Progressive damage of granite under constant loading

The study of failure of a rock under constant loading is essential to the design and construction of excavations in the rock for mines, tunnels, and nuclear waste repositories. The constant loading test on granite with acoustic emission monitoring clearly shows the progressive damage process. The inelastic volumetric strain is proportional to cumulative acoustic emission counts, which indicate that the damage within granite is attributed to micro-cracking or micro-fracturing within granite. Three creep phases can be determined more easily from the cumulative acoustic emission count. Source location analysis also shows the progressive damage process under constant loading. During primary creep, cracks distribute randomly and then cluster into several nucleation zones. During secondary creep, some clusters become more active while others decay off. During tertiary creep, the activities of the active cluster become stronger until the sample fails.