基于矿物晶体模型的非均质性岩石双裂纹扩展规律研究

Study on crack propagation of heterogeneous rocks with double flaws based on grain based model

为研究细观结构非均质性对裂隙岩石宏观力学及裂纹扩展规律的影响,基于花岗岩室内力学试验及矿物组成分析利用PFC离散元数值软件建立针对2种不同类型花岗岩的矿物晶体模型(grainbasedmodel,GBM),结合单裂纹岩石单轴压缩室内试验与数值模拟结果验证GBM的合理性与可靠性。对双裂隙岩石试样进行单轴和双轴压缩数值试验,分析研究应力-应变曲线、试样破坏模式及微裂纹的发展与演化规律。结果表明:岩石试样加载过程中的新生裂纹以晶内和晶间的拉伸裂纹为主,裂纹的发展可分为初始阶段、稳定发展阶段、快速发展阶段和峰后阶段;在10MPa条件下的双轴压缩中裂纹扩展的形态与单轴压缩相比具有中心对称和边缘延展2个明显的特性;峰值应力下各类型破坏裂纹数量随双轴试验围压增加呈现不同程度的增长趋势。从应变-裂纹数量角度分析,除晶间剪切裂纹外,围压对其他类型裂纹的前期发展存在不同程度的抑制作用;非均质性系数大的双裂隙岩石加载过程中更易出现应力集中且双轴压缩时破坏形式更易从拉伸破坏向剪切破坏转换。

To study the influence of meso-structural heterogeneity on macroscopic mechanical properties and crack propagation behaviors of fractured rocks,based on laboratory test and mineral composition analysis,the grain based models(GBM) of two types of granites were established using a discrete element numerical code PFC. The reliability and precision of the established GBM were verified against unconfined compression testing results of single flaw rock samples. Unconfined and biaxial compression numerical tests were carried out on double-flaw rock samples,and the stress-strain curve,the failure mode,and the development and evolution of microcracks were analyzed. The results show that intra-grain and inter-grain tensile cracks are primarily cracks and that the development of the cracks can be divided into initial stage,stably developing stage,rapidly developing stage and post peak stage during an entirely loading process. Compared with the unconfined compression,the morphology of crack growth under 10 MPa biaxial compression has two obvious characteristics such as center symmetry and edge extension. At the peak stress,the number of various types of cracks increases with increasing the confining pressure. In contrast,from the perspective of strain-crack number, the confining pressure has different degrees of inhibition effects on the early development of cracks except for inter-grain shear cracks. A rock with a greater heterogeneity coefficient is more prone to stress concentration in the loading process,and the failure mode can more easily transform from tensile failure to shear failure under biaxial compressions.