Additional Stress of Soil and Surface Settlement during Tunnel Shield Construction

To study the influence of shield excavation on the surrounding soil, and to control the influence of the shield excavation of the subway tunnel on the surface settlement and the deformation of the surrounding buildings, it is necessary to study the additional stress of the surrounding soil caused by the tunnel shield excavation and the law of surface settlement. Combined with a shield construction project of a subway tunnel, this article uses the Mindlin solution in elastic mechanics to obtain three-dimensional calculation formulas for the additional thrust on the shield cutter head surface and the additional stress and displacement field caused by the friction force between the shield shell and the soil contact interface on the surrounding soil. The Loganathan ground movement pattern is used to determine the soil movement mode. The source–sink method is used to study the formula for calculating the three-dimensional additional stress of the soil around the shield tunnel caused by ground loss. The results show that when the shield is digging, the ground goes through five stages, namely the uplift of the ground before the arrival of the shield cutter head, surface settlement when the shield reaches the surface subsides when the shield tail of the shield passes through, the passage of the shield tail of the shield, surface settlement when the lining is separated from the shield, and consolidation and settlement after the shield passes through.