Energy consumption and dilution of toxic gases in underground infrastructures: A case study in a railway tunnel under forced ventilation

Abstract

Toxic fumes are released after blasting in underground excavations. The analysis of safe re-entry times into the work areas is essential for addressing safety and productivity concerns. In this paper, a railway tunnel 2.1 km long under forced ventilation system is selected as a case study to assess the energy consumption and re-entry times after blasting under different ventilation conditions. First, three-dimensional CFD numerical models were conducted in order to predict the migration time to reduce the levels of noxious gases below the limits established in safety regulations. Field measurements were conducted to verify the accuracy of the results obtained in the simulations. Then, additional analytical models were conducted to evaluate the energy consumed by the ventilation system. The results obtained show that the accumulated re-entry time reaches 414 h for the excavation of the tunnel employing an airflow rate of 40 m3 s−1. This time increases by 33 % when the airflow rate decreases to 30 m3 s−1. However, even though the time decreases when the ventilation volume increases, energy consumption increases significantly, reaching 1,306 MWh for a ventilation volume of 40 m3 s−1 compared to 551 MWh using an airflow of 30 m3 s−1.