Impact of fixed fire-fighting system on road tunnel structure

摘要

A fire in a road tunnel may pose a serious threat to the integrity of the tunnel structure. Temperatures at the surface could reach over 1200°C within minutes without a fixed fire-fighting system (FFFS). In this paper, the impact of the fixed fire-fighting system (also known as the fire suppression system) on the thermal load on the road tunnel structure was assessed with a simulated flammable liquid fire. Time-temperature curves were developed at the center of and away from the fire and compared against the RWS curve, the standard temperature curve for the structure to withstand. It was confirmed that the temperature of the tunnel structure might grow as fast as or even faster than the RWS curve in some cases at the fire site. However, the tunnel ventilation and FFFS systems had a significant impact on tunnel temperature. Once the FFFS and ventilation systems were activated, the temperature at the tunnel surface drastically decreased. It was found that the tunnel surface area exposed to high temperatures over 380°C was limited and exposure was only for a short duration. The affected surface area was promptly mitigated after the FFFS is activated. The resultant time-temperature curves were used for thermal integrity testing of concrete slab samples to determine spalling temperatures and structural integrity. Results of the CFD analysis were used to evaluate the area of high temperature exposure and are presented in the paper.