基于平节理模型的花岗岩固有微裂纹对裂纹演化影响分析

Influence of granite inherent microcracks on crack evolution based on the flat-joint contact model

模拟脆性岩石破坏时,现有的平节理模型没有考虑固有微裂纹导致的应力-应变曲线非线性特征,也没有将起裂强度作为细观参数的标定基准。以花岗岩单轴抗压强度、弹性模量、泊松比、应力-应变曲线特征、起裂强度、巴西劈裂抗拉强度、库仑摩擦角以及黏聚力作为基准,标定平节理模型细观参数,并分析宏细观参数间的趋势关系。以标定后的参数建立精确平节理模型试样,与不考虑固有微裂纹的常规平节理模型试样一起进行30°单裂纹岩石压缩数值试验,以室内试验数字图像相关方法得到的应变场为基础,对拉剪微裂纹萌生规律、数量以及分布特征进行分析,验证了提出的平节理模型参数标定方法,并表明固有微裂纹在宏观层面上改变了单轴压缩应力-应变曲线特征,而在细观层面上对预制裂隙尖端初始裂纹的起裂模式、拉剪微裂纹的扩展分布规律均有较大影响。

When simulating the failure of brittle rock,existing studies based on the flat joint model neither consider the nonlinear characteristics of stress-strain curve caused by inherent microcracks,nor take the crack initiation stress,an important indicator of damage evaluation,as the calibration benchmark for micro parameters.Therefore,this study used uniaxial compressive strength,elastic modulus,Poisson’s ratio,stress-strain curve characteristics,crack initiation stress,Brazilian splitting tensile strength,Coulomb friction angle and cohesive force as the benchmark to calibrate the micro parameters of the flat joint model for simulating granite failure.The trend relationships between the macro mechanical behaviors and micro parameters were analyzed.The calibrated parameters were used to establish an accurate flat joint model sample,which was compared with a conventional flat joint model sample that does not consider inherent microcracks.Numerical tests of fractured rock compression were carried out.Based on the strain field obtained by the digital image correlation method of the indoor test,the initiation,quantity and distribution characteristics of tensile/shear microcracks were analyzed to verify the calibration process of the flat joint model proposed in this paper.The results show that inherent microcracks influence the characteristics of the stress-strain curve at the macro level,and have a great impact on the crack initiation mode at the tip of the prefabricated flaw and the propagation and distribution law of tensile-shear microcracks at the meso level.