Theoretical Analyses of the Stability of Excavation Face of Shield Tunnel in Lanzhou Metro Crossing beneath the Yellow River

Abstract

Based on an actual engineering case, this study focused on the limit support pressure, instability mechanism, and instability failure mode of the excavation face in the sand pebble stratum when crossing below the Yellow River. First, PFC3D was used to investigate the instability mechanism and failure mode of the excavation face in the sand pebble stratum. Then, the Terzaghi loose earth pressure formula was reasonably modified, and the limit support pressure was derived using this modified formula and the limit equilibrium mechanics model. Finally, the result was compared with those of an indoor test and a numerical simulation. The research showed that the calculation method proposed in this study was more suitable for underwater shield tunnels and formations where the soil arching effect is evident. The support pressure had a significant influence on the instability failure mode, whereas the influence of the buried depth was small. The limit support pressure decreased with an increase in the internal friction angle, a decrease in the water cover depth, or a decrease in the angle between the maximum principal stress direction and the horizontal direction.