Effects of geothermal temperature on smoke dynamics in construction tunnel fires

The development of traffic networks in mountainous areas has led to an increasing number of tunnels being constructed in regions of high geothermal activity. This study examined the effects of geothermal temperature, heat release rate, and fire source location on temperature distribution and smoke movement in construction tunnel fires through a series of scaled-down experiments. Results showed that geothermal conditions heat the air, creating layered flow within construction tunnels. The temperature and velocity of the induced airflow along the tunnel length were characterized. The upper airflow caused by geothermal conditions hinders the spread of smoke toward the tunnel face, resulting in a complex thermal stratification phenomenon. A model for predicting the smoke diffusion length upstream of the fire source was developed, considering geothermal temperature, heat release rate, and fire source location. Additionally, the ceiling temperature distribution was analyzed, showing that downstream temperature decay is insensitive to fire location, while upstream temperature decay can be divided into geothermal-affected and non-affected zones based on the fire source position. Prediction models for the ceiling temperature distribution upstream and downstream were established, respectively. These findings enhance the understanding of smoke dynamics in construction tunnel fires under high geothermal conditions.