Geological environment problems during metro shield tunnelling in Shenzhen, China

Shenzhen has abundant river systems, intense tectonic activity and complex geological conditions. The depth of Quaternary deposits is thin and uneven, and the primary bedrock comprises granite with various degrees of weathering, which covers more than 50% of the area of Shenzhen. Karst strata have developed in the eastern part of Shenzhen, and there are five groups of fracture zones in the area. Shenzhen also has some problematic soils, including granite residual soil, and muddy clay and silt. Metro tunnels are constructed using the shield tunnelling method. In Shenzhen, different strata are encountered during metro shield tunnelling, including upper-soft and lower-hard strata, hard rock strata, soft–hard alternating strata, under-crossing river or reservoir strata, muddy clay and silt strata and granite residual soil strata. The various strata encountered during shield tunnelling may result in a series of problems with the geological environment. Environmental geological problems during tunnelling are different for different strata, among which the major issues include serious cutter wear, difficulty in controlling the trajectory of the shield machine, shield machine jam, roof fall and slurry spewing. Different countermeasures should be implemented according to the characteristics of the strata to ensure the safe construction of metro tunnels. In this study, a case study of the Shenzhen Metro Line 10 is introduced, where tunnels pass through three specific strata: hard rock strata, boulder strata and under-crossing reservoir strata. In the future, more engineering cases that pass through different strata can be summarized according to the tunnel construction project in Shenzhen.