SIGNIFICANCE OF AE-BASED b-VALUE IN THE STUDY OF PROGRESSIVE FAILURE OF BRITTLE ROCK: SOME EXAMPLES FROM RECENT EXPERIMENTS
M. V. M. S. RAO
National Geophysical Research Institute, Hyderabad 500 007, India
Keywords: NDT, Acoustic Emission, rock, failure Assessment, mine
ABSTRACT Presented in this paper are the results of a laboratory investigation for evaluating and establishing the significance of amplitude distribution and b-value (slope of the log-linear frequency-magnitude relation) of acoustic emissions (AE) preceding the failure of brittle rock. The experimental tests were made at constant loading rate under unconfined compression using a granite, sandstone and some burst-prone rocks of Kolar gold mines, India**. The digital strain data and AE statistics, along with the AE wave forms recorded on videotapes were processed and analysed at the end of each test using a Dunegan- Endevco Distribution Analyzer**. Instantaneous AE based b-value could also be estimated by examining and processing subsets of AE wave forms in sequential non-overlapping time windows. Such a kind of approach has revealed that the amplitude distribution function of AE itself shows great promise for tracking and characterising the various stages of crack (population) growth in dilatant rock. Consequent to the preponderance of relatively high amplitude AE events at stresses close to failure, the b- value not only decreases sharply to reach a minimum (0.4 - 1.2), but also shows short-term anomalies in terms of the underlying physical processes of crack growth in rocks containing weak planes as observed in the present study. ** Experimental tests and data processing were carried out by the author at the Rock Mechanics Research Laboratories, Pennsylvania State University, USA.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 4, pages 2463 - 2468
Publisher: Ashgate Publishing Company
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