Two of the most popular techniques used in the determination of in situ rock stresses are the stress-relief and high-modulus inclusion methods. Deformations and strains observed in the measuring instruments are usually interpreted on the assumption that the rock behaves as a homogeneous, isotropic, linearly elastic medium, a situation which is not even approximately correct in some practical cases.

This paper presents a theoretical analysis of the influence of: (a) rock anisotropy, of the transversely isotropic kind, on the accuracy of values of in situ stresses determined from the usual isotropic analysis and (b) time-dependent rock deformation, represented as linear, isotropic, viscoelastic creep, on the stresses developed in high-modulus plugs. It is shown that significant errors (over 50 per cent for one stress-relief example chosen) may be introduced by neglecting these factors.