浅层有害气体成藏特征对隧道施工的影响

地下浅层有害气体是影响地下交通工程施工与后期运营的重要危险因素,对其地质成藏特征的研究可有效指导治理措施的设计部署。本文以昆明地铁2号线工程为例,通过对工程中有害气体喷发重点区段现场勘察与实验分析,研究分析了浅层有害气体成藏特征。该工程区段地下浅层有害气体是赋存于第四系泥炭质土层中以甲烷组分为主的小型、低压生物气。含气层空间分布特征显示,福保路段揭露两层含气层中的下部含气层与地铁结构线为纵贯关系,施工危险性较大；而该段上部含气层以及官南路段含气层均不与地铁结构线交叉,危险性较小。尽管由于前期工程施工导致勘察区段地下有害气体压力与流量降低,但不排除勘察区间或周边存在小型高压气体聚集区的可能性,故建议在施工过程中要对地下有害气体进行同步探测,对于高压气层采取提前排气与压入式机械通风处理措施,同时加强现场有害气体监测。

Study on characteristics of shallow harmful gas accumulation and its influence on subway tunnel construction

The shallow underground harmful gas is an important risk factor affecting the construction and later operation of underground transportation projects. The study of its accumulation characteristics can effectively guide the design and deployment of treatment measures. This paper takes Kunming Metro Line 2 project as an example, and analyzes the characteristics of shallow harmful gas accumulation through field survey and experimental analysis of the key sections of harmful gas eruption in the project. The harmful gas in the shallow underground layer of the project section is a small, low-pressure biogas mainly composed of methane that occurs in the Quaternary peaty soil layer. The spatial distribution characteristics of the gas-bearing zone show that the lower gas-bearing zone of the two gas-bearing zones in the Fubao section is longitudinally connected to the subway structure line, and the construction risk is greater; while the upper gas-bearing zone of this section and the Guannan section contain the gas layer does not cross the subway structure line, and the danger is small. Although the pressure and flow rate of the underground hazardous gas in the survey section have been reduced due to the preliminary construction, the possibility of small high-pressure gas accumulation areas in the survey area or the surrounding area is not ruled out. Therefore, it is recommended that the underground hazardous gas be detected simultaneously during the construction process. The high-pressure gas layer adopts pre-exhaust and press-in mechanical ventilation treatment measures, and at the same time strengthens on-site harmful gas monitoring.