Development af AE detection system in rock masses

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The prediction of failure in rock masses in most important to design the excavation of rocks and to control the stability of underground openings. For the fundamental experiment of this purpose, time series fo acousitc emission (AE) events during uniaxial creep in Oshima granite were investigated. Both the origin time and the magnitude of AE events were measured simultanenously; by using the mictocomputer wuqipped system.First, the occurrence of AE events was analized graphically. Apparently, ther were no afrershock sequence which are observed with earthquakes. Second, whether the occurrence of AE events is a poisson process of not was examined at time intervals berween consecutive events. It was also tested by means of the x^2-test. The test shows that during the secondary creep the occurrence of AE events is a poission process unrelated to their magnitude. During the stage of tertiary creep, while the occurrenece of large AE events was a Poisson process except when the catastrophe was imminent, the occurrentce of smaller AE events began to deveate from the poisson process. To predict forthcoming instability, the analysis on the time-interval distribution of large AE events by plotting them on a Weibull probability scale was tried. The AE occurrence changed from being random to being periodic just prior to the main fracture.By using the obtained knowldge, the useful AE detection system in rock masses would be constructed in the near future.