Our previous experimental studies showed that the initial stress in rocks estimated from the Kaiser effect of acoustic emission is not necessarily the maximum stress that the specimen is subjected to, but is correlative to the residual strain in the specimen at the time of testing. The present investigation on the characteristics of the Kaiser effect in various rocks revealed that the initial stress estimated from the Kaiser effect tended to decrease with time after coring. Thus, the experiments to estimate the initial stress existing in a rock mass by means of the Kaiser effect, must be conducted as soon as possible after coring rock samples.
When constructing large underground caverns such as hydraulic power stations and oil storages, it is important to estimate the loosened area around rock caverns caused by excavation. If the loosened area around a rock cavern is known, the most suitable support members and quantities can be determined. The authors have carried out in situ experiment to investigate the crack growth into rock mass by acoustic emission (AE) measurement.In this paper, parameter analysis, locational analysis and moment tensor analysis based on the observed AE signal waves were carried out to make clear the diffusing patterns, locations, orientations and crack types of AE sources. The following conclusions were obtained: (1) Many large amplitude AE signal waves diffused within about ten minutes after cavern blasting, (2) The concentrated areas of tensile cracks and shear cracks around a rock cavern were different, (3) From the distribution of observed AE signal waves, the loosened area was estimated within depth of 2m from the excavated wall.
when constructing large caverns such as the one used for an underground powerhouse, it is of extreme importance to assure the stability of the cavern. As one of the techniques for stability monitoring, uniaxial compression tests were performed in various rocks and acoustic emission(AE) activity was measured. From the examinations of AE activity and the maximum amplitude of a single event, two types of AE occurrence patterns and three types of m-value variations were found. When predicting failure modes by means of AE, it is thought that the total AE counts and the m-value can be useful for non-homogeneous rocks. On rocks of schistose or very homogeneous structures, the total AE counts provide useful information on failure prediction but the m-value does not. Furthermore, from the results of spectral analysis of AE signal waves measured, it is found that the dominant frequency increases with increasing load.
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