Three-dimensional numerical simulation of pile-twin tunnels interaction – Case of the Shiraz subway line

Abstract

The use of an underground transportation network to solve urban traffic problems is a practical solution. Shiraz, one of the most famous touristic cities of Iran, is developing its own urban railway network using mechanized twin tunnels. It is almost inevitable for tunnels to pass nearby an existing pile foundations. In this study, a three-dimensional numerical model was developed to investigate the pile-tunnel interaction. All the mechanized excavation phases of an EPB-TBM (Earth pressure balance, Tunnel boring machine) and the segmental lining were modeled using a finite difference code. The role of the Constitutive soil’s model is also investigated by using both a linear elastic-perfectly plastic one (failure criteria of Mohr-Coulomb type) named as MC and a nonlinear perfectly plastic one the Cap-Yield (CYsoil) constitutive model. Two different scenarios were considered: the influence of tunneling on existing piles and the impact of installing bridge piles nearby existing twin tunnels. The influence of the soil/structure interaction is presented in terms of surface settlements, forces induced in the tunnel lining and forces along the piles. It should be noted that on the base of the obtained results, the MC model cannot accurately estimate the ground settlements and the forces in tunnel and piles, therefore it is necessary to use advanced constitutive models like CYsoil for design purposes.