Study on Risks and Countermeasures of Shallow Biogas during Construction of Metro Tunnels by Shield Boring Machine

Abstract

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.

Case Study of the Largest Concrete Earth Pressure Balance Pipe-Jacking Project in the World

“…During jacking under water, there are possible combustible biological gases embedded into the rotten materials in the underwater shallow ground (20). The shallow biogas may penetrate the pipeline from the joints of the segmental lining, the head and the shield tail of the jacking machine, which could result in casualties and property loss (21)(22)(23)(24).…”

A Study of the Segment Assembly Error and Quality Control Standard of Special-Shaped Shield Tunnels

“…It is difficult to obtain the error parameters in the assembly of a shield tunnel [31]. The data from the construction party is often collected after the assembly [32], which generally includes the data after the segment is out of the shield tail and the deformation is stable.…”

Research on the dismantling of double-arch tunnel after long-term service—the case study of Huangmeishan Tunnel demolition project

“…The demolition project poses higher risks compared to tunnel construction due to three key aspects. Firstly, the complexity of geological formations makes it difficult to ensure the safety of tunnel construction (Jiang et al, 2021). The surrounding rock of the tunnel has already been disturbed during the construction of the existing tunnel, which will be further disturbed during the demolition process (Bai et al, 2022).…”