Change in Elastic Property of Granite by Repeated Stress Change

The demand for the long-term safety utilization of rock structures has increased further in recent years. It has been reported that the repeated stress change induced the deterioration of rocks. However, there still remain many unknowns about the deterioration of rocks by repeated stress change. To obtain further insights into the deterioration of granite by repeated stress change, change in elastic property of specimen during the test was analyzed in detail. Cylindrical Westerly granite specimen with 20mm in height and 10mm in diameter was subjected to the cyclic loading with maximum 160 MPa (approximately 80% of the estimated uniaxial compressive strength) and minimum 0.5 MPa at room temperature. 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 until failure were estimated applying these measured data. 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 also found that these characteristic alterations were well accorded with the reported microcrack growth patterns.