Safe excavation of large section tunnels with Earth Pressure Balance Tunnel Boring Machine in gassy rock masses: The Sparvo tunnel case study

The paper describes the safety engineering system developed for the excavation of the Sparvo twin tunnels (Italy) with EPB-TBM. The machine (Herrenknecht S-574) was specifically designed to prevent the risk of having explosive gas-air mixtures and ignition sources in the same place and at the same time, hydraulically confining the volumes inside the machine. After a brief description of the case study, the paper illustrates the design criteria, the technological solutions adopted for the construction of the Herrenknecht S-574 and the operating procedures. Then, the paper focuses on examining and interpreting the methane monitoring results during Sparvo tunnel construction, that highlight the presence of huge volumes of methane. The developed safety engineering system allowed tunnelling without interruptions even with sensible gas flows. Current limits and possible improvements to the safety system described are also discussed.