Mechanical Model for Joints of Immersed Tunnel Considering the Influence of Joint Differential Settlement

Abstract

Immersed tunnels are generally connected by tube elements through the joints, which are the weakest parts and sensitive to deformation. However, it is inevitable that there will be vertical differential settlement between the joints of the tube element, resulting from uneven loads caused by back silting, differential settlement of foundations in soft soil, the heavy deposit of ground soil, and increasing tube length. Differential settlement at joints is very harmful to the safety of tunnel construction and operation, but the elastic foundation beam method—which is now widely used for calculation of settlement for immersed tunnels—cannot take joint differential settlement into account. Therefore, this paper proposes a new mechanical model for joints of immersed tunnels in consideration of the influence of joint differential settlement. The model is not only convenient for adoption in calculation, but also considers the influence of variation on the rigidity of groundwork. The results show that the bending stiffness of the joint changes with variations in differential settlement, and depends on whether differential settlement and the eccentricity are on the same side of the neutral axis or the other. Then, both the increase of eccentricity and the use of shear key will expose positive effect on the rise of bending stiffness. By calculating this mechanical model via considering differential settlement, the max error was only 7.3%. Therefore, it may have significance as safety guidelines for the construction and operation of immersed tunnels.