Heteroscedasticity of axial strength of transversely anisotropic rock

Some previously published triaxial strength data of Delabole slate and Angers schist are re-analysed. The strength data are grouped according to the orientation of the anisotropy plane relative to the applied major principal stress, and Bayesian regression is used to model peak strength as a linear function of confining pressure for each group. The analysis indicates that not only the magnitude but also the variance of strength and the effect of confining pressure on strength are orientation dependent. These dependencies have profound ramifications for the implementation of a geotechnical limit state design framework.