Slate frequently encountered in numerous engineering applications basically exhibits significant anisotropies in terms of physico-mechanical properties due to the presence of well-developed foliation structures. The objective of this study is to investigate the mechanisms of foliation effects on the mechanical and failure characteristics of slate in three-dimensional (3D) space under Brazilian test conditions. A series of laboratory tests are conducted on slate with seven different foliation angles ( φ ), which are defined as the angle between the foliation plane and end surfaces of the specimen. On the basis of each foliation angle, five different loading angles ( θ ), which are defined as the projection of the angle between the loading surface and the foliation plane on the front side of the specimen, are selected to ensure that 3D space is involved. The high-speed camera and acoustic emission (AE) system are employed to analyse the failure characteristics of slate during loading process. The testing results indicated that the variations of applied failure force (AFF) with respect to loading angle ( θ ) significantly differ under varied foliation angles. With increase of foliation angle, the anisotropy ratio of the maximum to minimum AFF shows an increasing trend, suggesting that the anisotropy becomes more notable. The high-speed camera visually recorded the initiation and propagation of cracks. The specimen failure can involve two major processes: the local cracks first occurred on the disc flank, and then the fully connected cracks were formed causing the overall failure. The rupture evolution process inside the specimen was characterised by AE energy and AE hits, which was in good agreement with the high-speed camera observations. When the foliation angle is small, i.e. 0° ≤ φ ≤ 15°, or large, i.e. 75° ≤ φ ≤ 90°, the macro-cracks on both sides (i.e., front and back) show similarity to some certain, and the fracture patterns can be considered as two-dimensional (2D). However, when φ is in the range of 30°–60°, the fractured surfaces have 3D spatial distribution characteristics, and the macro-cracks appearing on both sides exhibit an approximately anti-symmetric relationship. It is also revealed that both φ and θ have significant effects on the AFF and the fracture patterns. The results are likely to provide experimental basis for further improving the theory of tensile properties of anisotropic rocks.

中文翻译：

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在巴西测试条件下，3D 空间中叶层对板岩力学和破坏特性的影响

由于存在发育良好的叶理结构，在众多工程应用中经常遇到的板岩在物理机械特性方面基本上表现出显着的各向异性。本研究的目的是在巴西测试条件下研究叶理效应对三维 (3D) 空间中板岩力学和破坏特性的影响机制。一系列实验室测试在具有七种不同叶理角 ( φ ) 的板岩上进行，这些叶理角被定义为叶理平面和试样端面之间的角度。在每个叶理角的基础上，定义五个不同的加载角（ θ ），它们定义为加载表面与试件正面叶理平面之间的角度的投影，选择以确保涉及 3D 空间。采用高速摄像机和声发射（AE）系统分析板岩在装载过程中的失效特征。测试结果表明，在不同的叶面角度下，施加的破坏力 (AFF) 相对于加载角度 ( θ ) 的变化显着不同。随着叶理角的增加，最大与最小 AFF 的各向异性比呈增加趋势，表明各向异性变得更加显着。高速摄像机直观地记录了裂纹的萌生和扩展。试件失效可涉及两个主要过程：首先发生在盘侧面的局部裂纹，然后形成全连接裂纹导致整体失效。试件内部的破裂演化过程以声发射能量和声发射撞击为特征，与高速相机观测结果吻合较好。当叶理角小，即0°≤φ≤15°，或大，即75°≤φ≤90°时，两侧（即正面和背面）的宏观裂缝表现出一定的相似性，并且断裂模式可被视为二维 (2D)。然而，当φ在30°～60°范围内时，断裂面具有三维空间分布特征，两侧出现的宏观裂纹呈现近似反对称关系。还表明 φ 和 θ 对 AFF 和断裂模式都有显着影响。研究结果可能为进一步完善各向异性岩石拉伸特性理论提供实验依据。