X‐ray computed tomography (CT) imaging and digital image correlation techniques are applied to study spatial cracking behaviors of sandstone under uniaxial compression, in which the angle between precracks is 45°, 90°, and 135° and the crack depth is 7.5 mm and 10 mm, respectively. Layered anisotropy damages and spatial cracking evolution are quantitatively analyzed by the defined digital layered anisotropy index and digital damage ratio, respectively. Three cases with different array of precracks evidence the depth effects of precracks on spatial crack propagation. Results show that the failure process of samples is first controlled by the coalescence of surface cracks in 2D space and then the samples are failed by the propagation of coalesced cracks (shear cracks with different shapes). The crack types for samples with precrack depth of 7.5 mm are all shear cracks for Cases 1‑3. Nevertheless, the crack types for samples with precrack depth of 10 mm are, respectively, the half X‐shape crack for Case 1, X‐shape crack for Case 2, and double shell crack for Case 3. The precrack has a significant promotion effect on the failure process when the angle between the two precracks is β = 90°, and the precrack has little to no effect on the failure process when the angle between the two precracks is β = 135°. As the depth of precrack increases to 10 mm, the crack types are changed in this study. The peak strength of sample subjected to uniaxial compression decreases with increasing depth of precracks, implying the decrease of the rock strength by the discontinuity.

中文翻译：

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单轴压缩下含预裂细砂岩的数字空间开裂行为

X射线计算机断层扫描（CT）成像和数字图像相关技术被用于研究砂岩在单轴压缩下的空间开裂行为，其中预裂纹之间的夹角为45°，90°和135°，裂纹深度为7.5 mm和10毫米。通过定义的数字分层各向异性指数和数字损伤率分别定量分析了分层各向异性破坏和空间裂缝演化。3个预裂纹阵列不同的案例证明了预裂纹对空间裂纹扩展的深度影响。结果表明，样品的破坏过程首先受二维空间中表面裂纹的合并控制，然后由于聚结的裂纹（形状不同的剪切裂纹）的传播而使样品破坏。预裂纹深度为7的样品的裂纹类型。情况1-3的所有剪切裂纹均为5毫米。尽管如此，预裂纹深度为10 mm的样品的裂纹类型分别为案例1的半X形裂纹，案例2的X形裂纹和案例3的双壳裂纹。预裂纹具有显着的促进作用两个预裂纹之间的夹角为β = 90°，并且当两个预裂纹之间的角度为β = 135°时，预裂纹对破坏过程几乎没有影响。随着预裂深度增加到10 mm，本研究中的裂纹类型也随之改变。样品的峰值强度随预裂深度的增加而降低，这意味着岩石强度由于不连续性而降低。