Evaluating Respirable Dust Distribution in Tunnel Construction Works

This study investigates the generation and control of respirable dust in underground construction in Austria, motivated by the recent lowering of the permissible concentration limit for respirable crystalline silica. On site measurements of A dust concentrations and analyses of quartz content in tunnel dust samples showed that blasting and scaling generated the highest levels of respirable dust, with scaling yielding the highest quartz content. These data, which are influenced by local geological conditions, were used to validate the particle based simulations conducted in this work. Longitudinal ventilation systems in four Austrian tunnels were analyzed using computational fluid dynamics (CFD). Airflow simulations were validated against in situ velocity measurements and showed good agreement with the field data. For one representative tunnel, detailed particle dispersion simulations were performed using Lagrangian particle tracking approach and verified against measured dust concentration time series following tunnel blasting, confirming the capability of the CFD model to predict both airflow distribution and particle dispersion during tunnel construction. Several ventilation scenarios, including variations in duct¿face distance and duct outlet velocity, were evaluated. In most cases, the results indicate that current ventilation configurations are insufficient to maintain respirable dust concentrations below the updated permissable limits. Specifically, commonly used duct¿face distances are too large to ensure effective particle removal. Reducing the duct¿face distance to approximately five times the equivalent tunnel diameter (5D) significantly improves dust extraction; however, adequate control also requires sufficiently high duct outlet velocities to transport particle loaded airflow toward the outlet. Overall, this study demonstrates that compliance with the updated Austrian respirable silica standards requires both shorter duct¿face distances and increased ventilation airflow rates. The measured A dust concentrations and quartz content provided essential validation for the particle based CFD simulations, which in turn offer a robust tool for optimizing ventilation design in future underground construction projects.