Anisotropy in the undrained pore pressure response of rock

In Biot’s theory of isotropic poroelasticity, deviatoric stress does not induce pore pressure as the mean stress is the solely factor responsible for such changes. However, for an anisotropic rock the deviatoric stress can induce an undrained pore pressure change, a consequence that does not happen under the assumption of isotropy. Experimental techniques have been aimed at making reliable measurements of Skempton’s coefficients taking into account the effect of the dead volume of the drainage system. Special attention has been dedicated to full saturation with the use of the back pressure technique. The hydrostatic compression experiment has been utilized to confirm the anisotropy of the bulk and solid phases of the rock. The conventional triaxial compression experiment has been performed on transversely isotropic rock where independent loading is applied perpendicular and parallel to bedding directions and the correspondent changes in pore pressure in the specimen are recorded. This has lead to interesting observations on the connections between the directional-dependent solid and bulk response of rock.