Study on the Influence of Tunnel Slopes on Smoke Spread Characteristics and Critical Velocity
The"chimney effect"caused by the long longitudinal slope of the tunnel makes fire smoke control more difficult.To investigate the influence of tunnel gradient on the smoke spreading law,a combination of numerical simulation and theoretical analysis was used to investigate the influence of tunnel slope on smoke spreading,and a critical wind speed calculation model applicable to sloping tunnels was established.Research shows that:1)The lower slope of the smoke spread is more important than the higher side of the smoke propagation.2)The steady flow rate of the smoke on the higher side of the vault is quadratically related to the tunnel slope.3)The maximum temperature rise curves in the tunnel without slope and in the tunnel with one-side slope have different trends.The temperature first rises rapidly and then tends to be a straight line for no sloping tunnels.For sloping tunnels,the temperature first rises and then decreases with time,and finally tends to be stable gradually.4)About 30 m from the fire source is the critical distance for the change of the visibility distribution law in the tunnel cross-section.The greater the slope,the higher the minimum visibility at the characteristic height of 2 m.5)The critical velocity correction coefficient for sloping tunnels is proposed,and the critical velocity calculation model applicable to sloping tunnels is established.Smoke control measures for different fire sizes are given.
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