在公路隧道建设过程中，施工机械产生的废气以及从隧道围岩渗漏出来的有毒有害气体会对施工安全造成一定的影响。针对米仓山公路隧道巷道式通风系统横通道附近瓦斯不能及时排出的问题，通过CFD数值模拟对横通道附近空气流动和危险气体的扩散规律进行研究。结果表明： 沿横通道向掌子面方向的部分区域存在风速小于0.5 m/s的危险区域。为达到消除危险区域的目的，提出增大隧道进口风速、增大风管出口风速和增设射流风机3种方法对横通道附近流场进行优化。通过对比分析发现： 增设射流风机是消除危险区域最有效的措施，并且当在进风隧道横通道前方50 m处设置射流风机时，可使得整个隧道中不存在危险区域。

During the construction of highway tunnel, the gas produced by the construction machinery and the poisonous gas outburst from the surrounding rocks of the tunnel will have potential influence on tunnel construction safety. During the construction of Micangshan Highway Tunnel, the gas near the cross passage can not be discharged timely by gallery ventilation system, as a result, the air flow and the gas diffusion rules are studied by CFD numerical simulation method. The study results show that there is a "dead zone" ahead of the cross passage which has a much lower air velocity less than 0.5 m/s. In order to optimize the flow field near the cross passage and eliminate the "dead zone", optimizations are carried out on flow field near cross passage in terms of increasing the inlet air velocity of tunnel entrance and outlet air velocity of air duct and adding jet fan. The comparison results show that the method of adding jet fan is the optimum. The "dead zone" will be eliminated by setting jet fan 50 m ahead of cross passage.