Experimental study on smoke movement characteristics and temperature distribution in high geothermal tunnel fire during construction with shaft structures

With the growing scale of construction tunnels in areas with complex geological conditions, the fire risk in this tunnels cannot be ignored and its control is facing the challenge of complex environments such as high geothermal hazards. In this work, a series of tests were conducted to investigate the smoke movement and temperature distribution in construction tunnel fire under the geothermal condition and natural ventilation through shafts. Results show that the air is heated by the high-temperature walls, which forms thermal airflow and an initial temperature field within the tunnel, resulting in the accelerated smoke spread. The construction shaft can mitigate the effect of geothermal environment and restrict the smoke movement. The maximum smoke temperature rise of the fire located in the geothermal area is affected by the geothermal temperature and a corrected prediction model is established. The smoke temperature distribution along the tunnel can be divided into three regions based on the fire source and construction shaft. With the increasing geothermal temperature, the overall smoke temperature rise increases and the temperature attenuation rate decreases. However, only smoke temperature rise at the downstream of the shaft drops rapidly with the increasing shaft height. Furthermore, exponential function formulas are established to describe the smoke temperature distribution. This study can provide references for risk identification and resilience improvement of tunnels during construction in complex natural environments.