Numerical and experimental investigation of air flow behavior and H2S gas emission through an inclined traversed tunnel

This paper numerically and experimentally studies the air flow at the intersection of the main and sloping access tunnels of the long Zagros tunnel, in which H 2 S gas is one of the main pollutants produced during the excavation. The aim is to investigate the effect of length and slope of the access tunnel as well as inlet air flow rate on the distribution of H 2 S concentration at the intersection and access tunnel. The experimental study is performed by field measurement of the velocity and concentration of H 2 S in the air flow through the access tunnel. For this purpose, air velocity and concentration values are determined at different points of several sections of the access tunnel using measuring devices. In order to increase the accuracy of field measurements and ensure its results, air velocity and H 2 S concentration within the access tunnel are measured in several stages and at different time intervals. The numerical analysis is performed by three-dimensional simulations of incompressible steady turbulent flow in the tunnel, and the results are compared with the experimental ones. The results show that the concentration of H 2 S gas inside the access tunnel has the gradient and the concentration of hazardous gas decreases in the direction of the access tunnel toward the tunnel exit. Moreover, increasing the slope of the access tunnel enhances the intensity of gas concentration in the regions near the bottom of the access tunnel and the uniformity of the gas mixture along it toward the outlet. Increasing the fresh air flow rate in the tunnel heading face promotes the flow velocity and decreases the gas concentration inside the tunnel, but it does not change the H 2 S distribution in different cross sections of the access tunnel. Moreover, increasing the length of the access tunnel also contributes to the uniformity of air–H 2 S mixture.