Risk Analysis of the Opening of Shield-Tunnel Circumferential Joints Induced by Adjacent Deep Excavation

Abstract

Deep excavation projects in urban areas may adversely affect underlying tunnels. Differential settlement and additional stresses in existing tunnels occur frequently due to excavation construction, which leads to the opening of circumferential joints or even to water leakage. To ensure the security of existing tunnels under deep excavation during construction, this paper proposes a risk assessment methodology that aims to evaluate the risks of circumferential cracks of preexisting shield tunnels. Existing tunnels are assumed to be a beam on a Winkler elastic foundation. The longitudinal deformations of the tunnel and internal forces in tunnel structures are obtained from the singular function method. Based on the equivalent axial stiffness theory, the relationship between the opening of circumferential joints and the additional bending moment is established. The Monte Carlo simulation technique is used to quantitatively estimate the potential risk levels of circumferential joints. The calculated results are verified by in situ observations.