Drained and undrained anisotropic elastic stiffness parameters

Equations that map drained to undrained elastic stiffness parameters in a cross-anisotropic material are presented. Graphs of various anisotropic stiffness ratios are used to illustrate the important trends. A new 2-D graph showing the elastic bound enables measured elastic parameters to be plotted, which all lie well within it. The 2-D graph enables uncoupled and incompressible materials to be shown, plus materials with particular initial effective stress path slopes in an undrained triaxial test. Bounds more restrictive than the elastic one are also discussed, and the likely ranges of various anisotropic stiffness ratios are presented. In general, undrained anisotropy is much less than drained: that is, closer to isotropic. In undrained plane strain conditions, vertical and horizontal moduli are found to be the same. In drained plane strain conditions, the ratios of the moduli are almost the same as the Young's moduli.