Analysis of the Effects of Shallow Gas on a Shield Tunnel during Leakage: A Case Study from the Sutong River-Crossing GIL Utility Tunnel Project in China

Soil layers including shallow gas threaten underground structures. Considering the special geological conditions of the gas-bearing layers under the Yangtze River for the Sutong River-crossing unity tunnel project, a solid-liquid-gas coupled 3-D numerical model was established to consider two different gas pocket conditions (a single gas pocket and multiple random gas pockets), and the effects of shallow gas on the tunnel segment and the adjacent soils in the long-term process of gas leakage were analyzed and discussed. A brief discussion of the displacement results and a comparison of the stress results determined by simulation and the designed data indicated that as the maximum displacement is on the order of millimeters for both gas pocket conditions and the simulated maximum bending moment is less than the design value for the bending moment, the structure of the tunnel segment has remained in a safe state during the leakage of the gas pocket, and the normal operation of the tunnel segment is basically not affected by the leakage of the gas pocket.