Anelastic strain recovery compliance of rocks and its application to in situ stress measurement

Laboratory experiments were performed under uniaxial compression for seven rocks, to measure anelastic strain recovery (ASR) compliance in volumetric and shear modes. Together with previous experiments in uniaxial, hydrostatic and triaxial compression, the effects of both the rock type and the magnitude of stress on ASR compliance in both modes were analyzed, with particular focus on long-term ASR compliances resulting in ultimate values of JaV2f and JaS2f in volumetric and shear modes, respectively. The results showed that the values of JaV2f and JaS2f obtained in uniaxial compression at 50% of the uniaxial compressive strength can be approximately determined by the tangential Young's modulus at 50% of the uniaxial compressive strength (E50). The ratio JaV2f/JaS2f obtained in uniaxial compression at 50% of the uniaxial compressive strength converges within a narrow range at a sufficient elapsed time for all of the rocks used in this study, whereas the long-term ASR compliances in both modes are not a similar function of time. The ratio JaV2f/JaS2f significantly decreases with the mean normal stress since JaV2f decreases and JaS2f increases as the mean normal stress increases. Thus, a method is suggested for determining the approximate magnitudes of principal stresses without referring to ASR compliance but rather by considering the effect of the mean normal stress on long-term ASR compliance. This method was verified by applying it to experimental data. Furthermore, a method is proposed for determining the applicability of the ASR method prior to its application in the field by using the depth and the value of E50.