Deformation behaviors and failure mechanism of segmental RC lining under unloading condition

摘要

A shield tunnel lining structure is a type of complex structure system, and few systematic studies have been performed on its transverse deformation response under upper unloading conditions. In this paper, a sophisticated numerical model of segmental rings considering rebars, bolts, sealing grooves and caulking grooves was built to analyze the transverse deformation response of shield tunnels under upper unloading conditions. The failure mechanism of the segmental ring was studied based on the plastic hinge theory, and the controlling index of convergence deformation was proposed for engineering applications. Meanwhile, the structural response and failure process of the segmental ring under unloading were compared with those under continuous loading conditions. The results show that with the decrease in load, the tunnel deformation mode changes from the horizontal ellipse to the vertical ellipse, and the maximum vertical convergence deformation of the segmental ring is 46.3 mm when the unloading ratio is 0.68. The bending moment and axial force of the segmental ring decreases, subsequently reverses and keeps increasing until the structure failure. Concrete cracks mainly appear on the waist, crown and invert of the shield tunnel and penetrate along the thickness and longitudinal directions. The plastic hinge successively forms at 73 degrees, 287 degrees,180 degrees, 8 degrees, and 352 degrees locations during unloading. The variation in the segmental ring stiffness under the overlying unloading condition first recovers and subsequently continues decreasing until structural failure.