This article presents a study on durability index obtained in the slake durability test (SDT) and the uniaxial compressive strength (UCS) of a gneissic rock from the Nova Venécia Complex, southeastern Brazil. The gneissic rock mass, excavated for a railway tunnel without a lining, has presented problems of instability of blocks due to a long-term exposure to weathering. The characterization of the gneissic rock matrix was made tactile and visual and by means of microscopical petrography, combining the tests of physical properties, SDT, and UCS with weathering indexes. The importance of describing the heterogeneity of the gneissic rock to interpret its influence on geotechnical parameters is discussed deeply. The interpretation of the results indicates that the rock studied has one facies with greater susceptibility to weathering, loss of strength, and durability. This study also proposes an equation to access the alterability parameter, recently added in the 2014 update of the rock mass rating (RMR), which may be overvalued to crystalline rocks, as observed in the analysis.

中文翻译：

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不同风化等级的片麻岩岩石耐久性指标与单轴抗压强度的关系

本文介绍了巴西东南部Nova Nova复杂的片麻岩岩石的耐久试验（SDT）和单轴抗压强度（UCS）获得的耐久性指数。在没有衬砌的铁路隧道中开挖的片麻岩岩体由于长期暴露在风化中而出现了砌块不稳定的问题。片麻质岩基质的表征是触觉和视觉的，并且借助显微岩石学，将物理性能，SDT和UCS的测试与风化指数相结合。深入讨论了描述片麻岩岩石非均质性以解释其对岩土参数的影响的重要性。结果的解释表明，所研究的岩石具有一种相，对风化的敏感性更大，强度降低，和耐用性。这项研究还提出了一个方程，用于访问可变性参数，该参数最近在2014年更新的岩体质量等级（RMR）中添加，如分析中所述，该数值可能被高估了结晶岩。