Abstract Bimrocks are a kind of rocks in which blocks are randomly distributed in a matrix. Despite their wide distribution in nature, their significant effects on the failure of rock structures such as slopes, mines and tunnels have been neglected. Bimrocks behave differently than any other rock types as they contain mix of blocks (of different strength, size and distribution volume in matrix) and a matrix (of different physical and mechanical characteristics). The interaction between the blocks and matrix are complex making the study of deformation and cracking of such rocks difficult under loading. Therefore it is of great importance to fully understand their behaviour in a micro level. Dynamic loading adds more complexity to this kind of complex rocks and demand comprehensive assessment. This study investigates the crack initiation and failure of bimrocks under experimental dynamic impact loading analyses via digital image correlation (DIC) method. Split Hopkinson pressure bar (SHPB) is combined with a high speed camera to record videos of entire loading for the image analysis purposes. Three sets of bimrocks with various block dimensions (small, medium and large) are prepared and loaded to assess the effects of blocks dimensions on the deformation behaviour. Also the specimens are dynamically loaded under one low (150 1/s) and one high (300 1/s) impacts to better evaluate the failure of such rocks. The DIC results show that the bimrocks with large blocks exhibit considerable tortuosity in the crack path and an extensive irregular failure develops. The bimrocks having medium sized blocks show high degree of crack tortuosity and irregular failure is also seen, but much less than the large blocks. The small blocks have almost no influence on the failure pattern and the bimrocks with small blocks behave similar to an intact rock. Moreover, large blocks exhibit significant shear crack initiation in the block-matrix contacts inclined with regard to the loading direction and then tensile cracks initiate from the shear cracks. This behaviour is also observed in medium blocks. Small blocks only exhibit tensile cracking. Interestingly, large blocks carry the lowest load, while the small blocks show the highest dynamic peak load due to the less presences of weak contacts. Under high impact pressure some blocks are broken while under low pressure no block breakage is observed. The comparison between the quasi-static and dynamic tests reveals that the loading rate has small effect on the failure pattern, while the block sizes play a significant role.

中文翻译：

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动态载荷下基于数字图像相关的bimrock裂纹萌生和破坏发展

摘要 Bimrocks 是一种块体随机分布在矩阵中的岩石。尽管它们在自然界中分布广泛，但它们对边坡、矿山和隧道等岩石结构破坏的显着影响却被忽视了。Bimrocks 的行为与任何其他岩石类型不同，因为它们包含块（在基质中具有不同强度、大小和分布体积）和基质（具有不同物理和机械特性）的混合物。块体和基质之间的相互作用很复杂，使得研究此类岩石在加载下的变形和开裂变得困难。因此，从微观层面全面了解他们的行为非常重要。动态加载增加了这种复杂岩石的复杂性，需要综合评估。本研究通过数字图像相关 (DIC) 方法研究了在实验动态冲击载荷分析下 bimrock 的裂纹萌生和破坏。分离式霍普金森压力棒 (SHPB) 与高速摄像机相结合，可记录整个加载过程的视频，用于图像分析。准备并加载三组具有各种块尺寸（小、中和大）的砖石，以评估块尺寸对变形行为的影响。此外，试样在一次低 (150 1/s) 和一次高 (300 1/s) 冲击下动态加载，以更好地评估此类岩石的破坏。DIC 结果表明，具有大块体的bimrock 在裂纹路径中表现出相当大的曲折性，并且会发展出广泛的不规则破坏。具有中等块体的bimrock 显示出高度的裂缝迂曲和不规则破坏，但比大块体少得多。小块对破坏模式几乎没有影响，带有小块的bimrock表现得类似于完整的岩石。此外，大块体在相对于加载方向倾斜的块体-基体接触中表现出显着的剪切裂纹萌生，然后从剪切裂纹开始拉伸裂纹。在中等块中也观察到这种行为。小块仅表现出拉伸开裂。有趣的是，大块承载的负载最低，而小块由于弱接触的存在较少而显示出最高的动态峰值负载。在高冲击压力下，一些砌块被破坏，而在低压下，没有观察到砌块破裂。