均质度对脆岩压缩破坏及裂纹扩展的影响规律

Influences of Failure Features and Fracture Development onHomogeneity Coefficient of Brittle Rock

为研究均质度对脆性岩石单轴压缩力学特性、破裂特征及裂纹扩展的影响规律,应用离散元UDEC软件建立了Voronoi块体集数值试件,借助FISH语言及Weibull分布函数实现了块体弹性模量及块体接触面抗拉强度的非均匀分布,开展了不同均质度系数下脆性花岗岩的单轴压缩模拟试验.结果表明:试件的抗压强度、弹性模量均随均质度系数增大而增大,而破坏前变形量则随均质度系数增大而减小,并都趋于稳定;试件宏观破裂形态呈X形共轭斜面剪破坏,细观破坏类型包括晶粒间及晶粒内部的拉、剪破坏;应力峰值前试件以拉破坏裂纹扩展为主,峰值后以剪破坏裂纹扩展为主;均质度系数越小,裂纹扩展及分布越分散,裂纹累计长度也越小,但在轴向应变小于0.2%时,拉破坏裂纹长度与均质度系数变化成反比,说明非均质程度较高的试件在压缩初期已开始出现拉破坏裂纹的扩展;此外,均质度系数为6.0的试件与均质试件的力学特性及裂纹扩展已较为接近,故在采用Weibull分布来描述岩石的非均质性时,均质度系数的取值不应过大.

To study the influence of the heterogeneity degree on the mechanical behavior,failure mode and fracture development of brittle rock under uniaxial compression,the universal discrete element software was used to construct some numerical specimens with an assemblage of Voronoi blocks.FISH language and the Weibull distribution function were combined to achieve the heterogeneous distribution of block elastic modulus and tensile strength on block contacts.Some uniaxial compression simulation tests of the brittle granite with various homogeneity coefficients were implemented.The results show that the compressive strength and elastic modulus of the specimens both increase with the increasing homogeneity coefficient,while the deformation before failure decreases with the increasing homogeneity coefficient,but the three indices all tend to stable.The specimens show X shape conjugate shear failure in macroscopic level,and the mesoscopic failure mainly consists of tensile and shear fractures between and in the crystalline grains.Tensile fracture propagation takes the dominant position before the peak stress and after that the shear fracture dominates the fracture development.For the specimens with smaller homogeneity coefficients,the fracture distribution and propagation were more dispersive and the cumulative length of the fractures is smaller,too.But the tensile fracture length shows a negative correlation with the changing homogeneity coefficients when the axial strain is less than 0.2%.This phenomenon indicates that tensile fractures start to initiate and propagate in early compression stage of specimens with high heterogeneity degrees.In addition,the mechanical behavior and fracture development law between the specimen with homogeneity coefficient of 6.0 and the homogeneous specimen are very close,so the value of homogeneity coefficient should not be too large when simulating heterogeneous rocks using Weibull distribution.