Abstract
Rock stress is of great interest in cavern excavation, hot dry rock geothermal development and others. At great depth technically and economically usable methods for stress measurement are not many, and it is not rare that only methods based on laboratory core tests are available or stress induced rock failure phenomena like corediscing may give stress information. Stress induced failure phenomena like corediscing are straightforward information about stress state in a rock. On the other hand, core based methods have assumptions in their principles to some extent and hence they are not yet widely accepted. Whether the core based methods become to be truly reliable depends on the accumulation of the comparisons to other clear stress indicators.
This paper reports one of them. Corediscing was observed in a granite from 1,000 m depth at Akita pref., Japan. Test specimens for DSCA and AE methods were retrieved just adjacent to the discing point. Estimated rock stress state at the point were in agreement both in the maximum stress direction and the stress value with the corediscing criteria presented by Sugawara et al. and Matsuki et al. Also the spatial variation of stress state were observed in accordance with the structural condition of the rock. The average stress estimated by the core test was found to be in accordance also with shut-in pressure. Thus DSCA and AE methods were found to be basically reliable methods.
The specimens were tested about 6 years after the coring at the geothermal region and gave reasonable estimate of rock stress. Therefore it is also said that the effect of heat and the time from core retrieving to test can be not significant.
