Stability Analysis of Shield Excavation Face Based on Particle Flow in Different Depths of Sandy Gravel Stratum

The objective of this work was to study the minimum support force of the shield excavation face of sand‐gravel stratum. Based on the geological conditions obtained from the exploration of the 18th line of the Chengdu Rail Transit and the shield excavation parameters obtained from excavation, particle flow DEM PFC3D and FLAC3D were used as tools; the digital triaxial compression test was performed to calibrate the mesoscopic parameters of the soil; numerical excavation models were built for deep‐buried and shallow‐buried sand and gravel stratum shield tunnels; surface settlement and minimum support force under different depths and different supporting forces were obtained in the end. The stability of the excavation face under the condition of 10 kPa∼60 kPa support force was analyzed; the excavation surface gradually tended to stabilize, and the surface subsidence decreased with the increase of support force. When the supporting force was greater than or equal to 3 kPa, the excavation surface was stable and the surface settlement speed gradually decreased to zero with time. While analyzing the stability of the excavation face of 5 m, 10 m, and 15 m buried deep gravel tunnels and the influence of the support force on the surface settlement, the minimum support force that did not consider the surface settlement was reduced and the minimum support force required to control the surface settlement was increased as the tunnel depth decreased. Using this method, the depth of the excavation sand‐gravel tunnel and the support of the excavation face could be obtained to meet the requirements of surface subsidence control and the economic benefits of the project could be improved.