Study on thermal pressure in a sloping underground tunnel under natural ventilation

Tunnels are of key importance to the ventilation network in underground buildings. For sloping tunnels, the effect of thermal pressure on the underground ventilation system has not been clarified in the existing research. A field test in an underground sloping tunnel was carried out and the results showed that the temperature decreases in the form of exponent. Based on an exponential model of temperature decrease, an equation to predict thermal pressure is proposed for sloping underground tunnels. Four factors on the thermal pressure, surface roughness of the tunnel wall, air velocity, dimensions of the underground tunnel and temperature difference between the air and the tunnel wall are discussed in detail. Surface roughness of the tunnel wall, air velocity and dimensions of the tunnel have been found having little impact on the thermal pressure efficiency when the tunnel is beyond the length of Lmin. The temperature difference between the air and the tunnel wall is the main factor on the thermal pressure efficiency. A simplified method is recommended to calculate the thermal pressure for sloping underground tunnels.