Abstract
The behavior of the loosened zone around rock caverns plays an important role in the mechanical stability of rock pillars during construction and after completion. The authors have carried out the laboratory and in situ experiments to investigate the failure mechanism of the rock around the caverns and the monitoring technique of the occurrence and progress of loosened zones by acoustic emission (AE) measurements.This paper describes the results of these experiments and discusses the available procedures to predict the initiation of the loosening of the rock mass by the indicators “count rate (the rate of occurrence of AE per minute or hour)”, “AE energy (the square of amplitude of AE)” and “m-value” (the ratio of amplitude to count rate of AE).(1) As the results of comparison between AE measurements by laboratory triaxial test and in situ rock shear test, the loosening of the rock mass is considered to be strongly affected by the presence of preexisting fractures.(2) As the results of AE measurements by in situ rock shear test and during tunnel excavation, it is clarified that the decrease ratio of m-value and the increase ratios of count rate and AE energy for the heavily jointed rock mass show smaller figures than those of the intact rock mass.(3) The decrease ratio of m-value and the increase ratios of count rate and AE energy could be appropriate indicators for the determination of the criteria for the judgement of occurrence of loosening based on the relationship between three AE parameters mentioned above and the seismic wave velocity.
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