Optimized ventilation design for high-geothermal tunnels considering worker comfort

In high-geothermal tunnels, extreme heat and humidity pose significant health risks to workers, making an optimized ventilation design crucial for improving worker comfort. A numerical model is developed to analyze the evolution of temperature and humidity within high-geothermal tunnels. A sensitivity analysis of the ventilation parameters is conducted using the wet-bulb globe temperature (WBGT) as an indicator. Field tests on worker comfort are performed, and changes in skin temperature and heart rate with the WBGT are determined. The response-surface methodology (RSM) is employed to optimize the tunnel-ventilation parameters. The results indicate that the airflow field of the tunnel is divided into three zones: jet, vortex, and recirculation. For a tunnel with an initial temperature of 80 degrees C and humidity of 60 %, temperatures near the tunnel wall remain above 35 degrees C, with humid air accumulating in this area after 7 h of ventilation. The distance between the ventilation outlet and tunnel face, wind speed, airflow temperature, and rock temperature significantly influence the spatiotemporal evolution of the WBGT. Monitoring revealed that the heart rates and skin temperatures of workers exceed normal levels in high-geothermal tunnels, with heart rates increasing linearly and skin temperatures increasing exponentially with the WBGT. Response-surface analysis identified the ventilation-flow rate, temperature, and duration as key factors affecting the WBGT. Tunnels with rock temperatures of 80 degrees C require additional cooling measures when ventilation outlet temperatures exceed 20 degrees C. The research findings are of great significance in mitigating health risks to workers arising from the adverse conditions of high-geothermal tunnel environments and in ensuring safe tunnel-construction practices.