The Influence of Wall Roughness on the Ventilation Resistance Coefficient during Tunnel Construction Period

Understanding the resistance coefficient along the tunnel wall is helpful to optimize the ventilation design of tunnel construction and improve the rationality of ventilation scheme. The influence of the height, shape and spacing of rough elements on the resistance coefficient along the tunnel wall is studied. Through the model test and the numerical model, the difference between the empirical formula and the numerical simulation results was explored. The results show that: With the higher height of the rough element on the tunnel wall, the influence on the resistance coefficient along the tunnel wall is less. The shape of rough elements on the tunnel wall has a great influence on the resistance coefficient along the tunnel, and the semi-spherical rough elements have the smallest resistance coefficient along the way. Comparing the calculated results of empirical formula with the numerical simulation results, the difference between them is relatively stable, which is related to the height of rough elements. The correction coefficient α is proposed for the empirical formula, and the corresponding relationship between α and the average roughness height Δ of the wall is α=1.29+0.0248Δ.