Numerical Simulation Study of Shield Tunnel Construction Under Canal in Water-Rich Sand Layer

Abstract Focusing on the impact of tunnel shield construction on the surface and surrounding environment in water-rich sand layers beneath a canal in the paper, based on indoor geotechnical experiments, the FLAC3D method is used to establish the numerical model for the shield construction of the Nantong City Metro Line 1 in Jiangsu Province, passing through the water-rich sand layer beneath the Tonglv Canal. The study explores the effects of shield tunneling on the surface and surrounding environment through numerical simulation, thereby guiding in-site construction. The simulation results indicated that there is no significant difference in the surface settlement values between single-line and double-line synchronous tunneling, but in general, the latter has a larger surface settlement and strata deformation. The thrust force at the tunnel face of the shield construction significantly disturbs the deformation of the strata, and excessive or insufficient thrust force can lead to bulging deformation of the soil in front of the excavation face. The excavation surface and the soil behind it will be affected by the thrust of the palm face to produce extrusion deformation in the opposite direction to the digging direction, and extrusion deformation may occur with the increase of the thrust force. Therefore, the palm surface thrust should be slightly larger than the value of the static soil pressure and should be adjusted timely according to the construction section of the shield tunneling. It is recommended to adjust the grouting pressure to about 0.2 MPa when passing through the middle of the canals on both sides of the water-dividing island and to appropriately increase it when passing through the water-dividing island or the riverbank. The research results provide a reference value for the application of the earth pressure balance shield tunneling method in the construction of water-rich sand layers.