考虑应力变化速率的岩石脆性评价指标

Evaluation index of rock brittleness considering stress change rate

脆性作为岩石的重要的力学指标,对深部岩体性态评价以及灾害预防具有重要意义。岩石应力-应变曲线能够很好地表征岩石的脆性。考虑到现有基于应力-应变曲线的脆性指标大多都只对曲线的一部分进行分析,且少有指标能够准确地应用于岩石Ⅱ类曲线中,对整体判断的缺乏可能会导致工程应用上适应性及可靠性不足的情况。针对现有脆性指标普遍存在的物理意义模糊、评估结果与岩石脆性的关系非连续等问题,综合考量岩石应力-应变曲线中峰前应力上升速率、峰后应力跌落速率以及峰值点应变值对岩石脆性的影响,提出了一种物理意义明确、计算结果与岩石脆性之间的关系是单调且连续的岩石脆性指数计算方法。选取国内外常用脆性指标对锦屏Ⅱ级水电站大理岩和某铁路隧道花岗岩、变质砂岩以及片麻岩的单轴压缩试验数据进行脆性评价后进行比较,验证了指标的适用性。进一步将提出的指标应用于常规三轴试验条件下大理岩脆性分析,结果表明,该指标不仅能够量化和分类不同岩石的脆性特征,还能表征围压对岩石脆性的抑制作用。

As an important mechanical index of rocks,brittleness is of great significance for deep rock mass behavior assessment and disaster prevention.The stress-strain curve of rock can well represent rock brittleness.Considering that most of the existing brittleness indicators based on stress-strain curves only analyze a part of the curve,and few indices can be accurately applied to the rockⅡtype curve,lack of overall consideration may lead to the inadequate adaptability and reliability in engineering application.In order to solve those problems,such as the unclear physical meaning and the discontinuous relationship between the evaluation results and rock brittleness of the existing brittleness indices based on the complete stress-strain curve of rock,the influences of pre-peak stress rising rate,post-peak stress falling rate and peak strain on rock brittleness were analyzed,and a method of rock brittleness index with clear physical meaning,monotonous and continuous relationship between calculation results and rock brittleness was proposed.The commonly used brittleness indices were selected to compare the brittleness evaluation of the marble of JinpingⅡhydropower station and the granite,metamorphic sandstone and gneiss of a railway under uniaxial compression conditions,which verified the applicability of the index proposed.This novel brittleness index was further applied to the brittleness evaluation of marble under conventional triaxial test conditions.The results showed that this index could not only quantify and classify the brittleness characteristics of different rock types,but also characterize the confining pressure inhibition behaviors of rock brittleness.