Excavation Face Stability of Shield Tunneling Closely Under Existing Tunnels: Particle Flow Simulation

Abstract

When a new tunnel passes closely under an existing tunnel, it will induce ground subsidence and adversely affect the existing subway tunnel. Aiming at the construction form of shield passing closely under existing tunnel, a numerical model using two-dimensional particle flow was set up to study the failure form of the excavation face, the relationship between support force and excavation displacement, longitudinal deformation of the surface and the earth pressure distribution pattern around the existing tunnel. The results show that the support pressure of shield excavation face increases first and then decreases with the increase in excavation surface displacement due to the presence of existing tunnel. The maximum vertical settlement value of the ground surface appears in the range of 2D from the center of the existing tunnel. With the advance of shield tunnel, the earth pressure above the new tunnel segment increases gently. When away from the existing tunnel, the horizontal earth pressure above the tunnel increases gradually, and the earth pressure in the area ahead of the shield tunnel along the depth presents a significant nonlinear distribution. The research results can provide theoretical basis and early guidance for such construction in the future.