Drained expansion responses of a cylindrical cavity under biaxial in situ stresses: numerical investigation with implementation of anisotropic S-CLAY1 model

Cavity expansion theory has been well developed in the past few decades, but little progress has been made to cavity ex-pansion theory regarding biaxial in situ stresses. Owing to the two-dimensional nature of cavity expansion under anisotropic in situ stresses, a rigorous analytical or semi-analytical solution is no longer available for such cavity expansion problems. In this paper, a numerical study is performed to investigate the drained expansion responses of a cylindrical cavity under biaxial in situ stresses. The advanced anisotropic S-CLAY1 model integrated by the fully implicit backward Euler algorithm is implemented as a user-defined materials (UMAT) subroutine in the finite element model (FEM) to represent the elastoplastic be-haviors of the anisotropic soils during cavity expansion. The FEM is validated by comparing with a benchmark semi-analytical solution under the uniform in situ stress. The expansion responses under biaxial in situ stresses, including the distributions of stress components, the evolutions of expansion pressures, stress paths, and yield surfaces, are subsequently investigated on leverage of the FEM and compared with those from approximate solutions. The present FEM in conjunction with the UMAT subroutine provides a benchmark for the validation of approximate solutions and the outcomes give significant insights into practical geotechnical problems pertaining to cavity expansion under biaxial in situ stresses.