Abstract: In order to study undrained mechanical properties of anisotropically consolidated soft clay under initial deviation of principal stress axes, a series of undrained shear tests were conducted on the anisotropically consolidated soft clay using the GDS hollow cylinder apparatus to investigate the influence of different principal stress axes directions on deformation, strength, and non-coaxiality behavior.The test results indicate that the strain development, stress path and pore pressure development are all dependent on the principal stress orientation, and there are three patterns of deformation, namely vertical compression, shear deformation and radial extrusion, respectively.Compared with the isotropic consolidation case, the undrained shear strength of the anisotropically consolidated sample is enhanced, showing an approximate semi-elliptic strength envelope surface in the τ_zθ-(σ_z-σ_θ)/2 plane, which demonstrates significant strength anisotropy.The soil strength tends to decrease and then increase as the angle of the major principal stress axis α₀ increases from 0° to 90°, and it reaches the maximum and minimum value at α₀=0° and 45°, respectively.Furthermore, the non-coaxial angle decreases gradually during undrained shearing, the samples show a near zero non-coaxial angle when samples are subjected to pure compression, pure twist-shear and side extrusion.The non-coaxial phenomenon manifests obviously when the soil samples are in compressed twist-shear and extruded twist-shear.