Evaluation of Rock Inclusion Geometrical Complexity and its Influence on Fracturing Process by AE Measurement

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Underground rock masses and rock slopes consist of various rock types having different physical properties and geometry. In such rock engineering sites, unexpected failures tend to occur when rocks containing inclusions are affected by stress change. Depending upon geometry and physical properties of the inclusion in matrix rock, stress concentration induces local fractures with acoustic emission (AE) and catastrophic failure can occur. To monitor an unstable rock area using AE techniques, it is therefore important to know the relationship between inclusion rock features and AE activity.In this study, using cylindrical and plate-shaped rock specimens consisting of andesite and tuff, Brazilian and uniaxial compression tests were carried out to determine the relationship between AE source locations and complexity of inclusion geometry appearing on the surfaces of sliced specimen sections. Geometrical complexity was represented by some texture analysis indexes. Also, to evaluate local stress concentration areas, 2-D FEM analysis was conducted for the sliced specimen sections.Experimental and analytical results are :1. The number of AE events during loading was found to depend on the ratio of inclusion volume to the specimen. The AE waveform from the andesite area contained higher frequency components than the tuff area waveform.2. Most AE sources were located along the eventual fracture plane ; some of them were located along the inclusion-matrix boundary which was estimated to concentrate local stress by FEM.3. More AE sources were found to be present in sliced sections with a higher complexity index value of inclusion. It was believed that local stress concentration occurred in sections with a complex structure and that more microfracturing was therefore generated with AE.