ABSTRACT:

Acoustic Emission (AE) is one of the nondestructive techniques, which is known as elastic waves generated due to crack initiation, crack formation and crack coalescence. Because AE is known as effective and sensitive for evaluating rock stability, a variety of research papers on AE application to rock monitoring have been reported (Goodman and Blake, 1966; Hardy, 1981; Nakajima et al., 1988). Although great deal of works were carried out in respect to AE monitoring in rock, successful results to evaluate and predict slope failure are quite few. This is partially because AE sensors are usually set in the vicinity of rock surface. To expand monitoring area, AE sensors of such lower resonant frequency characteristics as less than 10 kHz are employed. These surface setup and lower frequency characteristics of AE sensors easily bring remarkable amount of undesirable AE events due to natural phenomena. Since the frequency characteristics of AE waves ranges around 10 kHz (Shiotani et al., 1999c), it is difficult to eliminate such noises from AE data acquired. Moreover, in the case of monitoring rock failure, it is further difficult to completely take into account the state of the pre-existing joint properties, although several surveys on rock characteristics and joint conditions are performed prior to AE monitoring. Because AE waves generated within rock are normally reflected at the joints when they propagate, the existence of the joints would be a great problem to detect AE waves efficiently. Thus, it is necessary for AE monitoring in rock to develop an effective method for detecting AE waves which are not dominantly influenced by such conditions as natural noises and existing joints. In the paper, an installation method of AE sensors for AE monitoring in rock called WEAD is developed.

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