预制裂纹几何与材料属性对岩石裂纹扩展的影响研究

RESEARCH ON INFLUENCE OF PRE-EXISTING CRACK GEOMETRICAL AND MATERIAL PROPERTIES ON CRACK PROPAGATION IN ROCKS

采用岩石破裂过程的弹塑性细胞自动机模拟系统EPCA2D,研究含预制裂纹岩石试件裂隙的几何位置以及基质材料力学属性的差异对裂纹扩展和搭接的影响。模拟中采用弱化元胞单元来表征试件中存在的预制裂纹,用Weibull随机分布对岩石基质元胞单元的力学参数进行赋值,以反映作为岩石基质一部分的岩桥的非均质性。表征预制裂纹的弱化元胞单元服从理想弹塑性本构关系,基质元胞单元服从弹脆塑性本构关系。利用该方法对含有2或3条裂纹的岩石试件进行单轴压缩破裂过程模拟,再现裂纹起裂、扩展和搭接全过程的实验现象。结果表明,预制裂纹的倾角和岩桥倾角对裂纹的扩展和搭接有重要的影响。同时,考虑基质材料力学属性的差异,研究基质元胞单元力学性质的随机空间分布和不同的内摩擦角等情况下的裂纹扩展模式,结果表明,裂纹的扩展和搭接路径强烈依赖于材料的力学属性,从机制上解释了室内实验中裂纹扩展路径离散性的原因。

The influences of pre-existing crack geometrical position and matrix material mechanical properties on crack propagation and coalescence are studied using self-developed numerical tool EPCA^2D. The weak cell element is used to represent the pre-existing cracks in rock specimens. The mechanical parameters of the cell element of rock matrix are assigned values by using Weibull＇s distribution to reflect the heterogeneity of rock bridge as a part of rock matrix. The pre-existing crack and the rock matrix conform to the perfect elastoplastic and elasto-brittle-plastic constitutive relation respectively. Using this method, the failure processes of rocks with two or three pre-existing cracks are simulated; and the phenomena of crack initiation, propagation and coalescence are well reproduced. It is concluded that the geometry of pre-existing cracks has great influence on the crack propagation and coalescence. At the same time, by considering different rock matrix properties, the failure patterns of rocks with different spatial random distributions of mechanical properties and different frictional angles etc. are numerically investigated. It is found that the crack propagation and coalescence paths are strongly dependent on the mechanical properties of materials, which can explain the reason why there exists diverse crack propagation paths in experiment.