The borehole method is quite commonly utilized in underground excavation engineering, such as for mining and tunneling, to release high pressure in brittle rock materials for safety control. In this paper, with the purpose of better understanding the failure behavior of brittle rock material with en echelon boreholes, a series of uniaxial compression tests were carried out on sandstone samples in the laboratory. The geometric layout of boreholes was the focus in this study and varied in terms of the number of borehole rows and orientation. In accordance with the experimental results, three failure modes were observed to occur in the sandstone samples, which are tensile failure across the borehole row, tensile failure along the borehole row, and a mixed failure mode. The strength and deformability of sandstone samples are found to significantly depend on the layout of boreholes. The variation in the brittleness of the rock materials was also analyzed with respect to the ratio of the initial stress over peak stress. The findings of this study would enhance the understanding of the borehole method and provide guidance for underground excavation engineering.

中文翻译：

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梯级孔脆性岩石材料力学行为的实验研究

钻孔法在地下挖掘工程中非常普遍，例如用于采矿和隧道，可释放脆性岩石材料中的高压以进行安全控制。为了更好地理解带有阶梯孔的脆性岩石材料的破坏行为，在实验室中对砂岩样品进行了一系列的单轴压缩试验。钻孔的几何布局是这项研究的重点，并且在钻孔排数和方向方面各不相同。根据实验结果，在砂岩样品中观察到了三种破坏模式，分别是整个井眼排的拉伸破坏，沿井眼排的拉伸破坏和混合破坏模式。发现砂岩样品的强度和可变形性在很大程度上取决于钻孔的布局。还针对初始应力与峰值应力之比分析了岩石材料的脆性变化。这项研究的结果将加深对钻孔方法的理解，并为地下挖掘工程提供指导。