Abstract: In case of fire,  the smoke is discharged by its thermal buoyancy for shallowburied urban road tunnels with vertical shafts,  but the actual smoke exhaust situation remains unclear. To examine the smoke diffusion characteristics of the tunnel main body and the smoke exhaust performance of the shaft in summer,  three 1.58 ×1.58 m2 diesel fire experiments with different ignition points were conducted in two tunnels in Nanjing in 2019,  where the smoke parameters under the ceiling and at the top/bottom of several shafts are measured. It was found that the shafts near the fire source had substantial smoke exhaust,  with a maximum smoke exhaust temperature of 47 ℃,  a speed of 5 m/s,  and a CO volume fraction of 18×10-4 ,  whereas shafts far from the fire source had substantial backward smoke flow. The following are the results of the analysis: (1) The longitudinal temperature/velocity distribution of smoke flow under the ceiling obeys the law of power exponent attenuation,  and the attenuation coefficient is significantly influenced by the season,  the ignition position,  the upstream,  and the downstream. (2) The measured smoke exhaust of the shaft decreases gradually as the distance from the fire source increases,  and the existing prediction models for smoke exhaust does not consider the backward flow and uneven distribution of smoke. (3) The 〖WT5BX〗Ri′〖WT５《TNR》〗 number of the #6 shaft in the Shuiximen tunnel reaches 10.8 (Test 1) and 1.5 (Test 2),  respectively,  and the existing model with 〖WT〗Ri′c〖WT５《TNR》〗=1.4 is unsuitable for evaluating the smoke flow state at the bottom of the shaft.

Key words:  , fire condition in summer, urban road tunnel, vertical shaft, natural smoke exhaust, field experiment, temperature, exhaust smoke volume