[SCG69-P04] Dependency of crack distributions in granite on elastic velocities
Keywords:elastic wave velocity, granite, laboratory experiment, cracked rock
In this study, we generate cracks in granite specimens by heating them up to 550℃ or 650℃ then rapidly cooling with ice water, and we clarified the relationship among the crack distribution, porosity and elastic wave transmission properties. Cylindrical specimens (25 mm in the diameter and 30 mm in the length) of granite from Oshima, Ehime Prefecture (initial porosity: 0.46±0.02 %, P and S wave velocity (VP, VS) under water saturated condition: 6.12±0.06, 3.17±0.10 km/s, respectively), and granite from Inada, Ibaraki (initial porosity: 0.68±0.02 %, VP, VS under water saturated condition: 6.06±0.04, 3.07±0.09 km/s, respectively) were used for the experiments. Average mineral size of Inada granite is larger than Ohshima granite. We operated experiments to transmit P and S wave through the granite specimens which is dry or saturated with water, under atmospheric pressure.
Porosity is increased as a heating temperature is increased. Porosity of Inada granite is approximately 1.3 to 1.5 times larger than that of Ohshima granite for intact and heated rocks. There is no clear difference on the relationship between porosity and VP, VS between Inada and Ohshima granite. VP and VS are negatively correlated with porosity: in the case of water saturated specimens, as porosity is increased from 0.4% to 4.3%, VP and VS is decreased approximately 32% and 55%, respectively. We are planning to evaluate crack distributions in the specimens, and investigate the relationship between the crack distribution and the measurement results.