Multi-crack propagation is investigated mainly by experimental measurement and little by theoretical prediction. The classical fracture criteria can better predict tensile fracture under arbitrary loading conditions (pure tensile, pure shear and mixed-mode), but have difficulty in predicting shear fracture. In this paper, Mode I and Mode II SIFs of branch-cracks initiated by the original cracks were calculated by the complex function and superposition method, and a new theory of multi-crack propagation was established based on the criterion of maximum tensile-shear SIF ratio. Theoretical results of two collinear cracks under uniaxial compression show that the cracks initiate more easily at α = 30∘ (the crack inclination angle) than other angles. Coalescence of branch-crack only occurs at α = 45∘ with the maximum crack propagation length. Peak stress (Pun) reaches minimum when α ≈ φ (inner friction angle of rock), and the larger the α, the closer to the compressive strength of rock the Pun. Mechanism of the crack initiation and propagation are all Mode I under uniaxial compression. Uniaxial compressive test results of red sandstone (the rock material is assumed to be homogeneous) pre-cracked specimens agree well with predicted results of the crack initiation, stable and unstable propagation, which can prove the validity of the new multi-crack propagation prediction method.

中文翻译：

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一种预测脆性岩石双裂纹扩展轨迹的新方法

多裂纹扩展主要通过实验测量来研究，很少通过理论预测来研究。经典断裂准则可以更好地预测任意加载条件下的拉伸断裂（纯拉伸、纯剪切和混合模式），但难以预测剪切断裂。本文采用复函数叠加法计算了原始裂纹引发的分支裂纹的I型和II型SIF，并建立了基于最大拉剪SIF准则的多裂纹扩展理论。比率。单轴压缩下两条共线裂纹的理论结果表明，裂纹在α = 30∘（裂纹倾角）大于其他角度。分支裂缝的聚结只发生在α = 45∘具有最大裂纹扩展长度。峰值压力(磷联合国)达到最小值时α ≈ φ（岩石的内摩擦角），越大α, 越接近岩石的抗压强度磷联合国. 裂纹萌生和扩展的机理都是单轴压缩下的I型。红砂岩（假设岩石材料均质）预裂试件单轴抗压试验结果与裂纹萌生、稳定和不稳定扩展预测结果吻合较好，可以证明新的多裂纹扩展预测方法的有效性.