Influence of stress principal axis variation on anisotropic behavior of silty soil in the Yellow River flood area

A series of hollow cylinder torsion shear tests were conducted for the silty soil in the Yellow River flood area, considering the effect of drainage shearing with major large principal stress direction. The shear stress-strain behavior as well as the anisotropic characteristics of silty soil were investigated. Under different intermediate principal stress coefficients b and major principal stress direction angles α, the stress-strain relationship and the corresponding shear stress ratio of silty soil were obtained. It was concluded that the values of α and b have a significant effect on the octahedral stress-strain and the shear stress-major principal strain. The obvious anisotropicic behavior was observed, especially under b=0.5 or 1.0. Compressed deformation generally occurred in the major principal strain direction. Under a fixed α, the smaller shear strength occurred under a larger b value. The peak shear strength and the corresponding axial strain were the greatest under the conditions of α=45° and b=0.5, relevant with to the highest peak shear stress ratio q_f/p₀.