The 31th U.S. Symposium on Rock Mechanics (USRMS),
1990. A. A. Balkema, Rotterdam. Permission to Distribute - American Rock Mechanics Association
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INTRODUCTION Acoustic emission (AE) has been described in ASTM E610-77 as the class of phenomena whereby transient elastic waves are generated by the rapid release of energy by a localized source or sources within a material, or the transient elastic wave so generated. The transient elastic waves will take a form of displacement vibration in the material which can be detected by diplacement gauges or accelerator gauges. These gauges are called AE transducers. AE is related to the internal changes of material structure which are caused by external physica 1 actions, such as load and temperature. For rock materials, AEreveals the internal fracturing and deforming processes within. This property has been widely used to monitor the stability of engineering structures in the field (Hardy, 1981; Koerner, et al., 1981). AE will start when the load on rock exceeds some level, and the intensity of AE will increase with increasing loads. Mogi (1962) gave an AE signature pattern, which has corresponding relations with the physical model of fracturing processes by Bieniawski (1967).
The Kaiser effect is an AE phenomenon briefly defined as the absence of detectable acoustic emissions until the previously applied stress level is exceeded. This effect is based on the experimental discovery by Kaiser (1950), that metal materials had the capability to remember the previous maximum stress level. This capability was also discovered in rock materials (Kurita and Fujii, 1979). Some efforts have been made to use the Kaiser effect to estimate geostresses (McElroy et al. 1985; and Hughson and crawford, 1987). A number of papers have been published where AE has been used in fracture toughness tests (for instance Suzuki et al. 1978). Barron (1971) conducted a preliminary study of AE as a detector of fracture initiation.
In the present investigation, the fracturing processes within rocks subjected to a uniaxial compresslye load have been evaluated by the AE features during the whole loading period. Also, the Kaiser effect in rock materials has been studied.
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