Abstract: The spacing between vertical shafts can change the pressure difference inside and outside the shaft. When the pressure difference inside and outside the shaft is zero, tunnel fire smoke cannot be discharged, and the corresponding position of the shaft is the critical spacing between vertical shafts. Based on the theoretical analysis of the pressure difference between the inner and outer openings of the vertical shaft, a theoretical model of the critical spacing of the vertical shaft is provided, and then FDS simulation is used for simulation verification. The results show that setting vertical shafts can significantly reduce tunnel temperature. When the distance between vertical shafts is a critical distance, the temperature drop is close to 150 ℃, and the temperature of personnel evacuation paths is below 60 ℃. The smoke exhaust efficiency of vertical shafts is between 55% and 80%, which can effectively carry out smoke exhaust in vertical shafts; When the distance between vertical shafts exceeds the critical distance, the smoke pressure inside the tunnel is less than the wind pressure at the outlet of the shaft, and the smoke exhaust efficiency of the shaft is less than 50%.

Key words: urban shallow buried tunnels, vertical shaft smoke exhaust, critical spacing model for vertical shafts, natural smoke exhaust