A Fully Coupled Flow Deformation Model for Seismic Response Analysis of Underground Structures in Liquefiable Sites

With an algorithm for equivalent shear strain and a loading–unloading criterion, the Davidenkov constitutive model is formulated in three-dimensional stress space. A method for effective stress analysis to capture soil–structure interaction in liquefiable sites is proposed, integrating the shear–volume-strain increment model and Biot’s dynamic consolidation equations. Implemented on the FLAC3D platform, it enables nonlinear seismic analysis of large-scale soil–structure systems. Various models simulate undrained cyclic torsional shear tests of saturated sand, revealing the proposed method’s superior capability in simulating liquefaction under complex stress paths compared to the modified Byrne model. Seismic response analysis of a rectangular tunnel in a liquefiable site is conducted to explore the soil–structure interaction mechanism. The results show that vertical seismic wave propagation induces reciprocating shear stress in the far field, with reflection and projection at the soil–structure interface amplifying excess pore pressure growth and liquefied zone area. While the modified Byrne model predicts seismic response well in the far field, it underestimates the excess pore pressure accumulation and the liquefied area around the structure. In contrast, the proposed method accurately captures the soil–structure interaction effects on the dynamic response in the liquefiable site surrounding the underground structure.