study, a complementary ventilation system is applied to the shaft segmented longitudinal ventilation mode to form the mixed ventilation mode of the complementary combined ventilation shaft. The mixed ventilation formula is derived based on the tunnel ventilation theory. Combined with the design process of tunnel ventilation, the design process from the location of the ventilation shaft, design air volume, the air interchange channel location, the air exchange ratio of air interchange channel to pollutant concentration is determined, and the mixed ventilation mode conditions are analyzed. Moreover, an engineering example is employed to analyze the mixed ventilation, and to compare the traffic wind utilization rate, operation energy consumption and the civil construction scale between conventional segmented longitudinal ventilation and mixed ventilation. The results reveal that compared with the conventional segmented longitudinal ventilation mode, the mixed ventilation mode effectively improves the utilization rate of traffic wind, reduces the adverse effect of surplus traffic wind pressure on tunnel ventilation and minimizes mechanical power usage. In terms of operating energy consumption, taking a vehicle speed of 60 km/h as an example, the mixed ventilation method fully utilizes the traffic wind pressure in the tunnel. Although it is necessary to turn on the jet fan in the tunnel to increase the power, the energy consumption of the axial flow fan is reduced by 31.9 %, and the total power is reduced by 9.5 %, greatly lowering the energy consumption of the tunnel operation. Despite the addition of the traverse ventilation channels by the mixed ventilation method, reductions are observed in the construction of a ventilation shaft, the connecting channels, the overall ventilation civil engineering volume, and the initial civil construction investment cost. Moreover, the mixed ventilation method includes a smoke exhaust channel, thus solving the smoke exhaust problem of tunnel fires.