Strength Criterion Associated with the Loading Direction for Transversely Isotropic Soils

The strength properties of transversely isotropic soils are closely related to the loading direction. These direction-dependent properties have been testified by a series of laboratory tests. Two primary features for peak strength are obtained: the distortion of the strength curve on the deviatoric plane and the change of the internal friction angle associated with the direction angle between the major principal stress-acting plane and the depositional plane. How to describe these two features in a unified way is a difficult and hot research topic. This paper aims at solving this problem by proposing a strength parameter that was obtained by projecting the microstructure tensor on the direction of the spatial mobilized plane. It is an approach to extend an isotropic strength criterion into a transverse isotropy one. The combination of the proposed strength parameter with the isotropic non-linear unified strength criterion can well capture the distorted strength curve and its evolution with the increase of direction angle. The effects of the intermediated principle stress ratio b and the direction angle δ are also analysed. Material parameters in the proposed criterion can be conveniently obtained from the conventional laboratory tests. It is demonstrated that the new proposed criterion can be verified favorably by the test results.