Abstract
A scale model study was carried out to clarify the source mechanisms of acoustic emissions induced.by excavating an underground flat opening. AE signals during excavation were detected by six accelerometers embeded in the strata model and their source mechanisms were determined from two dimensional moment tensor inversion.The experimental results confirmed that the source mechanisms of acoustic emissions depended on their source location relative to the opening. The AE waveforms from the front of the opening showed compression or double-couple type of source mechanism. The more the source location was remote from the opening, the more double-couple type became predominant. On the other hand, the AE signals above the opening showed broad spectra in their source mechanisms including tensile type as well.A numerical experiment by FEM suggests that moment tensor of AE around an underground opening reflects stress tensor by which the fracture criterion of the focal region of AE is satisfied.
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