Investigation on overburden thickness considering face and anti-floating stability of shallow shield tunnel

Ensuring the safety of water-rich shield tunnels requires a reasonable design of overburden thickness. However, few studies have comprehensively investigated the design of overburden thickness for shield tunnels in terms of both face and anti-floating stability. In this study, the traditional wedge-prism model was optimized, and formulas for active and passive limit support pressure of tunnel faces were derived for various excavation inclination angle and seepage conditions. The analytical solution for two limit support pressures, with special attention on the proposed passive failure model were verified using finite element numerical simulations. Design procedures for a reasonable range of overburden thickness were provided based on the analytical solution of the uplift resistance and limit support pressure. The passive limit support pressure was found to increase with the cohesion and internal friction angle of soil stratum and decrease with the excavation inclination angle, while the active limit support pressure exhibited the opposite trend. The two limit support pressures increased with rising groundwater levels.