Effects of Initial Direction and Subsequent Rotation of Principal Stresses on Liquefaction Potential of Loose Sand

摘要

The effects of the initial orientation of principal stress axes and subsequent rotation of principal stresses on liquefaction susceptibility of sands were investigated. Monotonic and cyclic hollow cylinder torsional shear tests were carried out on Fraser River sand specimens consolidated to different initial principal stress orientations and subjected to principal stress rotation during loading. Cyclic loading was applied with constant amplitude cyclic deviator stress, but along stress paths that impose different magnitudes of principal stress rotation. Test results demonstrate that the cyclic resistance ratio (CRR) is influenced by both the initial orientation of principal stresses and the magnitude of stress rotation during dynamic loading. These results suggest that the degree of stress rotation influences CRR more significantly than the initial principal stress orientation. Yet, the effects of the degree of stress rotation are not considered in current liquefaction assessment practice. The only available mechanism to account for principal stress directions is the use of the K_α factor, which focuses on the initial principal stress orientation only. Irrespective of the initial inclination of the major principal stress axis, the weakest cyclic resistance was noted in tests with a principal stress rotation of ±45°. The increased susceptibility to liquefaction is possibly due to factors such as the inclination of the plane of maximum shear stress with the bedding plane, inclination of major principal stress with the bedding plane, the presence of horizontal shear stress, and the nature of the variation of shear stress on the weak bedding plane.