The demand for the long-term safety utilization of rock structures has increased further in recent years. It has been reported that repeated stress changes induced the deterioration of rocks. However, there still remain many unknowns about the deterioration of rocks by repeated stress changes. To obtain further insights into the deterioration of granite by repeated stress changes, changes in elastic properties of specimens during the test were analyzed and microcrack growth patterns within specimens stressed to the different stages were observed.

Cylindrical Westerly granite specimens were subjected to the cyclic loading with 0.5–160MPa (80% of the estimated UCS). Axial and lateral strains, and the applied load were simultaneously measured at 100 points for one cycle, and Young's modulus and Poisson's ratio of each cycle until failure were estimated. A series of cross-sectional thin sections of the prefailure specimens were observed. As a result, the characteristic changes in two elastic properties following the progress of the deterioration stage were revealed. At the initial degradation stage, the changes were very small. During the second steady stage, two properties were changed gradually and linearly. At the final accelerated stage, the changes were drastically. It was found that these characteristic alterations were well accorded with the observed microcrack growth patterns.

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