Three-dimensional investigation of how newly constructed buildings supported on raft foundations affect pre-existing tunnels

Abstract

Abstract In densely populated areas, there is increasing construction of high-rise buildings adjacent to existing tunnels. The interactions involved are complex. Based on experience and field monitoring, many tunnel owners impose exclusion zones for construction close to their tunnels. This paper studies the effect of a newly constructed building supported by a raft foundation on an intact pre-existing tunnel. With the aid of PLAXIS software, a detailed three-dimensional finite element analysis is used to conduct a parametric study showing the interaction between the burial location of the pre-existing tunnel and the new raft foundation. The intact concrete lining is modelled by using the newly developed concrete model included in the PLAXIS user-defined library. The model considers the non-linearity of the material behaviour and the distinction between the concrete strength in tension and compression. The soil medium where the tunnel system is constructed is simulated by using a hardening soil model with small-strain stiffness, which accounts for increased stiffness at small strains. The construction of the tunnel is divided into several phases, where each phase is simulated with the advancement of the shield boring machine. Accordingly, new design guidelines can be developed for raft foundations in close proximity to pre-existing tunnels.