Anelastic strain recovery method is one of inexpensive and simpler methods for measuring in-situ stresses at great depth. However, the method has been based on the critical assumptions that the vertical boring axis is one of principal directions and that vertical stress is given by overburden pressure, which are not always true for actual rock masses.
In this study, by deriving a fundamental equation on the anelastic strain recovery of isotropic visco-elastic material in general three dimensional stress state, the method for measuring three-dimensional in-situ stresses has been proposed. In the method, by measuring six independent anelastic normal strains of a core, six anelastic strain deviations and anelastic volumetric strain are determined first. From the former, the orientations of principal in-situ stresses and ratios of principal in-situ stress deviations are determined without the knowledge of anelastic strain recovery compliances of the core, in-situ pore pressure and temperature change in the core. Then, by evaluating pore pressure and by correcting the effect of temperature change on the anelastic volumetric strain, absolute three dimensional in-situ stresses are determined by measuring the anelastic strain recovery compliances of the rock core in both shear and volumetric modes in the laboratory.
