With the intensive development of cities, the utilization of underground space has attracted more and more attention from industry and academia. Underground rail (metro) in cities has become an imperative mode for people in their daily lives. Meanwhile, the safety of rail tunnel construction has constantly been a challenging issue because of the presence of complex strata containing shallow biogas. Accidents in tunnel construction because of shallow biogas which resulted in massive casualties and property loss have been reported in some recent literature. The excavation of formations containing shallow biogas not only poses a threat to the safety of the earlier stage of tunnel construction but also affects the later operation of metro lines. Therefore, the safety problem caused by shallow biogas should be taken into consideration seriously and avoided in the pre-construction stage. A typical underwater metro tunnel, Hangzhou Metro Line 6, is introduced in this study to suggest the proper approach to deal with the biogas problem during the construction process. The generation mechanism of shallow biogas is clarified and the process of identifying biogas risk during strata exploration is also discussed. A risk identification and control system for shield tunneling through biogas strata is proposed to mitigate the potential dangers of shallow biogas during the construction process. This study provides actual construction experience and countermeasures for other similar metro tunnel projects that encounter biogas strata to diminish the potential risks and avoid severe accidents.

随着城市的集约化发展，地下空间的利用已引起工业界和学术界的越来越多的关注。城市地下铁路（地铁）已成为人们日常生活中的必不可少的模式。同时，由于包含浅沼气的复杂地层的存在，铁路隧道建设的安全一直是一个具有挑战性的问题。最近的一些文献报道了由于沼气浅而造成大量人员伤亡和财产损失的隧道施工事故。含有浅沼气的地层的开挖不仅对隧道施工初期的安全性构成威胁，而且还影响地铁线路的后期运营。所以，在施工前阶段，应认真考虑浅沼气引起的安全问题，避免此类问题的发生。本研究介绍了典型的水下地铁隧道，杭州地铁6号线，以提出在施工过程中处理沼气问题的正确方法。阐明了浅层沼气的产生机理，探讨了地层勘探过程中沼气风险识别过程。为了减轻施工过程中浅层沼气的潜在危险，提出了一种通过沼气层进行盾构隧道掘进的风险识别和控制系统。该研究为遇到沼气地层以减少潜在风险并避免严重事故的其他类似地铁隧道项目提供了实际的施工经验和对策。