An Outlook for Researches on the Impact and Control Technology of Shield Construction in Gassy Soils

Gassy soils will be inevitably encountered in the shield construction, and shallow gas in gassy soils can have a huge impact on the shield construction process and pose serious hazards to construction workers. After summarizing the types of gassy soils, the pressure of shallow gas, the buried depth and gas composition in various regions of China, it is found that most are dominated by CH4 gas generated by the decomposition of organic matters,with slightly different causes. Based on analysis on existing disaster cases, it illustrates the engineering influence of shallow gas in gassy soils, the impact of controlled gas release, and the influence of matric suction. The results show that gassy soil is a special unsaturated soil, and its shear strength and soil deformation are influenced by the matric suction. At the same time, the uncontrolled or controlled release of shallow gas will cause different degrees of disturbance to the surrounding soils, while the engineering solutions are mostly based on pre-controlled gas release. Some effective measures are presented, which can eliminate the hidden hazards of harmful gas in gassy soils to the construction of subway tunnels.