Study on Regularity of Gas Emission and Diffusion at Tunnel Face during Tunnel Construction

In order to ascertain the generating principle of gas accumulation and the rules of ventilation flow field of tunnel face,gas emission and diffusion during the process of tunnel construction,the 3D numerical calculation models of forced ventilation are established to study the impact of gas emission quantity,air quantity and air duct positions on gas diffusion. The result shows that( 1) the large gradient change of gas concentration is in backflow zone and the phenomenon of gas accumulation appears near the gas emission face,however,the gas concentration tends to be uniform with the distance from gas emission face increasing;( 2) the lager the gas emission,the greater the effect on the flow field and the broader the scope of whirlpool,and the whirlpool has a retention effect on the gas emission;( 3) Increasing the ventilation quantity can effectively control gas accumulation,but the arrangement of air duct positions exerts larger impact on the gas accumulation only within a certain range of positions.