Rock brittleness is an essential mechanical property, which plays a significant role in rock classifications and rockburst risk evaluations. To overcome the problems associated with the traditional brittleness indexes not comprehensively charaterizing the rock strength and deformation behaviors, this study systematically summarized the existing rock brittleness indexes. Then, a novel brittleness index (BICSS) based on the complete stress–strain curves of rock under different confining pressures was proposed. Its advantages included innovatively considering the characteristic stresses and strains at the stage of crack initiation, the peak points, and residual points. The index also described the stress growth rates from the pre-peak crack-initiation stress to the peak stress points, as well as the stress drop rates from the peak stress to the residual stress points. This study conducted uniaxial and triaxial compression tests of metamorphic sandstone, granite, and gneiss obtained from a deeply buried long-line tunnel group. The aforementioned tests were combined with wave velocity tests and thin-section identification tests using polarizing microscopy techniques. The reliability and applicability of the index were then successfully verified. The results showed that the BICSS could not only quantify and classify the brittleness characteristics of different rock types and characterize the confining pressure inhibition behaviors of rock brittleness, but could also comprehensively express the influences of homogeneity, mineral compositions, and particle sizes on the rock brittleness. Finally, through the parameter sensitivity analysis of the BICSS, the influences of subjective errors in the results of the cracking initiation stress and strain values caused by the different selections during the linear elastic phase could be successfully excluded, resulting in the further verification of the stability of the BICSS.

中文翻译：

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基于完全应力应变特性的岩石脆性指数新指标

岩石脆性是一种重要的力学性质，在岩石分类和岩爆风险评估中起着重要作用。为了克服传统脆性指标不能全面表征岩石强度和变形行为的问题，本研究系统地总结了现有的岩石脆性指标。然后，基于岩石在不同围压下的完整应力-应变曲线，提出了一种新的脆性指数（BICSS）。其优点包括创新地考虑了裂纹萌生阶段、峰值点和残余点的特征应力和应变。该指数还描述了从预峰值裂纹起始应力到峰值应力点的应力增长速率，以及从峰值应力到残余应力点的应力下降率。本研究对从深埋延绳隧道群获得的变质砂岩、花岗岩和片麻岩进行了单轴和三轴压缩试验。上述测试与使用偏光显微镜技术的波速测试和薄片识别测试相结合。随后成功验证了该指标的可靠性和适用性。结果表明，BICSS不仅可以对不同岩石类型的脆性特征进行量化和分类，表征岩石脆性的围压抑制行为，还可以综合表达均质性、矿物成分、粒度对岩石脆性的影响。 . 最后，