脆性岩石起裂应力水平与脆性指标关系探讨

 脆性指标与起裂应力作为岩石力学性质的内在体现，均反映岩石的非均质性和结构上的差异，二者存在一种必然的联系，通过理论研究和算例分析来探讨起裂应力水平与基于单轴抗压、抗拉强度比值的脆性指标的关系。首先，归纳总结基于压拉比、全应力–应变特征及硬度或坚固性的28种基本脆性测试方法。然后，研究硬脆性岩石单轴压缩起裂机制，讨论基于裂纹体积应变拐点的起裂应力确定方法，并定义起裂应力水平指标K。最后，结合具体工程算例探讨岩石起裂应力与基于压拉比的脆性指标的函数关系，深入验证起裂应力水平和脆性指标间内在联系的必然性。得出以下结论：(1) 以岩石单轴抗压、抗拉强度为纽带，建立起裂应力水平和脆性指标间的函数关系，根据单轴压缩起裂应力与单轴抗拉强度的关系，进一步验证脆性指标与起裂应力水平存在内在联系的必然性。(2) 岩石起裂应力水平与脆性指标B5和B6存在明显的函数关系，起裂应力水平与B5呈幂函数关系，与B6呈线性函数关系，相关系数均大于85%。(3) 采用起裂应力水平指标重新定义脆性指标，通过岩石的室内单轴压缩试验，由起裂应力水平可以快速得到岩石的脆性指标。通过这一研究，丰富了岩石起裂应力与脆性指标的关系，为脆性指标的计算提供了一条新思路。

RESEARCH ON RELATIONSHIP BETWEEN CRACK INITIATION STRESS LEVEL AND BRITTLENESS INDICES FOR BRITTLE ROCKS

Brittleness index and crack initiation stress，as the intrinsic reflection of mechanical properties for rock，reflect the heterogeneity and structural differences of rocks. Supposing that there exists a certain inevitable relationship between them，theoretical research and case study are conducted. Firstly，28 kinds of basic brittleness testing methods，based on ratio of uniaxial compressive strength to tensile strength，the whole stress-strain characteristics and hardness or soundness，are summarized. Secondly，the crack initiation mechanism for brittle rocks under uniaxial compression is studied. The method to determine crack initiation stress level is discussed by means of inflection points of crack volume strain curve；and the crack initiation stress level is defined as K. Finally，two cases are given to expose the function relationship between crack initiation stress and brittleness indices. Some conclusions are drawn as follows：(1) Based on the achievement of predecessors，by using the uniaxial compressive and tensile strengths，it is found that there exists a certain relation between crack initiation stress level and brittleness indices. (2) There are obvious function relationship between crack initiation stress level and brittleness indices B5，B6. To B5 is power function relation，and to B6 is linear function relation. The correlation coefficients are both greater than 85%，showing a strong correlation. (3) Brittleness index is redefined by crack initiation stress level，which can be obtained easily and quickly based on crack initiation stress level under uniaxial compression test. This study enriches the relationship between crack initiation stress and brittleness indices，and provides a new idea to determine the brittleness indices.