Abstract: The shallow deposited methine gas poses potential risk hazards to the underground structures. The controlled emission of the natural gas is one of the major measures to minimize the potential hazards during the underground structure construction. Further measures during the construction and the operation of the construction and operation of the underground structures include the improving ventilation and natural gas emission monitoring. This paper presents a case history of the Jingjiang Changjiang River crossing tunnel in Jiangying City. The theoretical analysis, insitu experiments and natural gas tests were applied in this project, along with the application of modified cone penetration testing (CPT) in order to characterization the vertical and horizontal distribution, components, pressure and quantities of the natural gas within the project limits. The impact of the natural gas deposition on the construction of the shielded river crossing tunnel is discussed and the risk management measures are proposed for the design and construction purposes.

Key words: tunnel projects, geotechnical investigation methods, shallow deposited gas, deposition characteristics, pressure and quantity of natural gas