Deep rock masses are in true triaxial stress (TTS) fields, and few studies have examined the brittleness evaluation of rock under TTS thus far. In particular, research has not been conducted on the brittleness evaluation index and the effect of TTS. Therefore, based on a summary and analysis of pre-existing brittleness indexes, this paper proposes a brittleness index of rock under TTS that considers both stress-induced anisotropy and energy conversion characteristics during Class I behavior and Class II behavior. Meanwhile, the studied brittleness index is analyzed and verified. The brittleness of rock was found to increase with increasing σ2 while σ3 is constant; when σ2 is constant, the rock brittleness decreases with the increase in σ3. When σ3 is high, the increase in the rock brittleness amplitude with increasing σ2 is large; conversely, when σ3 is low, the amplitude is small. For the same σ3 (σ3 = 5 MPa), the order of brittleness of the three rocks is basalt > granite > marble. Finally, this paper shows that the proposed brittleness index can be applied to conventional triaxial and uniaxial stresses. In addition, under different TTS, a brittleness threshold of σ2/σ3 = 5 was found for the rocks, and when σ2/σ3 < 5, the rock brittleness enters a stress sensitive zone. The research results in this study can provide a relevant basis and guidance for the study of the brittle fracture process and the brittleness of rock under TTS.

中文翻译：

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基于峰前变形特征和峰后能量演化的真三轴应力状态下岩石脆性评价方法

深部岩体处于真三轴应力（TTS）场，迄今为止很少有研究对TTS下岩石的脆性评价进行研究。尤其是脆性评价指标和TTS的效果尚未进行研究。因此，本文在对已有脆性指标进行总结和分析的基础上，提出了一种兼顾应力诱导各向异性和能量转换特性的TTS下岩石脆性指标，即I类行为和II类行为。同时，对研究的脆性指标进行了分析和验证。发现岩石的脆性随着σ2的增加而增加，而σ3不变；当σ2 不变时，岩石脆性随着σ3 的增加而降低。σ3 大时，岩石脆性幅度随σ2 增大而增大；反过来，当 σ3 低时，幅度小。对于相同的σ3（σ3=5 MPa），三种岩石的脆性顺序为玄武岩>花岗岩>大理岩。最后，本文表明所提出的脆性指数可以应用于常规的三轴和单轴应力。此外，在不同的TTS下，岩石的脆性阈值为σ2/σ3=5，当σ2/σ3<5时，岩石脆性进入应力敏感区。本研究成果可为TTS作用下岩石脆性断裂过程及脆性研究提供相关依据和指导。本文表明，所提出的脆性指数可以应用于传统的三轴和单轴应力。此外，在不同的TTS下，岩石的脆性阈值为σ2/σ3=5，当σ2/σ3<5时，岩石脆性进入应力敏感区。本研究成果可为TTS作用下岩石脆性断裂过程及脆性研究提供相关依据和指导。本文表明，所提出的脆性指数可以应用于传统的三轴和单轴应力。此外，在不同的TTS下，岩石的脆性阈值为σ2/σ3=5，当σ2/σ3<5时，岩石脆性进入应力敏感区。本研究成果可为TTS作用下岩石脆性断裂过程及脆性研究提供相关依据和指导。