抄録
In order to obtain higher quality AE (acoustic emission) signals during triaxial compression experiment, we designed a new co-axial type outlet which is insulated from the pressure vessel. The ratio of signal to noise was improved by about 15 db using this outlet.
A cylindrical sample of Yugawara andesite was triaxially compressed under a confining pressure of 20MPa. AE waveforms and strains were simultaneously detected by 20PZT transducers and 6 strain gauges attached to the sample surface. The sample fractured in a brittle manner at a differential stress of about 390MPa with fracture planes nearly parallel to the loading axis. Hypocenters were determined for 163 AE events that occurred at the differential stress more than about 60% of the fracture strength. The hypocenters were randomly distributed below about 94% of the fracture strength. Just above this stress, AE events began to swarm around one of the fracture planes. Near the swarm region, anomalous decrease of local volumetric strains preceded to the onset of the swarm activity. Temporal variation of the anomalous strain behavior seems to be fairly consistent with the swarm activity.
