Abstract Discontinuities widely exist in natural rocks. To investigate the progressive micro-cracking process and failure mechanism of fissured rocks, a series of biaxial compression tests were conducted on sandstone specimens containing two parallel filled flaws using acoustic emission (AE) analysis synchronized with digital image correlation (DIC) monitoring. Experimental results show that the peak strength and elastic modulus of sandstone decrease first and then increase with the change in the ligament angle from 0° to 150°, achieving a minimum at 60°. The flaws remarkably facilitate crack coalescence under low lateral stress, such as at 2.5 MPa and 5 MPa. However, with an increase in lateral stress to 10 MPa, the crack coalescence is less influenced by the presence of pre-existing flaws. The AE events produced by flawed sandstone during the loading process conform to the Hurst statistical law. Fractal analysis shows that the lateral confinement reduces the irregularity of ultimate fracture geometry. Based on the AE dominant frequency features, the micro-tensile cracks, micro-shear cracks and micro-tensile-shear cracks are distinguished. The results show that with an increase in lateral stress, the percentage of micro-tensile cracks are constrained, but the number of micro-shear and mixed tensile-shear cracks increases. In addition, the micro-shear cracks preferentially appear in flawed sandstone specimens under high lateral stress as compared with specimens subjected to low stress.

中文翻译：

---

双轴压缩下两条平行填隙砂岩的开裂过程及声发射特性

摘要 天然岩石中广泛存在不连续性。为了研究裂隙岩石的渐进微裂纹过程和破坏机制，使用声发射 (AE) 分析与数字图像相关 (DIC) 监测同步，对包含两个平行填充缺陷的砂岩试样进行了一系列双轴压缩试验。实验结果表明，砂岩的峰值强度和弹性模量随着韧带角度从0°到150°的变化先减小后增大，在60°时达到最小值。这些缺陷在低侧向应力（例如 2.5 MPa 和 5 MPa）下显着促进了裂纹的合并。然而，随着横向应力增加到 10 MPa，裂纹合并受预先存在的缺陷的影响较小。缺陷砂岩在加载过程中产生的AE事件符合Hurst统计规律。分形分析表明，横向约束减少了最终裂缝几何形状的不规则性。根据声发射主频特征，可区分微拉伸裂纹、微剪切裂纹和微拉伸剪切裂纹。结果表明，随着侧向应力的增加，微拉伸裂纹的比例受到限制，但微剪切和拉剪混合裂纹的数量增加。此外，与承受低应力的试样相比，在高侧向应力下的有缺陷砂岩试样中优先出现微剪切裂纹。分形分析表明，横向约束减少了最终裂缝几何形状的不规则性。根据声发射主频特征，可区分微拉伸裂纹、微剪切裂纹和微拉伸剪切裂纹。结果表明，随着侧向应力的增加，微拉伸裂纹的比例受到限制，但微剪切和混合拉剪裂纹的数量增加。此外，与承受低应力的试样相比，在高侧应力下的有缺陷砂岩试样中优先出现微剪切裂纹。分形分析表明，横向约束减少了最终裂缝几何形状的不规则性。根据声发射主频特征，可区分微拉伸裂纹、微剪切裂纹和微拉伸剪切裂纹。结果表明，随着侧向应力的增加，微拉伸裂纹的比例受到限制，但微剪切和拉剪混合裂纹的数量增加。此外，与承受低应力的试样相比，在高侧向应力下的有缺陷砂岩试样中优先出现微剪切裂纹。但微剪切和混合拉伸剪切裂纹的数量增加。此外，与承受低应力的试样相比，在高侧向应力下的有缺陷砂岩试样中优先出现微剪切裂纹。但微剪切和混合拉伸剪切裂纹的数量增加。此外，与承受低应力的试样相比，在高侧向应力下的有缺陷砂岩试样中优先出现微剪切裂纹。