Nonlinear anisotropic finite element analysis of liquefiable tunnel–sand–pile interaction under seismic excitation

Nonlinear time-history analysis can be used to determine the liquefiable behaviors of the tunnel–sand–pile interaction (TSPI) model with the consideration of sand anisotropy. This study presents the nonlinear response of the TSPI model with the existence of liquefaction under seismic excitation. The analysis reveals that tunnel and pile behave as isotropic elements, while sand shows isotropic, orthotropic, and anisotropic characteristics. Three constitutive models including UBC3D-PLM (two yield surfaces associated with the hardening rule), NGI-ADP (yielding with associated plastic potential function), and a user-specified constitutive model are adopted to evaluate the isotropic, orthotropic, and anisotropic behaviors of sand. On this basis, two finite element-based codes (ETABS 18.1.1 and Plaxis 3D) are used to evaluate sand behaviors and responses. Responses of the tunnel, sand, pile, and excess pore pressure ratio are recorded in the interaction zone by varying the pile diameter, tunnel diameter, and tunnel–pile clearance. Compared with the orthotropic and isotropic conditions, lower variations of results are found in the anisotropic condition, except for the case of generation of excess pore pressure. In addition, the present reanalysis results are in agreement with previous analytical and case study results, which further indicates the effectiveness of the finite element-based numerical codes.