Abstract: The constitutive model, which is closely related to deformation noncoaxiality induced by stress rotation, is used to investigate the influence of noncoaxiality on tunnel engineering simulation results. First, a noncoaxial model is formulated by incorporating the noncoaxial flow rule into the DruckerPrager considering the hyperbolic hardening rule. Subsequently, necessary deduction of the iteration process of the semiimplicit algorithm for the model is completed. Based on previous theoretical results, the semiimplicit algorithm is programmed into ABAQUS/Standard using the user subroutine UMAT. Finally, a typical finite element model for the tunneling in the plane strain is applied to the numerical analysis. The calculated results show the following: (1) Two intersecting plastic bands are developed from the waist of the tunnel. The longer band originates from the model with a smaller noncoaxial modulus. (2) The smaller noncoaxial modulus results in a larger zone with stress rotation and a larger extent of the rotation of the principal stress. (3) A model with a smaller noncoaxial modulus produces a larger surface settlement induced by the tunneling. (4) The extent of convergence of the tunnel at the bottom and along the sides increases with decreasing noncoaxial modulus.

Key words: noncoaxiality, soil deformation； semiimplicit integration algorithm, tunnel excavation; surface settlement