城市顶管覆土浅，周边管线分布密集且临近顶管。顶管施工过程中由于各种因素可能导致燃气管线的断裂和燃气泄漏，致使以瓦斯为主的燃气在土体中不断扩散并进入顶管内，给顶管安全施工带来了潜在的极大危害。以毛家湾污水处理厂进厂干管项目为背景，采用理论分析、数值计算等方法对瓦斯在土体和顶管中的扩散机理以及施工通风技术开展深入研究。研究结果表明：随着时间的增长，瓦斯在土体中的扩散通量先增大后趋于稳定；顶管离泄漏孔越远，掌子面瓦斯涌出量越低，瓦斯扩散至顶管所需时间越长；顶管内掌子面附近风管对侧瓦斯浓度相对较高，瓦斯容易聚集；随着风管送风量的增加，掌子面附近产生了较强的空气流动，掌子面附近瓦斯浓度不断降低，但瓦斯浓度降低速率有所减小，在风管送风量为131 m³/min时，顶管内最高瓦斯浓度为4.57%，已低于瓦斯爆炸下限；随着风管风口至掌子面距离的增加，顶管内最高瓦斯浓度先减小后增大，在风管风口距离掌子面4 m时，顶管内最高瓦斯浓度达到最小值为4.41%。基于此，本文提出了较为合理的顶管施工通风参数。

The soil covering of urban pipe jacking is shallow, and the surrounding pipelines are densely distributed and close to pipe jacking. In the process of pipe jacking construction, various factors may lead to gas pipeline fracture and gas leakage, resulting in gas, mainly gas, spreading in the soil and entering the pipe jacking, which brings potential great harm to the safety of pipe jacking construction. Based on the main-pipeline project of Maojiawan sewage treatment plant, the diffusion mechanism of gas in soil and pipe jacking and the construction ventilation technology were studied by theoretical analysis and numerical calculation. The results show as follows. With the increase of time, the diffusion flux of gas in soil first increases and then becomes stable. The farther away the pipe jacking is from the leakage hole, the lower the gas emission amount on the face, and the longer the time required for gas diffusion to the pipe jacking. The gas concentration on the opposite side of the air duct near the face of the pipe jacking is relatively high, and the gas is easy to gather. With the increase of air supply volume in the air duct, strong air flow is generated near the face, and the gas concentration near the face continues to decrease, but the rate of gas concentration reduction decreases. When the air supply volume in the air duct is 131 m³/min, the highest gas concentration in the pipe jacking is 4.57%, which is lower than the lower limit of gas explosion. With the increase of the distance between the air duct tuyere and the face, the maximum gas concentration in the pipe jacking first decreases and then increases. When the distance between the air duct tuyere and the face is 4 m, the maximum gas concentration in the pipe jacking reaches the minimum value of 4.41%. Based on this, a more reasonable ventilation parameter for pipe jacking construction is proposed.