Strength properties of transversely isotropic soils based on characteristic mobilized plane

Based on the internal friction of materials, the concept of the mobilized plane aims at revealing the mechanism of soil failure from the perspective of geometrical and physical mechanisms. With the characteristic stress concept, the characteristic mobilized plane under two-dimensional stress conditions is put forward, and the failure stress conditions of materials on the characteristic mobilized plane and those corresponding to the stress Mohr circle are derived. In addition, based on the existing understandings on the strength characteristics of the transverse isotropic soils, and also the relative positions among the major principal stress, the normal of the bedding plane and the normal of the characteristic mobilized plane, the characteristic strength parameter, as well as the failure stress conditions, are proposed by projecting the microstructure tensor into the relative orientation tensor between the characteristic mobilized plane and the bedding plane. The orientation effect of the bedding plane is also analyzed on the basis of the proposed failure condition. The correspondences of the relative orientation angle ζ between the bedding plane and the characteristic mobilized plane and the direction angle δ between the bedding plane and the major principal stress, as well as the effects of ζ and δ, are also analyzed. By using the sample preparation mould developed for the true triaxial tests with the freezing method, the samples with different bedding plane angles are prepared and used to carry out triaxial compression tests. The understanding and proposed failure condition for the failure of the transverse isotropic soils are verified by the predicted test results in this paper and in the literatures.