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

地下岩体和岩坡由具有不同物理性质和几何形状的各种岩石类型组成。在此类岩石工程场地中，当含包裹体的岩石受到应力变化的影响时，往往会发生意外破坏。根据基体岩石中包裹体的几何和物理性质，应力集中会引起局部裂缝，并伴有声发射（AE），从而发生灾难性破坏。因此，为了利用声发射技术监测不稳定岩石区域，了解包裹体岩石特征与声发射活动之间的关系非常重要。本研究利用安山岩和凝灰岩组成的圆柱形和板形岩石试样进行巴西压缩试验和单轴压缩试验，确定声发射源位置与切片试样断面表面包裹体几何形状复杂性之间的关系。几何复杂度由一些纹理分析指标来表示。此外，为了评估局部应力集中区，对试样切片进行了二维有限元分析。实验和分析结果如下：发现加载过程中声发射事件的数量取决于夹杂物体积与试样的比例。安山区声发射波形的频率分量高于凝灰岩区声发射波形。大多数声发射源位于最终断裂面上；其中一些沿包裹体-基体边界分布，通过有限元分析估计其局部应力集中。切片中发现声发射源较多，包含物的复杂性指数值也较高。认为结构复杂的剖面存在局部应力集中，因此声发射产生的微裂缝较多。

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.