预压脆性岩石动态宏细观力学模型研究

预压应力脆性岩石动力特性研究,对深部地下工程围岩变形评价有重要实践意义。细观裂纹扩展严重影响预压脆性岩石动态力学行为。基于细观裂纹扩展与应力关系模型、裂纹速率与动态断裂韧度模型、裂纹速率与应变率关系模型及应变率与应变关系模型,提出了一种考虑预压轴向应力及围压的脆性岩石承受动态荷载作用下的宏细观力学模型。其中裂纹速率与应变率关系模型是通过对应变相关的裂纹长度求解时间导数获得。应变率与应变关系模型描述了预压岩石动态荷载导致的应变率随应变演化曲线。研究了不同预压轴向应力及应变率影响下的脆性岩石应力-应变关系曲线,并利用试验结果验证了模型的合理性。讨论了围压、初始裂纹尺寸、初始裂纹角度、及初始裂纹摩擦系数对预压应力岩石的动态应力应变关系、预压裂纹长度、预压轴向应变、及动态峰值强度的影响。主要研究结果:预压应力越小、围压越大、初始裂纹面尺寸越小或初始裂纹摩擦系数越大,则预压轴向应变及裂纹长度越小,且预压岩石动态强度越大。

Dynamic Macro-Micro Mechanical Model of Brittle Rocks under Precompression

Research of dynamic mechanical properties under precompression of brittle rocks have significant practical meaning for estimating surrounding rock deformation in deep underground engineering. The behaviour of crack growth strongly influences the dynamic mechanical properties under pre-compressive loadings in brittle rocks. Using the relation between crack extension and stress, the relation between crack velocity and fracture toughness, the relation between crack velocity and strain rate, and the relation between strain rate and strain, a micro-macro model is proposed to explain the dynamic mechanics under precompression of brittle rocks. The relation between crack velocity and strain rate is established by time derivation of suggested expression of the crack length correlating to the strain. The relation between strain rate and strain describes the variation of strain rate with strain under dynamic loadings and pre-compressive loadings. The effects of axial pre-compressive stress and strain rate on the dynamic stress-strain curves under precompression are studied. The rationality of the proposed model is validated by tests. The effects of confining pressure, initial crack size, initial crack angle, and initial crack friction coefficient on the dynamic stress-strain curve, pre-crack length, pre-axial strain, and peak strength under precompression are discussed in details. The main research results: the dynamic strength under precompression increases, and the pre-axial strain and pre-crack length decrease with the decrement of precompression stress and initial crack size, and with the increment of strain rate, confining pressure and initial crack friction coefficient.